Fix dithering bug in merged 4:2:0/RGB565 algorithm
d0 should always be used for the first row, and d1 should always be used
for the second row.
Addresses concerns raised in #95, #81.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 46094cc..296e408 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -455,7 +455,7 @@
set(MD5_BMP_420_ISLOW_565 bf9d13e16c4923b92e1faa604d7922cb)
set(MD5_BMP_420_ISLOW_565D 6bde71526acc44bcff76f696df8638d2)
set(MD5_BMP_420M_ISLOW_565 8dc0185245353cfa32ad97027342216f)
- set(MD5_BMP_420M_ISLOW_565D d1be3a3339166255e76fa50a0d70d73e)
+ set(MD5_BMP_420M_ISLOW_565D ce034037d212bc403330df6f915c161b)
set(MD5_PPM_420_ISLOW_SKIP15_31 c4c65c1e43d7275cd50328a61e6534f0)
set(MD5_PPM_420_ISLOW_ARI_SKIP16_139 087c6b123db16ac00cb88c5b590bb74a)
set(MD5_PPM_420_ISLOW_PROG_CROP62x62_71_71 26eb36ccc7d1f0cb80cdabb0ac8b5d99)
diff --git a/ChangeLog.md b/ChangeLog.md
index e44ddc8..406c6db 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -7,6 +7,10 @@
pose a security threat, but removing the warnings makes it easier to detect
actual security issues, should they arise in the future.
+2. Fixed a bug in the merged 4:2:0 upsampling/dithered RGB565 color conversion
+algorithm that caused incorrect dithering in the output image. This algorithm
+now produces bitwise-identical results to the unmerged algorithms.
+
1.5.3
=====
diff --git a/Makefile.am b/Makefile.am
index 0c2d253..1d3d420 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -275,7 +275,7 @@
MD5_BMP_420_ISLOW_565 = bf9d13e16c4923b92e1faa604d7922cb
MD5_BMP_420_ISLOW_565D = 6bde71526acc44bcff76f696df8638d2
MD5_BMP_420M_ISLOW_565 = 8dc0185245353cfa32ad97027342216f
-MD5_BMP_420M_ISLOW_565D =d1be3a3339166255e76fa50a0d70d73e
+MD5_BMP_420M_ISLOW_565D = ce034037d212bc403330df6f915c161b
MD5_PPM_420_ISLOW_SKIP15_31 = c4c65c1e43d7275cd50328a61e6534f0
MD5_PPM_420_ISLOW_ARI_SKIP16_139 = 087c6b123db16ac00cb88c5b590bb74a
MD5_PPM_420_ISLOW_PROG_CROP62x62_71_71 = 26eb36ccc7d1f0cb80cdabb0ac8b5d99
diff --git a/jdmrg565.c b/jdmrg565.c
index 18287b3..a376340 100644
--- a/jdmrg565.c
+++ b/jdmrg565.c
@@ -5,7 +5,7 @@
* Copyright (C) 1994-1996, Thomas G. Lane.
* libjpeg-turbo Modifications:
* Copyright (C) 2013, Linaro Limited.
- * Copyright (C) 2014-2015, D. R. Commander.
+ * Copyright (C) 2014-2015, 2018, D. R. Commander.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
@@ -304,20 +304,20 @@
rgb = PACK_SHORT_565(r, g, b);
y = GETJSAMPLE(*inptr00++);
- r = range_limit[DITHER_565_R(y + cred, d1)];
- g = range_limit[DITHER_565_G(y + cgreen, d1)];
- b = range_limit[DITHER_565_B(y + cblue, d1)];
- d1 = DITHER_ROTATE(d1);
+ r = range_limit[DITHER_565_R(y + cred, d0)];
+ g = range_limit[DITHER_565_G(y + cgreen, d0)];
+ b = range_limit[DITHER_565_B(y + cblue, d0)];
+ d0 = DITHER_ROTATE(d0);
rgb = PACK_TWO_PIXELS(rgb, PACK_SHORT_565(r, g, b));
WRITE_TWO_PIXELS(outptr0, rgb);
outptr0 += 4;
y = GETJSAMPLE(*inptr01++);
- r = range_limit[DITHER_565_R(y + cred, d0)];
- g = range_limit[DITHER_565_G(y + cgreen, d0)];
- b = range_limit[DITHER_565_B(y + cblue, d0)];
- d0 = DITHER_ROTATE(d0);
+ r = range_limit[DITHER_565_R(y + cred, d1)];
+ g = range_limit[DITHER_565_G(y + cgreen, d1)];
+ b = range_limit[DITHER_565_B(y + cblue, d1)];
+ d1 = DITHER_ROTATE(d1);
rgb = PACK_SHORT_565(r, g, b);
y = GETJSAMPLE(*inptr01++);
