lib/lowleveljpeg/example_ycbcr444_test.go - external/github.com/google/wuffs - Git at Google

 // Copyright 2025 The Wuffs Authors.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 //
 // SPDX-License-Identifier: Apache-2.0 OR MIT

 package lowleveljpeg_test

 import (
 	"bytes"
 	"fmt"
 	"image/jpeg"
 	"image/png"
 	"log"
 	"os"

 	"github.com/google/wuffs/lib/lowleveljpeg"
 )

 // Example_yCbCr444 demonstrates loading an RGB PNG, converting to YCbCr and to
 // DCT space and saving as a 4:4:4 JPEG. Multiple JPEG outputs from the one PNG
 // input demonstrate making further transforms during conversion.
 func Example_yCbCr444() {
 	// levels holds a rough, ad hoc measure of a coefficient's frequency, in
 	// DCT space. Low (or high) levels[i] mean low (or high) frequency.
 	//
 	// levels[0] == 0 is the DC coefficient. The others are AC coefficients.
 	levels := [64]uint8{
 		0, 1, 2, 3, 4, 5, 6, 7,
 		1, 1, 2, 3, 4, 5, 6, 7,
 		2, 2, 2, 3, 4, 5, 6, 7,
 		3, 3, 3, 3, 4, 5, 6, 7,
 		4, 4, 4, 4, 4, 5, 6, 7,
 		5, 5, 5, 5, 5, 5, 6, 7,
 		6, 6, 6, 6, 6, 6, 6, 7,
 		7, 7, 7, 7, 7, 7, 7, 7,
 	}

 	// Load the source PNG. We will make numerous JPEG encodings of transformed
 	// versions of this PNG image.
 	f, err := os.Open("../../test/data/hippopotamus.regular.png")
 	if err != nil {
 		log.Fatalf("os.Open: %v", err)
 	}
 	defer f.Close()
 	src, err := png.Decode(f)
 	if err != nil {
 		log.Fatalf("png.Decode: %v", err)
 	}

 	// Each example (each output JPEG) has a name fragment and a transform from
 	// source BlockU8 values to destination BlockI16 values.
 	examples := []struct {
 		nameFragment string
 		quality      int
 		transform    func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8)
 	}{{

 		// Apply the ForwardDCT with no further changes. The resultant JPEG is
 		// a low quality (but small in file size) version of the source PNG.
 		nameFragment: "0_quality25",
 		quality:      25,
 		transform: func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8) {
 			dst[0].ForwardDCTFrom(&src[0])
 			dst[1].ForwardDCTFrom(&src[1])
 			dst[2].ForwardDCTFrom(&src[2])
 		},
 	}, {

 		// Ditto, with default quality.
 		nameFragment: "1_quality75",
 		quality:      75,
 		transform: func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8) {
 			dst[0].ForwardDCTFrom(&src[0])
 			dst[1].ForwardDCTFrom(&src[1])
 			dst[2].ForwardDCTFrom(&src[2])
 		},
 	}, {

 		// Ditto, with high quality.
 		nameFragment: "2_quality100",
 		quality:      100,
 		transform: func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8) {
 			dst[0].ForwardDCTFrom(&src[0])
 			dst[1].ForwardDCTFrom(&src[1])
 			dst[2].ForwardDCTFrom(&src[2])
 		},
 	}, {

 		// Like 2_quality100 but swap the Chroma-blue and Chroma-red channels.
 		nameFragment: "3_swap_cb_cr",
 		quality:      100,
 		transform: func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8) {
 			dst[0].ForwardDCTFrom(&src[0])
 			dst[1].ForwardDCTFrom(&src[2]) // Note the "1" and "2".
 			dst[2].ForwardDCTFrom(&src[1]) // Note the "2" and "1".
 		},
 	}, {

 		// Set the 8×8 blocks of the Luma channel to neutral (0x80) except for
 		// each top-left corner, which is black (0x00). Chromas are unchanged.
 		nameFragment: "4_chroma_only",
 		quality:      100,
 		transform: func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8) {
 			s0 := lowleveljpeg.BlockU8{}
 			s0[0] = 0x00
 			for i := 1; i < 64; i++ {
 				s0[i] = lowleveljpeg.BlockU8NeutralValue
 			}
 			dst[0].ForwardDCTFrom(&s0)
 			dst[1].ForwardDCTFrom(&src[1])
 			dst[2].ForwardDCTFrom(&src[2])
 		},
 	}, {

 		// Set the Chroma channels to neutral, as well as any Luma coefficients
 		// that have any horizontal variation (within an 8×8 block). What
 		// remains are the DC and vertical-only Luma coefficients.
 		nameFragment: "5_vertical_luma",
 		quality:      100,
 		transform: func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8) {
 			dst[0].ForwardDCTFrom(&src[0])
 			for i := 0; i < 64; i++ {
 				if (i & 7) != 0 {
 					dst[0][i] = lowleveljpeg.BlockI16NeutralValue
 				}
 			}
 			dst[1] = lowleveljpeg.BlockI16{}
 			dst[2] = lowleveljpeg.BlockI16{}
 		},
 	}, {

 		// Set the Chroma channels to neutral, as well as any medium- or
 		// high-frequency Luma coefficients.
 		nameFragment: "6_low_frequency_luma",
 		quality:      100,
 		transform: func(dst *lowleveljpeg.Array3BlockI16, src *lowleveljpeg.Array3BlockU8) {
 			dst[0] = src[0].ForwardDCT()
 			for i := 0; i < 64; i++ {
 				if levels[i] > 2 {
 					dst[0][i] = 0
 				}
 			}
 			dst[1] = lowleveljpeg.BlockI16{}
 			dst[2] = lowleveljpeg.BlockI16{}
 		},
 	}}

 	// Process each example.
 	for _, example := range examples {
 		// Initialize the encoder.
 		quants := lowleveljpeg.Array2QuantizationFactors{}
 		quants.SetToStandardValues(example.quality)
 		opts := &lowleveljpeg.EncoderOptions{
 			QuantizationFactors: &quants,
 		}
 		bounds := src.Bounds()
 		buf := &bytes.Buffer{}
 		enc := lowleveljpeg.Encoder{}
 		if err := enc.Reset(buf, lowleveljpeg.ColorTypeYCbCr444, bounds.Dx(), bounds.Dy(), opts); err != nil {
 			log.Fatalf("enc.Reset: %v", err)
 		}

 		// Extract, transform and add each MCU (Mininum Coded Unit). For 4:4:4
 		// Chroma subsampling, each MCU is 8×8 and contains 3 blocks: 1 Y, 1
 		// Cb, 1 Cr.
 		srcU8s := lowleveljpeg.Array3BlockU8{}
 		srcI16s := lowleveljpeg.Array3BlockI16{}
 		for y := bounds.Min.Y; y < bounds.Max.Y; y += 8 {
 			for x := bounds.Min.X; x < bounds.Max.X; x += 8 {
 				srcU8s.ExtractYCbCrFrom(src, x, y)
 				example.transform(&srcI16s, &srcU8s)
 				if err := enc.Add3(buf, &srcI16s); err != nil {
 					log.Fatalf("enc.Add3: %v", err)
 				}
 			}
 		}

 		// As a basic consistency check, confirm that the resultant bytes are a
 		// valid JPEG. When copy/pasting this code, you can omit this step.
 		dstBytes := buf.Bytes()
 		if _, err := jpeg.Decode(bytes.NewReader(dstBytes)); err != nil {
 			log.Fatalf("jpeg.Decode: %v", err)
 		}

 		// Change writeTmpFiles to true if you want to visually inspect the output.
 		const writeTmpFiles = false
 		dstFilename := fmt.Sprintf("/tmp/lowleveljpeg_example_%s.jpeg", example.nameFragment)
 		if writeTmpFiles {
 			if err := os.WriteFile(dstFilename, dstBytes, 0644); err != nil {
 				log.Fatalf("os.WriteFile: %v", err)
 			}
 			fmt.Println("Wrote  ", dstFilename)
 		} else {
 			fmt.Println("Skipped", dstFilename)
 		}
 	}

 	// Output:
 	// Skipped /tmp/lowleveljpeg_example_0_quality25.jpeg
 	// Skipped /tmp/lowleveljpeg_example_1_quality75.jpeg
 	// Skipped /tmp/lowleveljpeg_example_2_quality100.jpeg
 	// Skipped /tmp/lowleveljpeg_example_3_swap_cb_cr.jpeg
 	// Skipped /tmp/lowleveljpeg_example_4_chroma_only.jpeg
 	// Skipped /tmp/lowleveljpeg_example_5_vertical_luma.jpeg
 	// Skipped /tmp/lowleveljpeg_example_6_low_frequency_luma.jpeg
 }
	// Copyright 2025 The Wuffs Authors.
	//
	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
	// option. This file may not be copied, modified, or distributed
	// except according to those terms.
	//
	// SPDX-License-Identifier: Apache-2.0 OR MIT

	package lowleveljpeg_test

	import (
	"bytes"
	"fmt"
	"image/jpeg"
	"image/png"
	"log"
	"os"

	"github.com/google/wuffs/lib/lowleveljpeg"
	)

	// Example_yCbCr444 demonstrates loading an RGB PNG, converting to YCbCr and to
	// DCT space and saving as a 4:4:4 JPEG. Multiple JPEG outputs from the one PNG
	// input demonstrate making further transforms during conversion.
	func Example_yCbCr444() {
	// levels holds a rough, ad hoc measure of a coefficient's frequency, in
	// DCT space. Low (or high) levels[i] mean low (or high) frequency.
	//
	// levels[0] == 0 is the DC coefficient. The others are AC coefficients.
	levels := [64]uint8{
	0, 1, 2, 3, 4, 5, 6, 7,
	1, 1, 2, 3, 4, 5, 6, 7,
	2, 2, 2, 3, 4, 5, 6, 7,
	3, 3, 3, 3, 4, 5, 6, 7,
	4, 4, 4, 4, 4, 5, 6, 7,
	5, 5, 5, 5, 5, 5, 6, 7,
	6, 6, 6, 6, 6, 6, 6, 7,
	7, 7, 7, 7, 7, 7, 7, 7,
	}

	// Load the source PNG. We will make numerous JPEG encodings of transformed
	// versions of this PNG image.
	f, err := os.Open("../../test/data/hippopotamus.regular.png")
	if err != nil {
	log.Fatalf("os.Open: %v", err)
	}
	defer f.Close()
	src, err := png.Decode(f)
	if err != nil {
	log.Fatalf("png.Decode: %v", err)
	}

	// Each example (each output JPEG) has a name fragment and a transform from
	// source BlockU8 values to destination BlockI16 values.
	examples := []struct {
	nameFragment string
	quality int
	transform func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8)
	}{{

	// Apply the ForwardDCT with no further changes. The resultant JPEG is
	// a low quality (but small in file size) version of the source PNG.
	nameFragment: "0_quality25",
	quality: 25,
	transform: func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8) {
	dst[0].ForwardDCTFrom(&src[0])
	dst[1].ForwardDCTFrom(&src[1])
	dst[2].ForwardDCTFrom(&src[2])
	},
	}, {

	// Ditto, with default quality.
	nameFragment: "1_quality75",
	quality: 75,
	transform: func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8) {
	dst[0].ForwardDCTFrom(&src[0])
	dst[1].ForwardDCTFrom(&src[1])
	dst[2].ForwardDCTFrom(&src[2])
	},
	}, {

	// Ditto, with high quality.
	nameFragment: "2_quality100",
	quality: 100,
	transform: func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8) {
	dst[0].ForwardDCTFrom(&src[0])
	dst[1].ForwardDCTFrom(&src[1])
	dst[2].ForwardDCTFrom(&src[2])
	},
	}, {

	// Like 2_quality100 but swap the Chroma-blue and Chroma-red channels.
	nameFragment: "3_swap_cb_cr",
	quality: 100,
	transform: func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8) {
	dst[0].ForwardDCTFrom(&src[0])
	dst[1].ForwardDCTFrom(&src[2]) // Note the "1" and "2".
	dst[2].ForwardDCTFrom(&src[1]) // Note the "2" and "1".
	},
	}, {

	// Set the 8×8 blocks of the Luma channel to neutral (0x80) except for
	// each top-left corner, which is black (0x00). Chromas are unchanged.
	nameFragment: "4_chroma_only",
	quality: 100,
	transform: func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8) {
	s0 := lowleveljpeg.BlockU8{}
	s0[0] = 0x00
	for i := 1; i < 64; i++ {
	s0[i] = lowleveljpeg.BlockU8NeutralValue
	}
	dst[0].ForwardDCTFrom(&s0)
	dst[1].ForwardDCTFrom(&src[1])
	dst[2].ForwardDCTFrom(&src[2])
	},
	}, {

	// Set the Chroma channels to neutral, as well as any Luma coefficients
	// that have any horizontal variation (within an 8×8 block). What
	// remains are the DC and vertical-only Luma coefficients.
	nameFragment: "5_vertical_luma",
	quality: 100,
	transform: func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8) {
	dst[0].ForwardDCTFrom(&src[0])
	for i := 0; i < 64; i++ {
	if (i & 7) != 0 {
	dst[0][i] = lowleveljpeg.BlockI16NeutralValue
	}
	}
	dst[1] = lowleveljpeg.BlockI16{}
	dst[2] = lowleveljpeg.BlockI16{}
	},
	}, {

	// Set the Chroma channels to neutral, as well as any medium- or
	// high-frequency Luma coefficients.
	nameFragment: "6_low_frequency_luma",
	quality: 100,
	transform: func(dst lowleveljpeg.Array3BlockI16, src lowleveljpeg.Array3BlockU8) {
	dst[0] = src[0].ForwardDCT()
	for i := 0; i < 64; i++ {
	if levels[i] > 2 {
	dst[0][i] = 0
	}
	}
	dst[1] = lowleveljpeg.BlockI16{}
	dst[2] = lowleveljpeg.BlockI16{}
	},
	}}

	// Process each example.
	for _, example := range examples {
	// Initialize the encoder.
	quants := lowleveljpeg.Array2QuantizationFactors{}
	quants.SetToStandardValues(example.quality)
	opts := &lowleveljpeg.EncoderOptions{
	QuantizationFactors: &quants,
	}
	bounds := src.Bounds()
	buf := &bytes.Buffer{}
	enc := lowleveljpeg.Encoder{}
	if err := enc.Reset(buf, lowleveljpeg.ColorTypeYCbCr444, bounds.Dx(), bounds.Dy(), opts); err != nil {
	log.Fatalf("enc.Reset: %v", err)
	}

	// Extract, transform and add each MCU (Mininum Coded Unit). For 4:4:4
	// Chroma subsampling, each MCU is 8×8 and contains 3 blocks: 1 Y, 1
	// Cb, 1 Cr.
	srcU8s := lowleveljpeg.Array3BlockU8{}
	srcI16s := lowleveljpeg.Array3BlockI16{}
	for y := bounds.Min.Y; y < bounds.Max.Y; y += 8 {
	for x := bounds.Min.X; x < bounds.Max.X; x += 8 {
	srcU8s.ExtractYCbCrFrom(src, x, y)
	example.transform(&srcI16s, &srcU8s)
	if err := enc.Add3(buf, &srcI16s); err != nil {
	log.Fatalf("enc.Add3: %v", err)
	}
	}
	}

	// As a basic consistency check, confirm that the resultant bytes are a
	// valid JPEG. When copy/pasting this code, you can omit this step.
	dstBytes := buf.Bytes()
	if _, err := jpeg.Decode(bytes.NewReader(dstBytes)); err != nil {
	log.Fatalf("jpeg.Decode: %v", err)
	}

	// Change writeTmpFiles to true if you want to visually inspect the output.
	const writeTmpFiles = false
	dstFilename := fmt.Sprintf("/tmp/lowleveljpeg_example_%s.jpeg", example.nameFragment)
	if writeTmpFiles {
	if err := os.WriteFile(dstFilename, dstBytes, 0644); err != nil {
	log.Fatalf("os.WriteFile: %v", err)
	}
	fmt.Println("Wrote ", dstFilename)
	} else {
	fmt.Println("Skipped", dstFilename)
	}
	}

	// Output:
	// Skipped /tmp/lowleveljpeg_example_0_quality25.jpeg
	// Skipped /tmp/lowleveljpeg_example_1_quality75.jpeg
	// Skipped /tmp/lowleveljpeg_example_2_quality100.jpeg
	// Skipped /tmp/lowleveljpeg_example_3_swap_cb_cr.jpeg
	// Skipped /tmp/lowleveljpeg_example_4_chroma_only.jpeg
	// Skipped /tmp/lowleveljpeg_example_5_vertical_luma.jpeg
	// Skipped /tmp/lowleveljpeg_example_6_low_frequency_luma.jpeg
	}