diff --git a/example/imageviewer/imageviewer.cc b/example/imageviewer/imageviewer.cc
index 3e6e2c4..3b12f89 100644
--- a/example/imageviewer/imageviewer.cc
+++ b/example/imageviewer/imageviewer.cc
@@ -111,7 +111,7 @@
   wuffs_aux::DecodeImageCallbacks callbacks;
   wuffs_aux::sync_io::FileInput input(file);
   wuffs_aux::DecodeImageResult res = wuffs_aux::DecodeImage(
-      callbacks, input, WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL,
+      callbacks, input,
       // Use PIXEL_BLEND__SRC_OVER, not the default PIXEL_BLEND__SRC, because
       // we also pass a background color.
       WUFFS_BASE__PIXEL_BLEND__SRC_OVER,
diff --git a/internal/cgen/auxiliary/image.cc b/internal/cgen/auxiliary/image.cc
index fded2ef..d50cab4 100644
--- a/internal/cgen/auxiliary/image.cc
+++ b/internal/cgen/auxiliary/image.cc
@@ -49,7 +49,7 @@
       error_message(std::move(error_message0)) {}
 
 wuffs_base__image_decoder::unique_ptr  //
-DecodeImageCallbacks::OnImageFormat(uint32_t fourcc,
+DecodeImageCallbacks::SelectDecoder(uint32_t fourcc,
                                     wuffs_base__slice_u8 prefix) {
   switch (fourcc) {
 #if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__BMP)
@@ -85,10 +85,16 @@
   return wuffs_base__image_decoder::unique_ptr(nullptr, &free);
 }
 
+wuffs_base__pixel_format  //
+DecodeImageCallbacks::SelectPixfmt(
+    const wuffs_base__image_config& image_config) {
+  return wuffs_base__make_pixel_format(
+      WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL);
+}
+
 DecodeImageCallbacks::AllocResult  //
-DecodeImageCallbacks::OnImageConfig(
-    const wuffs_base__image_config& image_config,
-    bool allow_uninitialized_memory) {
+DecodeImageCallbacks::AllocPixbuf(const wuffs_base__image_config& image_config,
+                                  bool allow_uninitialized_memory) {
   uint32_t w = image_config.pixcfg.width();
   uint32_t h = image_config.pixcfg.height();
   if ((w == 0) || (h == 0)) {
@@ -186,21 +192,10 @@
              DecodeImageCallbacks& callbacks,
              sync_io::Input& input,
              wuffs_base__io_buffer& io_buf,
-             uint32_t override_pixel_format_repr,
              wuffs_base__pixel_blend pixel_blend,
              wuffs_base__color_u32_argb_premul background_color,
              uint32_t max_incl_dimension) {
   // Check args.
-  switch (override_pixel_format_repr) {
-    case 0:
-    case WUFFS_BASE__PIXEL_FORMAT__BGR_565:
-    case WUFFS_BASE__PIXEL_FORMAT__BGR:
-    case WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL:
-    case WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL:
-      break;
-    default:
-      return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);
-  }
   switch (pixel_blend) {
     case WUFFS_BASE__PIXEL_BLEND__SRC:
     case WUFFS_BASE__PIXEL_BLEND__SRC_OVER:
@@ -256,8 +251,8 @@
       image_decoder.reset();
     }
 
-    // Make the image decoder.
-    image_decoder = callbacks.OnImageFormat(
+    // Select the image decoder.
+    image_decoder = callbacks.SelectDecoder(
         (uint32_t)fourcc,
         fourcc ? wuffs_base__empty_slice_u8() : io_buf.reader_slice());
     if (!image_decoder) {
@@ -289,14 +284,24 @@
     }
   } while (false);
 
-  // Apply the override pixel format.
+  // Select the pixel format.
   uint32_t w = image_config.pixcfg.width();
   uint32_t h = image_config.pixcfg.height();
   if ((w > max_incl_dimension) || (h > max_incl_dimension)) {
     return DecodeImageResult(DecodeImage_MaxInclDimensionExceeded);
   }
-  if (override_pixel_format_repr != 0) {
-    image_config.pixcfg.set(override_pixel_format_repr,
+  wuffs_base__pixel_format pixel_format = callbacks.SelectPixfmt(image_config);
+  if (pixel_format.repr != image_config.pixcfg.pixel_format().repr) {
+    switch (pixel_format.repr) {
+      case WUFFS_BASE__PIXEL_FORMAT__BGR_565:
+      case WUFFS_BASE__PIXEL_FORMAT__BGR:
+      case WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL:
+      case WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL:
+        break;
+      default:
+        return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);
+    }
+    image_config.pixcfg.set(pixel_format.repr,
                             WUFFS_BASE__PIXEL_SUBSAMPLING__NONE, w, h);
   }
 
@@ -310,16 +315,16 @@
   }
   bool valid_background_color =
       wuffs_base__color_u32_argb_premul__is_valid(background_color);
-  DecodeImageCallbacks::AllocResult oic_result =
-      callbacks.OnImageConfig(image_config, valid_background_color);
-  if (!oic_result.error_message.empty()) {
-    return DecodeImageResult(std::move(oic_result.error_message));
-  } else if (oic_result.mem_slice.len < pixbuf_len_min_incl) {
+  DecodeImageCallbacks::AllocResult alloc_pixbuf_result =
+      callbacks.AllocPixbuf(image_config, valid_background_color);
+  if (!alloc_pixbuf_result.error_message.empty()) {
+    return DecodeImageResult(std::move(alloc_pixbuf_result.error_message));
+  } else if (alloc_pixbuf_result.mem_slice.len < pixbuf_len_min_incl) {
     return DecodeImageResult(DecodeImage_BufferIsTooShort);
   }
   wuffs_base__pixel_buffer pixel_buffer;
-  wuffs_base__status pb_sfs_status =
-      pixel_buffer.set_from_slice(&image_config.pixcfg, oic_result.mem_slice);
+  wuffs_base__status pb_sfs_status = pixel_buffer.set_from_slice(
+      &image_config.pixcfg, alloc_pixbuf_result.mem_slice);
   if (!pb_sfs_status.is_ok()) {
     return DecodeImageResult(pb_sfs_status.message());
   }
@@ -390,8 +395,8 @@
       }
     }
   }
-  return DecodeImageResult(std::move(oic_result.mem_owner),
-                           oic_result.mem_slice, pixel_buffer,
+  return DecodeImageResult(std::move(alloc_pixbuf_result.mem_owner),
+                           alloc_pixbuf_result.mem_slice, pixel_buffer,
                            std::move(message));
 }
 
@@ -400,7 +405,6 @@
 DecodeImageResult  //
 DecodeImage(DecodeImageCallbacks& callbacks,
             sync_io::Input& input,
-            uint32_t override_pixel_format_repr,
             wuffs_base__pixel_blend pixel_blend,
             wuffs_base__color_u32_argb_premul background_color,
             uint32_t max_incl_dimension) {
@@ -415,9 +419,9 @@
   }
 
   wuffs_base__image_decoder::unique_ptr image_decoder(nullptr, &free);
-  DecodeImageResult result = DecodeImage0(
-      image_decoder, callbacks, input, *io_buf, override_pixel_format_repr,
-      pixel_blend, background_color, max_incl_dimension);
+  DecodeImageResult result =
+      DecodeImage0(image_decoder, callbacks, input, *io_buf, pixel_blend,
+                   background_color, max_incl_dimension);
   callbacks.Done(result, input, *io_buf, std::move(image_decoder));
   return result;
 }
diff --git a/internal/cgen/auxiliary/image.hh b/internal/cgen/auxiliary/image.hh
index 458cf49..775cdc7 100644
--- a/internal/cgen/auxiliary/image.hh
+++ b/internal/cgen/auxiliary/image.hh
@@ -33,14 +33,14 @@
 
 // DecodeImageCallbacks are the callbacks given to DecodeImage. They are always
 // called in this order:
-//  1. OnImageFormat
-//  2. OnImageConfig
-//  3. AllocWorkbuf
-//  4. Done
+//  1. SelectDecoder
+//  2. SelectPixfmt
+//  3. AllocPixbuf
+//  4. AllocWorkbuf
+//  5. Done
 //
 // It may return early - the third callback might not be invoked if the second
-// one fails (returns a non-empty error message) - but the final callback
-// (Done) is always invoked.
+// one fails - but the final callback (Done) is always invoked.
 class DecodeImageCallbacks {
  public:
   // AllocResult holds a memory allocation (the result of malloc or new, a
@@ -55,19 +55,19 @@
     std::string error_message;
   };
 
-  // OnImageFormat returns the image decoder for the input data's file format.
+  // SelectDecoder returns the image decoder for the input data's file format.
   // Returning a nullptr means failure (DecodeImage_UnsupportedImageFormat).
   //
   // Common formats will have a FourCC value in the range [1 ..= 0x7FFF_FFFF],
   // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that the
   // caller is responsible for examining the opening bytes (a prefix) of the
-  // input data. OnImageFormat implementations should not modify those bytes.
+  // input data. SelectDecoder implementations should not modify those bytes.
   //
-  // OnImageFormat might be called more than once, since some image file
+  // SelectDecoder might be called more than once, since some image file
   // formats can wrap others. For example, a nominal BMP file can actually
   // contain a JPEG or a PNG.
   //
-  // The default OnImageFormat accepts the FOURCC codes listed below. For
+  // The default SelectDecoder accepts the FOURCC codes listed below. For
   // modular builds (i.e. when #define'ing WUFFS_CONFIG__MODULES), acceptance
   // of the ETC file format is optional (for each value of ETC) and depends on
   // the corresponding module to be enabled at compile time (i.e. #define'ing
@@ -78,20 +78,38 @@
   //  - WUFFS_BASE__FOURCC__PNG
   //  - WUFFS_BASE__FOURCC__WBMP
   virtual wuffs_base__image_decoder::unique_ptr  //
-  OnImageFormat(uint32_t fourcc, wuffs_base__slice_u8 prefix);
+  SelectDecoder(uint32_t fourcc, wuffs_base__slice_u8 prefix);
 
-  // OnImageConfig allocates the pixel buffer.
+  // SelectPixfmt returns the destination pixel format for AllocPixbuf. It
+  // should return wuffs_base__make_pixel_format(etc) called with one of:
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGR_565
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGR
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL
+  // or return image_config.pixcfg.pixel_format(). The latter means to use the
+  // image file's natural pixel format. For example, GIF images' natural pixel
+  // format is an indexed one.
+  //
+  // Returning otherwise means failure (DecodeImage_UnsupportedPixelFormat).
+  //
+  // The default SelectPixfmt implementation returns
+  // wuffs_base__make_pixel_format(WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL)
+  // which is 4 bytes per pixel (8 bits per channel × 4 channels).
+  virtual wuffs_base__pixel_format  //
+  SelectPixfmt(const wuffs_base__image_config& image_config);
+
+  // AllocPixbuf allocates the pixel buffer.
   //
   // allow_uninitialized_memory will be true if a valid background_color was
   // passed to DecodeImage, since the pixel buffer's contents will be
-  // overwritten with that color after OnImageConfig returns.
+  // overwritten with that color after AllocPixbuf returns.
   //
-  // The default OnImageConfig implementation allocates either uninitialized or
+  // The default AllocPixbuf implementation allocates either uninitialized or
   // zeroed memory. Zeroed memory typically corresponds to filling with opaque
   // black or transparent black, depending on the pixel format.
   virtual AllocResult  //
-  OnImageConfig(const wuffs_base__image_config& image_config,
-                bool allow_uninitialized_memory);
+  AllocPixbuf(const wuffs_base__image_config& image_config,
+              bool allow_uninitialized_memory);
 
   // AllocWorkbuf allocates the work buffer. The allocated buffer's length
   // should be at least len_range.min_incl, but larger allocations (up to
@@ -107,7 +125,7 @@
   // not parsing the input encountered an error. Even when successful, trailing
   // data may remain in input and buffer.
   //
-  // The image_decoder is the one returned by OnImageFormat (if OnImageFormat
+  // The image_decoder is the one returned by SelectDecoder (if SelectDecoder
   // was successful), or a no-op unique_ptr otherwise. Like any unique_ptr,
   // ownership moves to the Done implementation.
   //
@@ -133,7 +151,7 @@
 extern const char DecodeImage_UnsupportedPixelFormat[];
 
 // DecodeImage decodes the image data in input. A variety of image file formats
-// can be decoded, depending on what callbacks.OnImageFormat returns.
+// can be decoded, depending on what callbacks.SelectDecoder returns.
 //
 // For animated formats, only the first frame is returned, since the API is
 // simpler for synchronous I/O and having DecodeImage only return when
@@ -158,25 +176,14 @@
 // as the returned pixbuf_mem_owner. Regardless of success or failure, the work
 // buffer memory is deleted.
 //
-// If override_pixel_format_repr is zero then the pixel buffer will have the
-// image file's natural pixel format. For example, GIF images' natural pixel
-// format is an indexed one.
-//
-// If override_pixel_format_repr is non-zero (and one of the constants listed
-// below) then the image will be decoded to that particular pixel format:
-//  - WUFFS_BASE__PIXEL_FORMAT__BGR_565
-//  - WUFFS_BASE__PIXEL_FORMAT__BGR
-//  - WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL
-//  - WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL
-//
 // The pixel_blend (one of the constants listed below) determines how to
 // composite the decoded image over the pixel buffer's original pixels (as
-// returned by callbacks.OnImageConfig):
+// returned by callbacks.AllocPixbuf):
 //  - WUFFS_BASE__PIXEL_BLEND__SRC
 //  - WUFFS_BASE__PIXEL_BLEND__SRC_OVER
 //
 // The background_color is used to fill the pixel buffer after
-// callbacks.OnImageConfig returns, if it is valid in the
+// callbacks.AllocPixbuf returns, if it is valid in the
 // wuffs_base__color_u32_argb_premul__is_valid sense. The default value,
 // 0x0000_0001, is not valid since its Blue channel value (0x01) is greater
 // than its Alpha channel value (0x00). A valid background_color will typically
@@ -189,7 +196,6 @@
 DecodeImageResult  //
 DecodeImage(DecodeImageCallbacks& callbacks,
             sync_io::Input& input,
-            uint32_t override_pixel_format_repr,
             wuffs_base__pixel_blend pixel_blend = WUFFS_BASE__PIXEL_BLEND__SRC,
             wuffs_base__color_u32_argb_premul background_color = 1,  // Invalid.
             uint32_t max_incl_dimension = 1048575);  // 0x000F_FFFF
diff --git a/internal/cgen/data/data.go b/internal/cgen/data/data.go
index 3d4114f..d3df782 100644
--- a/internal/cgen/data/data.go
+++ b/internal/cgen/data/data.go
@@ -740,35 +740,35 @@
 
 const AuxImageCc = "" +
 	"// ---------------- Auxiliary - Image\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__AUX__IMAGE)\n\n#include <utility>\n\nnamespace wuffs_aux {\n\nDecodeImageResult::DecodeImageResult(MemOwner&& pixbuf_mem_owner0,\n                                     wuffs_base__slice_u8 pixbuf_mem_slice0,\n                                     wuffs_base__pixel_buffer pixbuf0,\n                                     std::string&& error_message0)\n    : pixbuf_mem_owner(std::move(pixbuf_mem_owner0)),\n      pixbuf_mem_slice(pixbuf_mem_slice0),\n      pixbuf(pixbuf0),\n      error_message(std::move(error_message0)) {}\n\nDecodeImageResult::DecodeImageResult(std::string&& error_message0)\n    : pixbuf_mem_owner(nullptr, &free),\n      pixbuf_mem_slice(wuffs_base__empty_slice_u8()),\n      pixbuf(wuffs_base__null_pixel_buffer()),\n      error_message(std::move(error_message0)) {}\n\nDecodeImageCallbacks::AllocResult::AllocResult(MemOwner&& mem_owner0,\n                                               wuffs_base__slice_u8 mem_slice0" +
-	")\n    : mem_owner(std::move(mem_owner0)),\n      mem_slice(mem_slice0),\n      error_message(\"\") {}\n\nDecodeImageCallbacks::AllocResult::AllocResult(std::string&& error_message0)\n    : mem_owner(nullptr, &free),\n      mem_slice(wuffs_base__empty_slice_u8()),\n      error_message(std::move(error_message0)) {}\n\nwuffs_base__image_decoder::unique_ptr  //\nDecodeImageCallbacks::OnImageFormat(uint32_t fourcc,\n                                    wuffs_base__slice_u8 prefix) {\n  switch (fourcc) {\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__BMP)\n    case WUFFS_BASE__FOURCC__BMP:\n      return wuffs_bmp__decoder::alloc_as__wuffs_base__image_decoder();\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__GIF)\n    case WUFFS_BASE__FOURCC__GIF:\n      return wuffs_gif__decoder::alloc_as__wuffs_base__image_decoder();\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__NIE)\n    case WUFFS_BASE__FOURCC__NIE:\n      return wuffs_nie__decoder::alloc_as__wuffs_ba" +
-	"se__image_decoder();\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__PNG)\n    case WUFFS_BASE__FOURCC__PNG: {\n      auto dec = wuffs_png__decoder::alloc_as__wuffs_base__image_decoder();\n      // Favor faster decodes over rejecting invalid checksums.\n      dec->set_quirk_enabled(WUFFS_BASE__QUIRK_IGNORE_CHECKSUM, true);\n      return dec;\n    }\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__WBMP)\n    case WUFFS_BASE__FOURCC__WBMP:\n      return wuffs_wbmp__decoder::alloc_as__wuffs_base__image_decoder();\n#endif\n  }\n\n  return wuffs_base__image_decoder::unique_ptr(nullptr, &free);\n}\n\nDecodeImageCallbacks::AllocResult  //\nDecodeImageCallbacks::OnImageConfig(\n    const wuffs_base__image_config& image_config,\n    bool allow_uninitialized_memory) {\n  uint32_t w = image_config.pixcfg.width();\n  uint32_t h = image_config.pixcfg.height();\n  if ((w == 0) || (h == 0)) {\n    return AllocResult(\"\");\n  }\n  uint64_t len = image_config.pixcfg.pixbuf_len();\n  if ((len == " +
-	"0) || (SIZE_MAX < len)) {\n    return AllocResult(DecodeImage_UnsupportedPixelConfiguration);\n  }\n  void* ptr =\n      allow_uninitialized_memory ? malloc((size_t)len) : calloc((size_t)len, 1);\n  return ptr ? AllocResult(\n                   MemOwner(ptr, &free),\n                   wuffs_base__make_slice_u8((uint8_t*)ptr, (size_t)len))\n             : AllocResult(DecodeImage_OutOfMemory);\n}\n\nDecodeImageCallbacks::AllocResult  //\nDecodeImageCallbacks::AllocWorkbuf(wuffs_base__range_ii_u64 len_range,\n                                   bool allow_uninitialized_memory) {\n  uint64_t len = len_range.max_incl;\n  if (len == 0) {\n    return AllocResult(\"\");\n  } else if (SIZE_MAX < len) {\n    return AllocResult(DecodeImage_OutOfMemory);\n  }\n  void* ptr =\n      allow_uninitialized_memory ? malloc((size_t)len) : calloc((size_t)len, 1);\n  return ptr ? AllocResult(\n                   MemOwner(ptr, &free),\n                   wuffs_base__make_slice_u8((uint8_t*)ptr, (size_t)len))\n             : AllocResult(DecodeImage_OutOfMemor" +
-	"y);\n}\n\nvoid  //\nDecodeImageCallbacks::Done(\n    DecodeImageResult& result,\n    sync_io::Input& input,\n    IOBuffer& buffer,\n    wuffs_base__image_decoder::unique_ptr image_decoder) {}\n\nconst char DecodeImage_BufferIsTooShort[] =  //\n    \"wuffs_aux::DecodeImage: buffer is too short\";\nconst char DecodeImage_MaxInclDimensionExceeded[] =  //\n    \"wuffs_aux::DecodeImage: max_incl_dimension exceeded\";\nconst char DecodeImage_OutOfMemory[] =  //\n    \"wuffs_aux::DecodeImage: out of memory\";\nconst char DecodeImage_UnexpectedEndOfFile[] =  //\n    \"wuffs_aux::DecodeImage: unexpected end of file\";\nconst char DecodeImage_UnsupportedImageFormat[] =  //\n    \"wuffs_aux::DecodeImage: unsupported image format\";\nconst char DecodeImage_UnsupportedPixelBlend[] =  //\n    \"wuffs_aux::DecodeImage: unsupported pixel blend\";\nconst char DecodeImage_UnsupportedPixelConfiguration[] =  //\n    \"wuffs_aux::DecodeImage: unsupported pixel configuration\";\nconst char DecodeImage_UnsupportedPixelFormat[] =  //\n    \"wuffs_aux::DecodeImage: unsuppo" +
-	"rted pixel format\";\n\n" +
+	")\n    : mem_owner(std::move(mem_owner0)),\n      mem_slice(mem_slice0),\n      error_message(\"\") {}\n\nDecodeImageCallbacks::AllocResult::AllocResult(std::string&& error_message0)\n    : mem_owner(nullptr, &free),\n      mem_slice(wuffs_base__empty_slice_u8()),\n      error_message(std::move(error_message0)) {}\n\nwuffs_base__image_decoder::unique_ptr  //\nDecodeImageCallbacks::SelectDecoder(uint32_t fourcc,\n                                    wuffs_base__slice_u8 prefix) {\n  switch (fourcc) {\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__BMP)\n    case WUFFS_BASE__FOURCC__BMP:\n      return wuffs_bmp__decoder::alloc_as__wuffs_base__image_decoder();\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__GIF)\n    case WUFFS_BASE__FOURCC__GIF:\n      return wuffs_gif__decoder::alloc_as__wuffs_base__image_decoder();\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__NIE)\n    case WUFFS_BASE__FOURCC__NIE:\n      return wuffs_nie__decoder::alloc_as__wuffs_ba" +
+	"se__image_decoder();\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__PNG)\n    case WUFFS_BASE__FOURCC__PNG: {\n      auto dec = wuffs_png__decoder::alloc_as__wuffs_base__image_decoder();\n      // Favor faster decodes over rejecting invalid checksums.\n      dec->set_quirk_enabled(WUFFS_BASE__QUIRK_IGNORE_CHECKSUM, true);\n      return dec;\n    }\n#endif\n\n#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__WBMP)\n    case WUFFS_BASE__FOURCC__WBMP:\n      return wuffs_wbmp__decoder::alloc_as__wuffs_base__image_decoder();\n#endif\n  }\n\n  return wuffs_base__image_decoder::unique_ptr(nullptr, &free);\n}\n\nwuffs_base__pixel_format  //\nDecodeImageCallbacks::SelectPixfmt(\n    const wuffs_base__image_config& image_config) {\n  return wuffs_base__make_pixel_format(\n      WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL);\n}\n\nDecodeImageCallbacks::AllocResult  //\nDecodeImageCallbacks::AllocPixbuf(const wuffs_base__image_config& image_config,\n                                  bool allow_uninitia" +
+	"lized_memory) {\n  uint32_t w = image_config.pixcfg.width();\n  uint32_t h = image_config.pixcfg.height();\n  if ((w == 0) || (h == 0)) {\n    return AllocResult(\"\");\n  }\n  uint64_t len = image_config.pixcfg.pixbuf_len();\n  if ((len == 0) || (SIZE_MAX < len)) {\n    return AllocResult(DecodeImage_UnsupportedPixelConfiguration);\n  }\n  void* ptr =\n      allow_uninitialized_memory ? malloc((size_t)len) : calloc((size_t)len, 1);\n  return ptr ? AllocResult(\n                   MemOwner(ptr, &free),\n                   wuffs_base__make_slice_u8((uint8_t*)ptr, (size_t)len))\n             : AllocResult(DecodeImage_OutOfMemory);\n}\n\nDecodeImageCallbacks::AllocResult  //\nDecodeImageCallbacks::AllocWorkbuf(wuffs_base__range_ii_u64 len_range,\n                                   bool allow_uninitialized_memory) {\n  uint64_t len = len_range.max_incl;\n  if (len == 0) {\n    return AllocResult(\"\");\n  } else if (SIZE_MAX < len) {\n    return AllocResult(DecodeImage_OutOfMemory);\n  }\n  void* ptr =\n      allow_uninitialized_memory ? malloc" +
+	"((size_t)len) : calloc((size_t)len, 1);\n  return ptr ? AllocResult(\n                   MemOwner(ptr, &free),\n                   wuffs_base__make_slice_u8((uint8_t*)ptr, (size_t)len))\n             : AllocResult(DecodeImage_OutOfMemory);\n}\n\nvoid  //\nDecodeImageCallbacks::Done(\n    DecodeImageResult& result,\n    sync_io::Input& input,\n    IOBuffer& buffer,\n    wuffs_base__image_decoder::unique_ptr image_decoder) {}\n\nconst char DecodeImage_BufferIsTooShort[] =  //\n    \"wuffs_aux::DecodeImage: buffer is too short\";\nconst char DecodeImage_MaxInclDimensionExceeded[] =  //\n    \"wuffs_aux::DecodeImage: max_incl_dimension exceeded\";\nconst char DecodeImage_OutOfMemory[] =  //\n    \"wuffs_aux::DecodeImage: out of memory\";\nconst char DecodeImage_UnexpectedEndOfFile[] =  //\n    \"wuffs_aux::DecodeImage: unexpected end of file\";\nconst char DecodeImage_UnsupportedImageFormat[] =  //\n    \"wuffs_aux::DecodeImage: unsupported image format\";\nconst char DecodeImage_UnsupportedPixelBlend[] =  //\n    \"wuffs_aux::DecodeImage: unsuppor" +
+	"ted pixel blend\";\nconst char DecodeImage_UnsupportedPixelConfiguration[] =  //\n    \"wuffs_aux::DecodeImage: unsupported pixel configuration\";\nconst char DecodeImage_UnsupportedPixelFormat[] =  //\n    \"wuffs_aux::DecodeImage: unsupported pixel format\";\n\n" +
 	"" +
 	"// --------\n\nnamespace {\n\nstd::string  //\nDecodeImageAdvanceIOBuf(sync_io::Input& input,\n                        wuffs_base__io_buffer& io_buf,\n                        bool compactable,\n                        uint64_t min_excl_pos,\n                        uint64_t pos) {\n  if ((pos <= min_excl_pos) || (pos < io_buf.reader_position())) {\n    // Redirects must go forward.\n    return DecodeImage_UnsupportedImageFormat;\n  }\n  while (true) {\n    uint64_t relative_pos = pos - io_buf.reader_position();\n    if (relative_pos <= io_buf.reader_length()) {\n      io_buf.meta.ri += (size_t)relative_pos;\n      break;\n    } else if (io_buf.meta.closed) {\n      return DecodeImage_UnexpectedEndOfFile;\n    }\n    io_buf.meta.ri = io_buf.meta.wi;\n    if (compactable) {\n      io_buf.compact();\n    }\n    std::string error_message = input.CopyIn(&io_buf);\n    if (!error_message.empty()) {\n      return error_message;\n    }\n  }\n  return \"\";\n}\n\nDecodeImageResult  //\nDecodeImage0(wuffs_base__image_decoder::unique_ptr& image_decoder,\n  " +
-	"           DecodeImageCallbacks& callbacks,\n             sync_io::Input& input,\n             wuffs_base__io_buffer& io_buf,\n             uint32_t override_pixel_format_repr,\n             wuffs_base__pixel_blend pixel_blend,\n             wuffs_base__color_u32_argb_premul background_color,\n             uint32_t max_incl_dimension) {\n  // Check args.\n  switch (override_pixel_format_repr) {\n    case 0:\n    case WUFFS_BASE__PIXEL_FORMAT__BGR_565:\n    case WUFFS_BASE__PIXEL_FORMAT__BGR:\n    case WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL:\n    case WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL:\n      break;\n    default:\n      return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);\n  }\n  switch (pixel_blend) {\n    case WUFFS_BASE__PIXEL_BLEND__SRC:\n    case WUFFS_BASE__PIXEL_BLEND__SRC_OVER:\n      break;\n    default:\n      return DecodeImageResult(DecodeImage_UnsupportedPixelBlend);\n  }\n\n  wuffs_base__image_config image_config = wuffs_base__null_image_config();\n  uint64_t start_pos = io_buf.reader_position();\n  bool redi" +
-	"rected = false;\n  int32_t fourcc = 0;\nredirect:\n  do {\n    // Determine the image format.\n    if (!redirected) {\n      while (true) {\n        fourcc = wuffs_base__magic_number_guess_fourcc(io_buf.reader_slice());\n        if (fourcc > 0) {\n          break;\n        } else if ((fourcc == 0) && (io_buf.reader_length() >= 64)) {\n          break;\n        } else if (io_buf.meta.closed || (io_buf.writer_length() == 0)) {\n          fourcc = 0;\n          break;\n        }\n        std::string error_message = input.CopyIn(&io_buf);\n        if (!error_message.empty()) {\n          return DecodeImageResult(std::move(error_message));\n        }\n      }\n    } else {\n      wuffs_base__io_buffer empty = wuffs_base__empty_io_buffer();\n      wuffs_base__more_information minfo = wuffs_base__empty_more_information();\n      wuffs_base__status tmm_status =\n          image_decoder->tell_me_more(&empty, &minfo, &io_buf);\n      if (tmm_status.repr != nullptr) {\n        return DecodeImageResult(tmm_status.message());\n      }\n      if (minf" +
-	"o.flavor != WUFFS_BASE__MORE_INFORMATION__FLAVOR__IO_REDIRECT) {\n        return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n      }\n      uint64_t pos = minfo.io_redirect__range().min_incl;\n      std::string error_message = DecodeImageAdvanceIOBuf(\n          input, io_buf, !input.BringsItsOwnIOBuffer(), start_pos, pos);\n      if (!error_message.empty()) {\n        return DecodeImageResult(std::move(error_message));\n      }\n      fourcc = (int32_t)(minfo.io_redirect__fourcc());\n      if (fourcc == 0) {\n        return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n      }\n      image_decoder.reset();\n    }\n\n    // Make the image decoder.\n    image_decoder = callbacks.OnImageFormat(\n        (uint32_t)fourcc,\n        fourcc ? wuffs_base__empty_slice_u8() : io_buf.reader_slice());\n    if (!image_decoder) {\n      return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n    }\n\n    // Decode the image config.\n    while (true) {\n      wuffs_base__status id_dic_status =\n          image_decoder->d" +
-	"ecode_image_config(&image_config, &io_buf);\n      if (id_dic_status.repr == nullptr) {\n        break;\n      } else if (id_dic_status.repr == wuffs_base__note__i_o_redirect) {\n        if (redirected) {\n          return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n        }\n        redirected = true;\n        goto redirect;\n      } else if (id_dic_status.repr != wuffs_base__suspension__short_read) {\n        return DecodeImageResult(id_dic_status.message());\n      } else if (io_buf.meta.closed) {\n        return DecodeImageResult(DecodeImage_UnexpectedEndOfFile);\n      } else {\n        std::string error_message = input.CopyIn(&io_buf);\n        if (!error_message.empty()) {\n          return DecodeImageResult(std::move(error_message));\n        }\n      }\n    }\n  } while (false);\n\n  // Apply the override pixel format.\n  uint32_t w = image_config.pixcfg.width();\n  uint32_t h = image_config.pixcfg.height();\n  if ((w > max_incl_dimension) || (h > max_incl_dimension)) {\n    return DecodeImageResult(DecodeImage_M" +
-	"axInclDimensionExceeded);\n  }\n  if (override_pixel_format_repr != 0) {\n    image_config.pixcfg.set(override_pixel_format_repr,\n                            WUFFS_BASE__PIXEL_SUBSAMPLING__NONE, w, h);\n  }\n\n  // Allocate the pixel buffer.\n  uint64_t pixbuf_len_min_incl = 0;\n  if ((w > 0) && (h > 0)) {\n    pixbuf_len_min_incl = image_config.pixcfg.pixbuf_len();\n    if (pixbuf_len_min_incl == 0) {\n      return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);\n    }\n  }\n  bool valid_background_color =\n      wuffs_base__color_u32_argb_premul__is_valid(background_color);\n  DecodeImageCallbacks::AllocResult oic_result =\n      callbacks.OnImageConfig(image_config, valid_background_color);\n  if (!oic_result.error_message.empty()) {\n    return DecodeImageResult(std::move(oic_result.error_message));\n  } else if (oic_result.mem_slice.len < pixbuf_len_min_incl) {\n    return DecodeImageResult(DecodeImage_BufferIsTooShort);\n  }\n  wuffs_base__pixel_buffer pixel_buffer;\n  wuffs_base__status pb_sfs_status =\n      pixel_buff" +
-	"er.set_from_slice(&image_config.pixcfg, oic_result.mem_slice);\n  if (!pb_sfs_status.is_ok()) {\n    return DecodeImageResult(pb_sfs_status.message());\n  }\n  if (valid_background_color) {\n    wuffs_base__status pb_scufr_status = pixel_buffer.set_color_u32_fill_rect(\n        pixel_buffer.pixcfg.bounds(), background_color);\n    if (pb_scufr_status.repr != nullptr) {\n      return DecodeImageResult(pb_scufr_status.message());\n    }\n  }\n\n  // Allocate the work buffer. Wuffs' decoders conventionally assume that this\n  // can be uninitialized memory.\n  wuffs_base__range_ii_u64 workbuf_len = image_decoder->workbuf_len();\n  DecodeImageCallbacks::AllocResult alloc_workbuf_result =\n      callbacks.AllocWorkbuf(workbuf_len, true);\n  if (!alloc_workbuf_result.error_message.empty()) {\n    return DecodeImageResult(std::move(alloc_workbuf_result.error_message));\n  } else if (alloc_workbuf_result.mem_slice.len < workbuf_len.min_incl) {\n    return DecodeImageResult(DecodeImage_BufferIsTooShort);\n  }\n\n  // Decode the frame config" +
-	".\n  wuffs_base__frame_config frame_config = wuffs_base__null_frame_config();\n  while (true) {\n    wuffs_base__status id_dfc_status =\n        image_decoder->decode_frame_config(&frame_config, &io_buf);\n    if (id_dfc_status.repr == nullptr) {\n      break;\n    } else if (id_dfc_status.repr != wuffs_base__suspension__short_read) {\n      return DecodeImageResult(id_dfc_status.message());\n    } else if (io_buf.meta.closed) {\n      return DecodeImageResult(DecodeImage_UnexpectedEndOfFile);\n    } else {\n      std::string error_message = input.CopyIn(&io_buf);\n      if (!error_message.empty()) {\n        return DecodeImageResult(std::move(error_message));\n      }\n    }\n  }\n\n  // Decode the frame (the pixels).\n  //\n  // From here on, always returns the pixel_buffer. If we get this far, we can\n  // still display a partial image, even if we encounter an error.\n  std::string message(\"\");\n  if ((pixel_blend == WUFFS_BASE__PIXEL_BLEND__SRC_OVER) &&\n      frame_config.overwrite_instead_of_blend()) {\n    pixel_blend = WUFFS_B" +
-	"ASE__PIXEL_BLEND__SRC;\n  }\n  while (true) {\n    wuffs_base__status id_df_status =\n        image_decoder->decode_frame(&pixel_buffer, &io_buf, pixel_blend,\n                                    alloc_workbuf_result.mem_slice, nullptr);\n    if (id_df_status.repr == nullptr) {\n      break;\n    } else if (id_df_status.repr != wuffs_base__suspension__short_read) {\n      message = id_df_status.message();\n      break;\n    } else if (io_buf.meta.closed) {\n      message = DecodeImage_UnexpectedEndOfFile;\n      break;\n    } else {\n      std::string error_message = input.CopyIn(&io_buf);\n      if (!error_message.empty()) {\n        message = std::move(error_message);\n        break;\n      }\n    }\n  }\n  return DecodeImageResult(std::move(oic_result.mem_owner),\n                           oic_result.mem_slice, pixel_buffer,\n                           std::move(message));\n}\n\n}  // namespace\n\nDecodeImageResult  //\nDecodeImage(DecodeImageCallbacks& callbacks,\n            sync_io::Input& input,\n            uint32_t override_pixel_" +
-	"format_repr,\n            wuffs_base__pixel_blend pixel_blend,\n            wuffs_base__color_u32_argb_premul background_color,\n            uint32_t max_incl_dimension) {\n  wuffs_base__io_buffer* io_buf = input.BringsItsOwnIOBuffer();\n  wuffs_base__io_buffer fallback_io_buf = wuffs_base__empty_io_buffer();\n  std::unique_ptr<uint8_t[]> fallback_io_array(nullptr);\n  if (!io_buf) {\n    fallback_io_array = std::unique_ptr<uint8_t[]>(new uint8_t[32768]);\n    fallback_io_buf =\n        wuffs_base__ptr_u8__writer(fallback_io_array.get(), 32768);\n    io_buf = &fallback_io_buf;\n  }\n\n  wuffs_base__image_decoder::unique_ptr image_decoder(nullptr, &free);\n  DecodeImageResult result = DecodeImage0(\n      image_decoder, callbacks, input, *io_buf, override_pixel_format_repr,\n      pixel_blend, background_color, max_incl_dimension);\n  callbacks.Done(result, input, *io_buf, std::move(image_decoder));\n  return result;\n}\n\n}  // namespace wuffs_aux\n\n#endif  // !defined(WUFFS_CONFIG__MODULES) ||\n        // defined(WUFFS_CONFIG__MODU" +
-	"LE__AUX__IMAGE)\n" +
+	"           DecodeImageCallbacks& callbacks,\n             sync_io::Input& input,\n             wuffs_base__io_buffer& io_buf,\n             wuffs_base__pixel_blend pixel_blend,\n             wuffs_base__color_u32_argb_premul background_color,\n             uint32_t max_incl_dimension) {\n  // Check args.\n  switch (pixel_blend) {\n    case WUFFS_BASE__PIXEL_BLEND__SRC:\n    case WUFFS_BASE__PIXEL_BLEND__SRC_OVER:\n      break;\n    default:\n      return DecodeImageResult(DecodeImage_UnsupportedPixelBlend);\n  }\n\n  wuffs_base__image_config image_config = wuffs_base__null_image_config();\n  uint64_t start_pos = io_buf.reader_position();\n  bool redirected = false;\n  int32_t fourcc = 0;\nredirect:\n  do {\n    // Determine the image format.\n    if (!redirected) {\n      while (true) {\n        fourcc = wuffs_base__magic_number_guess_fourcc(io_buf.reader_slice());\n        if (fourcc > 0) {\n          break;\n        } else if ((fourcc == 0) && (io_buf.reader_length() >= 64)) {\n          break;\n        } else if (io_buf.meta.closed ||" +
+	" (io_buf.writer_length() == 0)) {\n          fourcc = 0;\n          break;\n        }\n        std::string error_message = input.CopyIn(&io_buf);\n        if (!error_message.empty()) {\n          return DecodeImageResult(std::move(error_message));\n        }\n      }\n    } else {\n      wuffs_base__io_buffer empty = wuffs_base__empty_io_buffer();\n      wuffs_base__more_information minfo = wuffs_base__empty_more_information();\n      wuffs_base__status tmm_status =\n          image_decoder->tell_me_more(&empty, &minfo, &io_buf);\n      if (tmm_status.repr != nullptr) {\n        return DecodeImageResult(tmm_status.message());\n      }\n      if (minfo.flavor != WUFFS_BASE__MORE_INFORMATION__FLAVOR__IO_REDIRECT) {\n        return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n      }\n      uint64_t pos = minfo.io_redirect__range().min_incl;\n      std::string error_message = DecodeImageAdvanceIOBuf(\n          input, io_buf, !input.BringsItsOwnIOBuffer(), start_pos, pos);\n      if (!error_message.empty()) {\n        return" +
+	" DecodeImageResult(std::move(error_message));\n      }\n      fourcc = (int32_t)(minfo.io_redirect__fourcc());\n      if (fourcc == 0) {\n        return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n      }\n      image_decoder.reset();\n    }\n\n    // Select the image decoder.\n    image_decoder = callbacks.SelectDecoder(\n        (uint32_t)fourcc,\n        fourcc ? wuffs_base__empty_slice_u8() : io_buf.reader_slice());\n    if (!image_decoder) {\n      return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n    }\n\n    // Decode the image config.\n    while (true) {\n      wuffs_base__status id_dic_status =\n          image_decoder->decode_image_config(&image_config, &io_buf);\n      if (id_dic_status.repr == nullptr) {\n        break;\n      } else if (id_dic_status.repr == wuffs_base__note__i_o_redirect) {\n        if (redirected) {\n          return DecodeImageResult(DecodeImage_UnsupportedImageFormat);\n        }\n        redirected = true;\n        goto redirect;\n      } else if (id_dic_status.repr != wuffs_bas" +
+	"e__suspension__short_read) {\n        return DecodeImageResult(id_dic_status.message());\n      } else if (io_buf.meta.closed) {\n        return DecodeImageResult(DecodeImage_UnexpectedEndOfFile);\n      } else {\n        std::string error_message = input.CopyIn(&io_buf);\n        if (!error_message.empty()) {\n          return DecodeImageResult(std::move(error_message));\n        }\n      }\n    }\n  } while (false);\n\n  // Select the pixel format.\n  uint32_t w = image_config.pixcfg.width();\n  uint32_t h = image_config.pixcfg.height();\n  if ((w > max_incl_dimension) || (h > max_incl_dimension)) {\n    return DecodeImageResult(DecodeImage_MaxInclDimensionExceeded);\n  }\n  wuffs_base__pixel_format pixel_format = callbacks.SelectPixfmt(image_config);\n  if (pixel_format.repr != image_config.pixcfg.pixel_format().repr) {\n    switch (pixel_format.repr) {\n      case WUFFS_BASE__PIXEL_FORMAT__BGR_565:\n      case WUFFS_BASE__PIXEL_FORMAT__BGR:\n      case WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL:\n      case WUFFS_BASE__PIXEL_FORMAT" +
+	"__BGRA_PREMUL:\n        break;\n      default:\n        return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);\n    }\n    image_config.pixcfg.set(pixel_format.repr,\n                            WUFFS_BASE__PIXEL_SUBSAMPLING__NONE, w, h);\n  }\n\n  // Allocate the pixel buffer.\n  uint64_t pixbuf_len_min_incl = 0;\n  if ((w > 0) && (h > 0)) {\n    pixbuf_len_min_incl = image_config.pixcfg.pixbuf_len();\n    if (pixbuf_len_min_incl == 0) {\n      return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);\n    }\n  }\n  bool valid_background_color =\n      wuffs_base__color_u32_argb_premul__is_valid(background_color);\n  DecodeImageCallbacks::AllocResult alloc_pixbuf_result =\n      callbacks.AllocPixbuf(image_config, valid_background_color);\n  if (!alloc_pixbuf_result.error_message.empty()) {\n    return DecodeImageResult(std::move(alloc_pixbuf_result.error_message));\n  } else if (alloc_pixbuf_result.mem_slice.len < pixbuf_len_min_incl) {\n    return DecodeImageResult(DecodeImage_BufferIsTooShort);\n  }\n  wuffs_base__pixel" +
+	"_buffer pixel_buffer;\n  wuffs_base__status pb_sfs_status = pixel_buffer.set_from_slice(\n      &image_config.pixcfg, alloc_pixbuf_result.mem_slice);\n  if (!pb_sfs_status.is_ok()) {\n    return DecodeImageResult(pb_sfs_status.message());\n  }\n  if (valid_background_color) {\n    wuffs_base__status pb_scufr_status = pixel_buffer.set_color_u32_fill_rect(\n        pixel_buffer.pixcfg.bounds(), background_color);\n    if (pb_scufr_status.repr != nullptr) {\n      return DecodeImageResult(pb_scufr_status.message());\n    }\n  }\n\n  // Allocate the work buffer. Wuffs' decoders conventionally assume that this\n  // can be uninitialized memory.\n  wuffs_base__range_ii_u64 workbuf_len = image_decoder->workbuf_len();\n  DecodeImageCallbacks::AllocResult alloc_workbuf_result =\n      callbacks.AllocWorkbuf(workbuf_len, true);\n  if (!alloc_workbuf_result.error_message.empty()) {\n    return DecodeImageResult(std::move(alloc_workbuf_result.error_message));\n  } else if (alloc_workbuf_result.mem_slice.len < workbuf_len.min_incl) {\n    retu" +
+	"rn DecodeImageResult(DecodeImage_BufferIsTooShort);\n  }\n\n  // Decode the frame config.\n  wuffs_base__frame_config frame_config = wuffs_base__null_frame_config();\n  while (true) {\n    wuffs_base__status id_dfc_status =\n        image_decoder->decode_frame_config(&frame_config, &io_buf);\n    if (id_dfc_status.repr == nullptr) {\n      break;\n    } else if (id_dfc_status.repr != wuffs_base__suspension__short_read) {\n      return DecodeImageResult(id_dfc_status.message());\n    } else if (io_buf.meta.closed) {\n      return DecodeImageResult(DecodeImage_UnexpectedEndOfFile);\n    } else {\n      std::string error_message = input.CopyIn(&io_buf);\n      if (!error_message.empty()) {\n        return DecodeImageResult(std::move(error_message));\n      }\n    }\n  }\n\n  // Decode the frame (the pixels).\n  //\n  // From here on, always returns the pixel_buffer. If we get this far, we can\n  // still display a partial image, even if we encounter an error.\n  std::string message(\"\");\n  if ((pixel_blend == WUFFS_BASE__PIXEL_BLEND__SRC_" +
+	"OVER) &&\n      frame_config.overwrite_instead_of_blend()) {\n    pixel_blend = WUFFS_BASE__PIXEL_BLEND__SRC;\n  }\n  while (true) {\n    wuffs_base__status id_df_status =\n        image_decoder->decode_frame(&pixel_buffer, &io_buf, pixel_blend,\n                                    alloc_workbuf_result.mem_slice, nullptr);\n    if (id_df_status.repr == nullptr) {\n      break;\n    } else if (id_df_status.repr != wuffs_base__suspension__short_read) {\n      message = id_df_status.message();\n      break;\n    } else if (io_buf.meta.closed) {\n      message = DecodeImage_UnexpectedEndOfFile;\n      break;\n    } else {\n      std::string error_message = input.CopyIn(&io_buf);\n      if (!error_message.empty()) {\n        message = std::move(error_message);\n        break;\n      }\n    }\n  }\n  return DecodeImageResult(std::move(alloc_pixbuf_result.mem_owner),\n                           alloc_pixbuf_result.mem_slice, pixel_buffer,\n                           std::move(message));\n}\n\n}  // namespace\n\nDecodeImageResult  //\nDecodeImage(D" +
+	"ecodeImageCallbacks& callbacks,\n            sync_io::Input& input,\n            wuffs_base__pixel_blend pixel_blend,\n            wuffs_base__color_u32_argb_premul background_color,\n            uint32_t max_incl_dimension) {\n  wuffs_base__io_buffer* io_buf = input.BringsItsOwnIOBuffer();\n  wuffs_base__io_buffer fallback_io_buf = wuffs_base__empty_io_buffer();\n  std::unique_ptr<uint8_t[]> fallback_io_array(nullptr);\n  if (!io_buf) {\n    fallback_io_array = std::unique_ptr<uint8_t[]>(new uint8_t[32768]);\n    fallback_io_buf =\n        wuffs_base__ptr_u8__writer(fallback_io_array.get(), 32768);\n    io_buf = &fallback_io_buf;\n  }\n\n  wuffs_base__image_decoder::unique_ptr image_decoder(nullptr, &free);\n  DecodeImageResult result =\n      DecodeImage0(image_decoder, callbacks, input, *io_buf, pixel_blend,\n                   background_color, max_incl_dimension);\n  callbacks.Done(result, input, *io_buf, std::move(image_decoder));\n  return result;\n}\n\n}  // namespace wuffs_aux\n\n#endif  // !defined(WUFFS_CONFIG__MODULES) ||" +
+	"\n        // defined(WUFFS_CONFIG__MODULE__AUX__IMAGE)\n" +
 	""
 
 const AuxImageHh = "" +
-	"// ---------------- Auxiliary - Image\n\nnamespace wuffs_aux {\n\nstruct DecodeImageResult {\n  DecodeImageResult(MemOwner&& pixbuf_mem_owner0,\n                    wuffs_base__slice_u8 pixbuf_mem_slice0,\n                    wuffs_base__pixel_buffer pixbuf0,\n                    std::string&& error_message0);\n  DecodeImageResult(std::string&& error_message0);\n\n  MemOwner pixbuf_mem_owner;\n  wuffs_base__slice_u8 pixbuf_mem_slice;\n  wuffs_base__pixel_buffer pixbuf;\n  std::string error_message;\n};\n\n// DecodeImageCallbacks are the callbacks given to DecodeImage. They are always\n// called in this order:\n//  1. OnImageFormat\n//  2. OnImageConfig\n//  3. AllocWorkbuf\n//  4. Done\n//\n// It may return early - the third callback might not be invoked if the second\n// one fails (returns a non-empty error message) - but the final callback\n// (Done) is always invoked.\nclass DecodeImageCallbacks {\n public:\n  // AllocResult holds a memory allocation (the result of malloc or new, a\n  // statically allocated pointer, etc), or an error " +
-	"message. The memory is\n  // de-allocated when mem_owner goes out of scope and is destroyed.\n  struct AllocResult {\n    AllocResult(MemOwner&& mem_owner0, wuffs_base__slice_u8 mem_slice0);\n    AllocResult(std::string&& error_message0);\n\n    MemOwner mem_owner;\n    wuffs_base__slice_u8 mem_slice;\n    std::string error_message;\n  };\n\n  // OnImageFormat returns the image decoder for the input data's file format.\n  // Returning a nullptr means failure (DecodeImage_UnsupportedImageFormat).\n  //\n  // Common formats will have a FourCC value in the range [1 ..= 0x7FFF_FFFF],\n  // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that the\n  // caller is responsible for examining the opening bytes (a prefix) of the\n  // input data. OnImageFormat implementations should not modify those bytes.\n  //\n  // OnImageFormat might be called more than once, since some image file\n  // formats can wrap others. For example, a nominal BMP file can actually\n  // contain a JPEG or a PNG.\n  //\n  // The default OnImageFormat acc" +
-	"epts the FOURCC codes listed below. For\n  // modular builds (i.e. when #define'ing WUFFS_CONFIG__MODULES), acceptance\n  // of the ETC file format is optional (for each value of ETC) and depends on\n  // the corresponding module to be enabled at compile time (i.e. #define'ing\n  // WUFFS_CONFIG__MODULE__ETC).\n  //  - WUFFS_BASE__FOURCC__BMP\n  //  - WUFFS_BASE__FOURCC__GIF\n  //  - WUFFS_BASE__FOURCC__NIE\n  //  - WUFFS_BASE__FOURCC__PNG\n  //  - WUFFS_BASE__FOURCC__WBMP\n  virtual wuffs_base__image_decoder::unique_ptr  //\n  OnImageFormat(uint32_t fourcc, wuffs_base__slice_u8 prefix);\n\n  // OnImageConfig allocates the pixel buffer.\n  //\n  // allow_uninitialized_memory will be true if a valid background_color was\n  // passed to DecodeImage, since the pixel buffer's contents will be\n  // overwritten with that color after OnImageConfig returns.\n  //\n  // The default OnImageConfig implementation allocates either uninitialized or\n  // zeroed memory. Zeroed memory typically corresponds to filling with opaque\n  // black or " +
-	"transparent black, depending on the pixel format.\n  virtual AllocResult  //\n  OnImageConfig(const wuffs_base__image_config& image_config,\n                bool allow_uninitialized_memory);\n\n  // AllocWorkbuf allocates the work buffer. The allocated buffer's length\n  // should be at least len_range.min_incl, but larger allocations (up to\n  // len_range.max_incl) may have better performance (by using more memory).\n  //\n  // The default AllocWorkbuf implementation allocates len_range.max_incl bytes\n  // of either uninitialized or zeroed memory.\n  virtual AllocResult  //\n  AllocWorkbuf(wuffs_base__range_ii_u64 len_range,\n               bool allow_uninitialized_memory);\n\n  // Done is always the last Callback method called by DecodeImage, whether or\n  // not parsing the input encountered an error. Even when successful, trailing\n  // data may remain in input and buffer.\n  //\n  // The image_decoder is the one returned by OnImageFormat (if OnImageFormat\n  // was successful), or a no-op unique_ptr otherwise. Like any un" +
-	"ique_ptr,\n  // ownership moves to the Done implementation.\n  //\n  // Do not keep a reference to buffer or buffer.data.ptr after Done returns,\n  // as DecodeImage may then de-allocate the backing array.\n  //\n  // The default Done implementation is a no-op, other than running the\n  // image_decoder unique_ptr destructor.\n  virtual void  //\n  Done(DecodeImageResult& result,\n       sync_io::Input& input,\n       IOBuffer& buffer,\n       wuffs_base__image_decoder::unique_ptr image_decoder);\n};\n\nextern const char DecodeImage_BufferIsTooShort[];\nextern const char DecodeImage_MaxInclDimensionExceeded[];\nextern const char DecodeImage_OutOfMemory[];\nextern const char DecodeImage_UnexpectedEndOfFile[];\nextern const char DecodeImage_UnsupportedImageFormat[];\nextern const char DecodeImage_UnsupportedPixelBlend[];\nextern const char DecodeImage_UnsupportedPixelConfiguration[];\nextern const char DecodeImage_UnsupportedPixelFormat[];\n\n// DecodeImage decodes the image data in input. A variety of image file formats\n// can be dec" +
-	"oded, depending on what callbacks.OnImageFormat returns.\n//\n// For animated formats, only the first frame is returned, since the API is\n// simpler for synchronous I/O and having DecodeImage only return when\n// completely done, but rendering animation often involves handling other\n// events in between animation frames. To decode multiple frames of animated\n// images, or for asynchronous I/O (e.g. when decoding an image streamed over\n// the network), use Wuffs' lower level C API instead of its higher level,\n// simplified C++ API (the wuffs_aux API).\n//\n// The DecodeImageResult's fields depend on whether decoding succeeded:\n//  - On total success, the error_message is empty and pixbuf.pixcfg.is_valid()\n//    is true.\n//  - On partial success (e.g. the input file was truncated but we are still\n//    able to decode some of the pixels), error_message is non-empty but\n//    pixbuf.pixcfg.is_valid() is still true. It is up to the caller whether to\n//    accept or reject partial success.\n//  - On failure, the error_me" +
-	"ssage is non_empty and pixbuf.pixcfg.is_valid()\n//    is false.\n//\n// The callbacks allocate the pixel buffer memory and work buffer memory. On\n// success, pixel buffer memory ownership is passed to the DecodeImage caller\n// as the returned pixbuf_mem_owner. Regardless of success or failure, the work\n// buffer memory is deleted.\n//\n// If override_pixel_format_repr is zero then the pixel buffer will have the\n// image file's natural pixel format. For example, GIF images' natural pixel\n// format is an indexed one.\n//\n// If override_pixel_format_repr is non-zero (and one of the constants listed\n// below) then the image will be decoded to that particular pixel format:\n//  - WUFFS_BASE__PIXEL_FORMAT__BGR_565\n//  - WUFFS_BASE__PIXEL_FORMAT__BGR\n//  - WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL\n//  - WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL\n//\n// The pixel_blend (one of the constants listed below) determines how to\n// composite the decoded image over the pixel buffer's original pixels (as\n// returned by callbacks.OnImageCo" +
-	"nfig):\n//  - WUFFS_BASE__PIXEL_BLEND__SRC\n//  - WUFFS_BASE__PIXEL_BLEND__SRC_OVER\n//\n// The background_color is used to fill the pixel buffer after\n// callbacks.OnImageConfig returns, if it is valid in the\n// wuffs_base__color_u32_argb_premul__is_valid sense. The default value,\n// 0x0000_0001, is not valid since its Blue channel value (0x01) is greater\n// than its Alpha channel value (0x00). A valid background_color will typically\n// be overwritten when pixel_blend is WUFFS_BASE__PIXEL_BLEND__SRC, but might\n// still be visible on partial (not total) success or when pixel_blend is\n// WUFFS_BASE__PIXEL_BLEND__SRC_OVER and the decoded image is not fully opaque.\n//\n// Decoding fails (with DecodeImage_MaxInclDimensionExceeded) if the image's\n// width or height is greater than max_incl_dimension.\nDecodeImageResult  //\nDecodeImage(DecodeImageCallbacks& callbacks,\n            sync_io::Input& input,\n            uint32_t override_pixel_format_repr,\n            wuffs_base__pixel_blend pixel_blend = WUFFS_BASE__PIXEL_BLE" +
-	"ND__SRC,\n            wuffs_base__color_u32_argb_premul background_color = 1,  // Invalid.\n            uint32_t max_incl_dimension = 1048575);  // 0x000F_FFFF\n\n}  // namespace wuffs_aux\n" +
+	"// ---------------- Auxiliary - Image\n\nnamespace wuffs_aux {\n\nstruct DecodeImageResult {\n  DecodeImageResult(MemOwner&& pixbuf_mem_owner0,\n                    wuffs_base__slice_u8 pixbuf_mem_slice0,\n                    wuffs_base__pixel_buffer pixbuf0,\n                    std::string&& error_message0);\n  DecodeImageResult(std::string&& error_message0);\n\n  MemOwner pixbuf_mem_owner;\n  wuffs_base__slice_u8 pixbuf_mem_slice;\n  wuffs_base__pixel_buffer pixbuf;\n  std::string error_message;\n};\n\n// DecodeImageCallbacks are the callbacks given to DecodeImage. They are always\n// called in this order:\n//  1. SelectDecoder\n//  2. SelectPixfmt\n//  3. AllocPixbuf\n//  4. AllocWorkbuf\n//  5. Done\n//\n// It may return early - the third callback might not be invoked if the second\n// one fails - but the final callback (Done) is always invoked.\nclass DecodeImageCallbacks {\n public:\n  // AllocResult holds a memory allocation (the result of malloc or new, a\n  // statically allocated pointer, etc), or an error message. The memory i" +
+	"s\n  // de-allocated when mem_owner goes out of scope and is destroyed.\n  struct AllocResult {\n    AllocResult(MemOwner&& mem_owner0, wuffs_base__slice_u8 mem_slice0);\n    AllocResult(std::string&& error_message0);\n\n    MemOwner mem_owner;\n    wuffs_base__slice_u8 mem_slice;\n    std::string error_message;\n  };\n\n  // SelectDecoder returns the image decoder for the input data's file format.\n  // Returning a nullptr means failure (DecodeImage_UnsupportedImageFormat).\n  //\n  // Common formats will have a FourCC value in the range [1 ..= 0x7FFF_FFFF],\n  // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that the\n  // caller is responsible for examining the opening bytes (a prefix) of the\n  // input data. SelectDecoder implementations should not modify those bytes.\n  //\n  // SelectDecoder might be called more than once, since some image file\n  // formats can wrap others. For example, a nominal BMP file can actually\n  // contain a JPEG or a PNG.\n  //\n  // The default SelectDecoder accepts the FOURCC codes" +
+	" listed below. For\n  // modular builds (i.e. when #define'ing WUFFS_CONFIG__MODULES), acceptance\n  // of the ETC file format is optional (for each value of ETC) and depends on\n  // the corresponding module to be enabled at compile time (i.e. #define'ing\n  // WUFFS_CONFIG__MODULE__ETC).\n  //  - WUFFS_BASE__FOURCC__BMP\n  //  - WUFFS_BASE__FOURCC__GIF\n  //  - WUFFS_BASE__FOURCC__NIE\n  //  - WUFFS_BASE__FOURCC__PNG\n  //  - WUFFS_BASE__FOURCC__WBMP\n  virtual wuffs_base__image_decoder::unique_ptr  //\n  SelectDecoder(uint32_t fourcc, wuffs_base__slice_u8 prefix);\n\n  // SelectPixfmt returns the destination pixel format for AllocPixbuf. It\n  // should return wuffs_base__make_pixel_format(etc) called with one of:\n  //  - WUFFS_BASE__PIXEL_FORMAT__BGR_565\n  //  - WUFFS_BASE__PIXEL_FORMAT__BGR\n  //  - WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL\n  //  - WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL\n  // or return image_config.pixcfg.pixel_format(). The latter means to use the\n  // image file's natural pixel format. For example, GIF " +
+	"images' natural pixel\n  // format is an indexed one.\n  //\n  // Returning otherwise means failure (DecodeImage_UnsupportedPixelFormat).\n  //\n  // The default SelectPixfmt implementation returns\n  // wuffs_base__make_pixel_format(WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL)\n  // which is 4 bytes per pixel (8 bits per channel × 4 channels).\n  virtual wuffs_base__pixel_format  //\n  SelectPixfmt(const wuffs_base__image_config& image_config);\n\n  // AllocPixbuf allocates the pixel buffer.\n  //\n  // allow_uninitialized_memory will be true if a valid background_color was\n  // passed to DecodeImage, since the pixel buffer's contents will be\n  // overwritten with that color after AllocPixbuf returns.\n  //\n  // The default AllocPixbuf implementation allocates either uninitialized or\n  // zeroed memory. Zeroed memory typically corresponds to filling with opaque\n  // black or transparent black, depending on the pixel format.\n  virtual AllocResult  //\n  AllocPixbuf(const wuffs_base__image_config& image_config,\n              b" +
+	"ool allow_uninitialized_memory);\n\n  // AllocWorkbuf allocates the work buffer. The allocated buffer's length\n  // should be at least len_range.min_incl, but larger allocations (up to\n  // len_range.max_incl) may have better performance (by using more memory).\n  //\n  // The default AllocWorkbuf implementation allocates len_range.max_incl bytes\n  // of either uninitialized or zeroed memory.\n  virtual AllocResult  //\n  AllocWorkbuf(wuffs_base__range_ii_u64 len_range,\n               bool allow_uninitialized_memory);\n\n  // Done is always the last Callback method called by DecodeImage, whether or\n  // not parsing the input encountered an error. Even when successful, trailing\n  // data may remain in input and buffer.\n  //\n  // The image_decoder is the one returned by SelectDecoder (if SelectDecoder\n  // was successful), or a no-op unique_ptr otherwise. Like any unique_ptr,\n  // ownership moves to the Done implementation.\n  //\n  // Do not keep a reference to buffer or buffer.data.ptr after Done returns,\n  // as Decod" +
+	"eImage may then de-allocate the backing array.\n  //\n  // The default Done implementation is a no-op, other than running the\n  // image_decoder unique_ptr destructor.\n  virtual void  //\n  Done(DecodeImageResult& result,\n       sync_io::Input& input,\n       IOBuffer& buffer,\n       wuffs_base__image_decoder::unique_ptr image_decoder);\n};\n\nextern const char DecodeImage_BufferIsTooShort[];\nextern const char DecodeImage_MaxInclDimensionExceeded[];\nextern const char DecodeImage_OutOfMemory[];\nextern const char DecodeImage_UnexpectedEndOfFile[];\nextern const char DecodeImage_UnsupportedImageFormat[];\nextern const char DecodeImage_UnsupportedPixelBlend[];\nextern const char DecodeImage_UnsupportedPixelConfiguration[];\nextern const char DecodeImage_UnsupportedPixelFormat[];\n\n// DecodeImage decodes the image data in input. A variety of image file formats\n// can be decoded, depending on what callbacks.SelectDecoder returns.\n//\n// For animated formats, only the first frame is returned, since the API is\n// simpler for sync" +
+	"hronous I/O and having DecodeImage only return when\n// completely done, but rendering animation often involves handling other\n// events in between animation frames. To decode multiple frames of animated\n// images, or for asynchronous I/O (e.g. when decoding an image streamed over\n// the network), use Wuffs' lower level C API instead of its higher level,\n// simplified C++ API (the wuffs_aux API).\n//\n// The DecodeImageResult's fields depend on whether decoding succeeded:\n//  - On total success, the error_message is empty and pixbuf.pixcfg.is_valid()\n//    is true.\n//  - On partial success (e.g. the input file was truncated but we are still\n//    able to decode some of the pixels), error_message is non-empty but\n//    pixbuf.pixcfg.is_valid() is still true. It is up to the caller whether to\n//    accept or reject partial success.\n//  - On failure, the error_message is non_empty and pixbuf.pixcfg.is_valid()\n//    is false.\n//\n// The callbacks allocate the pixel buffer memory and work buffer memory. On\n// success," +
+	" pixel buffer memory ownership is passed to the DecodeImage caller\n// as the returned pixbuf_mem_owner. Regardless of success or failure, the work\n// buffer memory is deleted.\n//\n// The pixel_blend (one of the constants listed below) determines how to\n// composite the decoded image over the pixel buffer's original pixels (as\n// returned by callbacks.AllocPixbuf):\n//  - WUFFS_BASE__PIXEL_BLEND__SRC\n//  - WUFFS_BASE__PIXEL_BLEND__SRC_OVER\n//\n// The background_color is used to fill the pixel buffer after\n// callbacks.AllocPixbuf returns, if it is valid in the\n// wuffs_base__color_u32_argb_premul__is_valid sense. The default value,\n// 0x0000_0001, is not valid since its Blue channel value (0x01) is greater\n// than its Alpha channel value (0x00). A valid background_color will typically\n// be overwritten when pixel_blend is WUFFS_BASE__PIXEL_BLEND__SRC, but might\n// still be visible on partial (not total) success or when pixel_blend is\n// WUFFS_BASE__PIXEL_BLEND__SRC_OVER and the decoded image is not fully opaque.\n" +
+	"//\n// Decoding fails (with DecodeImage_MaxInclDimensionExceeded) if the image's\n// width or height is greater than max_incl_dimension.\nDecodeImageResult  //\nDecodeImage(DecodeImageCallbacks& callbacks,\n            sync_io::Input& input,\n            wuffs_base__pixel_blend pixel_blend = WUFFS_BASE__PIXEL_BLEND__SRC,\n            wuffs_base__color_u32_argb_premul background_color = 1,  // Invalid.\n            uint32_t max_incl_dimension = 1048575);  // 0x000F_FFFF\n\n}  // namespace wuffs_aux\n" +
 	""
 
 const AuxJsonCc = "" +
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 75aab2e..d12ea43 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -9469,14 +9469,14 @@
 
 // DecodeImageCallbacks are the callbacks given to DecodeImage. They are always
 // called in this order:
-//  1. OnImageFormat
-//  2. OnImageConfig
-//  3. AllocWorkbuf
-//  4. Done
+//  1. SelectDecoder
+//  2. SelectPixfmt
+//  3. AllocPixbuf
+//  4. AllocWorkbuf
+//  5. Done
 //
 // It may return early - the third callback might not be invoked if the second
-// one fails (returns a non-empty error message) - but the final callback
-// (Done) is always invoked.
+// one fails - but the final callback (Done) is always invoked.
 class DecodeImageCallbacks {
  public:
   // AllocResult holds a memory allocation (the result of malloc or new, a
@@ -9491,19 +9491,19 @@
     std::string error_message;
   };
 
-  // OnImageFormat returns the image decoder for the input data's file format.
+  // SelectDecoder returns the image decoder for the input data's file format.
   // Returning a nullptr means failure (DecodeImage_UnsupportedImageFormat).
   //
   // Common formats will have a FourCC value in the range [1 ..= 0x7FFF_FFFF],
   // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that the
   // caller is responsible for examining the opening bytes (a prefix) of the
-  // input data. OnImageFormat implementations should not modify those bytes.
+  // input data. SelectDecoder implementations should not modify those bytes.
   //
-  // OnImageFormat might be called more than once, since some image file
+  // SelectDecoder might be called more than once, since some image file
   // formats can wrap others. For example, a nominal BMP file can actually
   // contain a JPEG or a PNG.
   //
-  // The default OnImageFormat accepts the FOURCC codes listed below. For
+  // The default SelectDecoder accepts the FOURCC codes listed below. For
   // modular builds (i.e. when #define'ing WUFFS_CONFIG__MODULES), acceptance
   // of the ETC file format is optional (for each value of ETC) and depends on
   // the corresponding module to be enabled at compile time (i.e. #define'ing
@@ -9514,20 +9514,38 @@
   //  - WUFFS_BASE__FOURCC__PNG
   //  - WUFFS_BASE__FOURCC__WBMP
   virtual wuffs_base__image_decoder::unique_ptr  //
-  OnImageFormat(uint32_t fourcc, wuffs_base__slice_u8 prefix);
+  SelectDecoder(uint32_t fourcc, wuffs_base__slice_u8 prefix);
 
-  // OnImageConfig allocates the pixel buffer.
+  // SelectPixfmt returns the destination pixel format for AllocPixbuf. It
+  // should return wuffs_base__make_pixel_format(etc) called with one of:
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGR_565
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGR
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL
+  //  - WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL
+  // or return image_config.pixcfg.pixel_format(). The latter means to use the
+  // image file's natural pixel format. For example, GIF images' natural pixel
+  // format is an indexed one.
+  //
+  // Returning otherwise means failure (DecodeImage_UnsupportedPixelFormat).
+  //
+  // The default SelectPixfmt implementation returns
+  // wuffs_base__make_pixel_format(WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL)
+  // which is 4 bytes per pixel (8 bits per channel × 4 channels).
+  virtual wuffs_base__pixel_format  //
+  SelectPixfmt(const wuffs_base__image_config& image_config);
+
+  // AllocPixbuf allocates the pixel buffer.
   //
   // allow_uninitialized_memory will be true if a valid background_color was
   // passed to DecodeImage, since the pixel buffer's contents will be
-  // overwritten with that color after OnImageConfig returns.
+  // overwritten with that color after AllocPixbuf returns.
   //
-  // The default OnImageConfig implementation allocates either uninitialized or
+  // The default AllocPixbuf implementation allocates either uninitialized or
   // zeroed memory. Zeroed memory typically corresponds to filling with opaque
   // black or transparent black, depending on the pixel format.
   virtual AllocResult  //
-  OnImageConfig(const wuffs_base__image_config& image_config,
-                bool allow_uninitialized_memory);
+  AllocPixbuf(const wuffs_base__image_config& image_config,
+              bool allow_uninitialized_memory);
 
   // AllocWorkbuf allocates the work buffer. The allocated buffer's length
   // should be at least len_range.min_incl, but larger allocations (up to
@@ -9543,7 +9561,7 @@
   // not parsing the input encountered an error. Even when successful, trailing
   // data may remain in input and buffer.
   //
-  // The image_decoder is the one returned by OnImageFormat (if OnImageFormat
+  // The image_decoder is the one returned by SelectDecoder (if SelectDecoder
   // was successful), or a no-op unique_ptr otherwise. Like any unique_ptr,
   // ownership moves to the Done implementation.
   //
@@ -9569,7 +9587,7 @@
 extern const char DecodeImage_UnsupportedPixelFormat[];
 
 // DecodeImage decodes the image data in input. A variety of image file formats
-// can be decoded, depending on what callbacks.OnImageFormat returns.
+// can be decoded, depending on what callbacks.SelectDecoder returns.
 //
 // For animated formats, only the first frame is returned, since the API is
 // simpler for synchronous I/O and having DecodeImage only return when
@@ -9594,25 +9612,14 @@
 // as the returned pixbuf_mem_owner. Regardless of success or failure, the work
 // buffer memory is deleted.
 //
-// If override_pixel_format_repr is zero then the pixel buffer will have the
-// image file's natural pixel format. For example, GIF images' natural pixel
-// format is an indexed one.
-//
-// If override_pixel_format_repr is non-zero (and one of the constants listed
-// below) then the image will be decoded to that particular pixel format:
-//  - WUFFS_BASE__PIXEL_FORMAT__BGR_565
-//  - WUFFS_BASE__PIXEL_FORMAT__BGR
-//  - WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL
-//  - WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL
-//
 // The pixel_blend (one of the constants listed below) determines how to
 // composite the decoded image over the pixel buffer's original pixels (as
-// returned by callbacks.OnImageConfig):
+// returned by callbacks.AllocPixbuf):
 //  - WUFFS_BASE__PIXEL_BLEND__SRC
 //  - WUFFS_BASE__PIXEL_BLEND__SRC_OVER
 //
 // The background_color is used to fill the pixel buffer after
-// callbacks.OnImageConfig returns, if it is valid in the
+// callbacks.AllocPixbuf returns, if it is valid in the
 // wuffs_base__color_u32_argb_premul__is_valid sense. The default value,
 // 0x0000_0001, is not valid since its Blue channel value (0x01) is greater
 // than its Alpha channel value (0x00). A valid background_color will typically
@@ -9625,7 +9632,6 @@
 DecodeImageResult  //
 DecodeImage(DecodeImageCallbacks& callbacks,
             sync_io::Input& input,
-            uint32_t override_pixel_format_repr,
             wuffs_base__pixel_blend pixel_blend = WUFFS_BASE__PIXEL_BLEND__SRC,
             wuffs_base__color_u32_argb_premul background_color = 1,  // Invalid.
             uint32_t max_incl_dimension = 1048575);  // 0x000F_FFFF
@@ -36910,7 +36916,7 @@
       error_message(std::move(error_message0)) {}
 
 wuffs_base__image_decoder::unique_ptr  //
-DecodeImageCallbacks::OnImageFormat(uint32_t fourcc,
+DecodeImageCallbacks::SelectDecoder(uint32_t fourcc,
                                     wuffs_base__slice_u8 prefix) {
   switch (fourcc) {
 #if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__BMP)
@@ -36946,10 +36952,16 @@
   return wuffs_base__image_decoder::unique_ptr(nullptr, &free);
 }
 
+wuffs_base__pixel_format  //
+DecodeImageCallbacks::SelectPixfmt(
+    const wuffs_base__image_config& image_config) {
+  return wuffs_base__make_pixel_format(
+      WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL);
+}
+
 DecodeImageCallbacks::AllocResult  //
-DecodeImageCallbacks::OnImageConfig(
-    const wuffs_base__image_config& image_config,
-    bool allow_uninitialized_memory) {
+DecodeImageCallbacks::AllocPixbuf(const wuffs_base__image_config& image_config,
+                                  bool allow_uninitialized_memory) {
   uint32_t w = image_config.pixcfg.width();
   uint32_t h = image_config.pixcfg.height();
   if ((w == 0) || (h == 0)) {
@@ -37047,21 +37059,10 @@
              DecodeImageCallbacks& callbacks,
              sync_io::Input& input,
              wuffs_base__io_buffer& io_buf,
-             uint32_t override_pixel_format_repr,
              wuffs_base__pixel_blend pixel_blend,
              wuffs_base__color_u32_argb_premul background_color,
              uint32_t max_incl_dimension) {
   // Check args.
-  switch (override_pixel_format_repr) {
-    case 0:
-    case WUFFS_BASE__PIXEL_FORMAT__BGR_565:
-    case WUFFS_BASE__PIXEL_FORMAT__BGR:
-    case WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL:
-    case WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL:
-      break;
-    default:
-      return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);
-  }
   switch (pixel_blend) {
     case WUFFS_BASE__PIXEL_BLEND__SRC:
     case WUFFS_BASE__PIXEL_BLEND__SRC_OVER:
@@ -37117,8 +37118,8 @@
       image_decoder.reset();
     }
 
-    // Make the image decoder.
-    image_decoder = callbacks.OnImageFormat(
+    // Select the image decoder.
+    image_decoder = callbacks.SelectDecoder(
         (uint32_t)fourcc,
         fourcc ? wuffs_base__empty_slice_u8() : io_buf.reader_slice());
     if (!image_decoder) {
@@ -37150,14 +37151,24 @@
     }
   } while (false);
 
-  // Apply the override pixel format.
+  // Select the pixel format.
   uint32_t w = image_config.pixcfg.width();
   uint32_t h = image_config.pixcfg.height();
   if ((w > max_incl_dimension) || (h > max_incl_dimension)) {
     return DecodeImageResult(DecodeImage_MaxInclDimensionExceeded);
   }
-  if (override_pixel_format_repr != 0) {
-    image_config.pixcfg.set(override_pixel_format_repr,
+  wuffs_base__pixel_format pixel_format = callbacks.SelectPixfmt(image_config);
+  if (pixel_format.repr != image_config.pixcfg.pixel_format().repr) {
+    switch (pixel_format.repr) {
+      case WUFFS_BASE__PIXEL_FORMAT__BGR_565:
+      case WUFFS_BASE__PIXEL_FORMAT__BGR:
+      case WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL:
+      case WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL:
+        break;
+      default:
+        return DecodeImageResult(DecodeImage_UnsupportedPixelFormat);
+    }
+    image_config.pixcfg.set(pixel_format.repr,
                             WUFFS_BASE__PIXEL_SUBSAMPLING__NONE, w, h);
   }
 
@@ -37171,16 +37182,16 @@
   }
   bool valid_background_color =
       wuffs_base__color_u32_argb_premul__is_valid(background_color);
-  DecodeImageCallbacks::AllocResult oic_result =
-      callbacks.OnImageConfig(image_config, valid_background_color);
-  if (!oic_result.error_message.empty()) {
-    return DecodeImageResult(std::move(oic_result.error_message));
-  } else if (oic_result.mem_slice.len < pixbuf_len_min_incl) {
+  DecodeImageCallbacks::AllocResult alloc_pixbuf_result =
+      callbacks.AllocPixbuf(image_config, valid_background_color);
+  if (!alloc_pixbuf_result.error_message.empty()) {
+    return DecodeImageResult(std::move(alloc_pixbuf_result.error_message));
+  } else if (alloc_pixbuf_result.mem_slice.len < pixbuf_len_min_incl) {
     return DecodeImageResult(DecodeImage_BufferIsTooShort);
   }
   wuffs_base__pixel_buffer pixel_buffer;
-  wuffs_base__status pb_sfs_status =
-      pixel_buffer.set_from_slice(&image_config.pixcfg, oic_result.mem_slice);
+  wuffs_base__status pb_sfs_status = pixel_buffer.set_from_slice(
+      &image_config.pixcfg, alloc_pixbuf_result.mem_slice);
   if (!pb_sfs_status.is_ok()) {
     return DecodeImageResult(pb_sfs_status.message());
   }
@@ -37251,8 +37262,8 @@
       }
     }
   }
-  return DecodeImageResult(std::move(oic_result.mem_owner),
-                           oic_result.mem_slice, pixel_buffer,
+  return DecodeImageResult(std::move(alloc_pixbuf_result.mem_owner),
+                           alloc_pixbuf_result.mem_slice, pixel_buffer,
                            std::move(message));
 }
 
@@ -37261,7 +37272,6 @@
 DecodeImageResult  //
 DecodeImage(DecodeImageCallbacks& callbacks,
             sync_io::Input& input,
-            uint32_t override_pixel_format_repr,
             wuffs_base__pixel_blend pixel_blend,
             wuffs_base__color_u32_argb_premul background_color,
             uint32_t max_incl_dimension) {
@@ -37276,9 +37286,9 @@
   }
 
   wuffs_base__image_decoder::unique_ptr image_decoder(nullptr, &free);
-  DecodeImageResult result = DecodeImage0(
-      image_decoder, callbacks, input, *io_buf, override_pixel_format_repr,
-      pixel_blend, background_color, max_incl_dimension);
+  DecodeImageResult result =
+      DecodeImage0(image_decoder, callbacks, input, *io_buf, pixel_blend,
+                   background_color, max_incl_dimension);
   callbacks.Done(result, input, *io_buf, std::move(image_decoder));
   return result;
 }