YCbCrConverter.java
/*
* Copyright (c) 2015, Harald Kuhr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
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* * Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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package com.twelvemonkeys.imageio.color;
/**
* Fast YCbCr to RGB conversion.
*
* @author <a href="mailto:harald.kuhr@gmail.com">Harald Kuhr</a>
* @author Original code by Werner Randelshofer (used by permission).
*/
public final class YCbCrConverter {
/**
* Define tables for YCC->RGB color space conversion.
*/
private final static int SCALEBITS = 16;
private final static int MAXJSAMPLE = 255;
private final static int CENTERJSAMPLE = 128;
private final static int ONE_HALF = 1 << (SCALEBITS - 1);
private final static class JPEG {
private final static int[] Cr_R_LUT = new int[MAXJSAMPLE + 1];
private final static int[] Cb_B_LUT = new int[MAXJSAMPLE + 1];
private final static int[] Cr_G_LUT = new int[MAXJSAMPLE + 1];
private final static int[] Cb_G_LUT = new int[MAXJSAMPLE + 1];
/**
* Initializes tables for YCC->RGB color space conversion.
*/
private static void buildYCCtoRGBtable() {
if (ColorSpaces.DEBUG) {
System.err.println("Building JPEG YCbCr conversion table");
}
for (int i = 0, x = -CENTERJSAMPLE; i <= MAXJSAMPLE; i++, x++) {
// i is the actual input pixel value, in the range 0..MAXJSAMPLE
// The Cb or Cr value we are thinking of is x = i - CENTERJSAMPLE
// Cr=>R value is nearest int to 1.40200 * x
Cr_R_LUT[i] = (int) ((1.40200 * (1 << SCALEBITS) + 0.5) * x + ONE_HALF) >> SCALEBITS;
// Cb=>B value is nearest int to 1.77200 * x
Cb_B_LUT[i] = (int) ((1.77200 * (1 << SCALEBITS) + 0.5) * x + ONE_HALF) >> SCALEBITS;
// Cr=>G value is scaled-up -0.71414 * x
Cr_G_LUT[i] = -(int) (0.71414 * (1 << SCALEBITS) + 0.5) * x;
// Cb=>G value is scaled-up -0.34414 * x
// We also add in ONE_HALF so that need not do it in inner loop
Cb_G_LUT[i] = -(int) ((0.34414) * (1 << SCALEBITS) + 0.5) * x + ONE_HALF;
}
}
static {
buildYCCtoRGBtable();
}
}
private final static class ITU_R_601 {
private final static int[] Cr_R_LUT = new int[MAXJSAMPLE + 1];
private final static int[] Cb_B_LUT = new int[MAXJSAMPLE + 1];
private final static int[] Cr_G_LUT = new int[MAXJSAMPLE + 1];
private final static int[] Cb_G_LUT = new int[MAXJSAMPLE + 1];
private final static int[] Y_LUT = new int[MAXJSAMPLE + 1];
/**
* Initializes tables for YCC->RGB color space conversion.
*/
private static void buildYCCtoRGBtable() {
if (ColorSpaces.DEBUG) {
System.err.println("Building ITU-R REC.601 YCbCr conversion table");
}
for (int i = 0, x = -CENTERJSAMPLE; i <= MAXJSAMPLE; i++, x++) {
// i is the actual input pixel value, in the range 0..MAXJSAMPLE
// The Cb or Cr value we are thinking of is x = i - CENTERJSAMPLE
// Y'CbCr to RGB conversion, using values from BT.601 specification:
// R = 1.16438 * (Y'-16) + 1.59603 * (Cr-128)
// G = 1.16438 * (Y'-16) - 0.39176 * (Cb-128) - 0.81297 * (Cr-128)
// B = 1.16438 * (Y'-16) + 2.01723 * (Cb-128)
// Cr=>R value is nearest int to 1.59603 * x
Cr_R_LUT[i] = ((int) (1.59603 * (1 << SCALEBITS) + 0.5) * x + ONE_HALF) >> SCALEBITS;
// Cb=>B value is nearest int to 2.01723 * x
Cb_B_LUT[i] = ((int) (2.01723 * (1 << SCALEBITS) + 0.5) * x + ONE_HALF) >> SCALEBITS;
// Cr=>G value is scaled-up -0.81297 * x
Cr_G_LUT[i] = -(int) (0.81297 * (1 << SCALEBITS) + 0.5) * x;
// Cb=>G value is scaled-up -0.39176 * x
// We also add in ONE_HALF so that need not do it in inner loop
Cb_G_LUT[i] = -(int) ((0.39176) * (1 << SCALEBITS) + 0.5) * x + ONE_HALF;
// Y`=>RGB
Y_LUT[i] = ((int) (1.16438 * (1 << SCALEBITS) + 0.5) * (i - 16) + ONE_HALF) >> SCALEBITS;
}
}
static {
buildYCCtoRGBtable();
}
}
public static void convertYCbCr2RGB(final byte[] yCbCr, final byte[] rgb, final double[] coefficients, double[] referenceBW, final int offset) {
double y;
double cb;
double cr;
if (referenceBW == null) {
// Default case
y = (yCbCr[offset] & 0xff);
cb = (yCbCr[offset + 1] & 0xff) - 128;
cr = (yCbCr[offset + 2] & 0xff) - 128;
}
else {
// Custom values
y = ((yCbCr[offset] & 0xff) - referenceBW[0]) * 255.0 / (referenceBW[1] - referenceBW[0]);
cb = ((yCbCr[offset + 1] & 0xff) - referenceBW[2]) * 127.0 / (referenceBW[3] - referenceBW[2]);
cr = ((yCbCr[offset + 2] & 0xff) - referenceBW[4]) * 127.0 / (referenceBW[5] - referenceBW[4]);
}
double lumaRed = coefficients[0];
double lumaGreen = coefficients[1];
double lumaBlue = coefficients[2];
int red = (int) Math.round(cr * (2.0 - 2.0 * lumaRed) + y);
int blue = (int) Math.round(cb * (2.0 - 2.0 * lumaBlue) + y);
int green = (int) Math.round((y - lumaRed * red - lumaBlue * blue) / lumaGreen);
rgb[offset] = clamp(red);
rgb[offset + 2] = clamp(blue);
rgb[offset + 1] = clamp(green);
}
public static void convertJPEGYCbCr2RGB(final byte[] yCbCr, final byte[] rgb, final int offset) {
int y = yCbCr[offset ] & 0xff;
int cb = yCbCr[offset + 1] & 0xff;
int cr = yCbCr[offset + 2] & 0xff;
rgb[offset ] = clamp(y + JPEG.Cr_R_LUT[cr]);
rgb[offset + 1] = clamp(y + (JPEG.Cb_G_LUT[cb] + JPEG.Cr_G_LUT[cr] >> SCALEBITS));
rgb[offset + 2] = clamp(y + JPEG.Cb_B_LUT[cb]);
}
public static void convertRec601YCbCr2RGB(final byte[] yCbCr, final byte[] rgb, final int offset) {
int y = yCbCr[offset ] & 0xff;
int cb = yCbCr[offset + 1] & 0xff;
int cr = yCbCr[offset + 2] & 0xff;
rgb[offset ] = clamp(ITU_R_601.Y_LUT[y] + ITU_R_601.Cr_R_LUT[cr]);
rgb[offset + 1] = clamp(ITU_R_601.Y_LUT[y] + (ITU_R_601.Cr_G_LUT[cr] + ITU_R_601.Cb_G_LUT[cb] >> SCALEBITS));
rgb[offset + 2] = clamp(ITU_R_601.Y_LUT[y] + ITU_R_601.Cb_B_LUT[cb]);
}
private static byte clamp(final int val) {
return (byte) Math.max(0, Math.min(255, val));
}
}