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Implement decoding of compressed alpha chunks, alpha filtering

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This commit is contained in:
Simon Kammermeier 2022-08-30 15:41:53 +02:00
parent 6608f61353
commit 67b48ce1e3
2 changed files with 110 additions and 29 deletions
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8
imageio/imageio-webp/src/main/java/com/twelvemonkeys/imageio/plugins/webp/AlphaFiltering.java Normal file
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@ -0,0 +1,8 @@
package com.twelvemonkeys.imageio.plugins.webp;
public interface AlphaFiltering {
int NONE = 0;
int HORIZONTAL = 1;
int VERTICAL = 2;
int GRADIENT = 3;
}

131
imageio/imageio-webp/src/main/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReader.java
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@ -38,6 +38,7 @@ import java.awt.image.BufferedImage;
import java.awt.image.ColorConvertOp; import java.awt.image.ColorConvertOp;
import java.awt.image.ColorModel; import java.awt.image.ColorModel;
import java.awt.image.DataBuffer; import java.awt.image.DataBuffer;
import java.awt.image.Raster;
import java.awt.image.WritableRaster; import java.awt.image.WritableRaster;
import java.io.IOException; import java.io.IOException;
import java.nio.ByteOrder; import java.nio.ByteOrder;
@ -465,35 +466,7 @@ final class WebPImageReader extends ImageReaderBase {
switch (nextChunk) { switch (nextChunk) {
case WebP.CHUNK_ALPH: case WebP.CHUNK_ALPH:
int reserved = (int) imageInput.readBits(2); readAlpha(destination, param);
if (reserved != 0) {
// Spec says SHOULD be 0
processWarningOccurred(String.format("Unexpected 'ALPH' chunk reserved value, expected 0: %d", reserved));
}
int preProcessing = (int) imageInput.readBits(2);
int filtering = (int) imageInput.readBits(2);
int compression = (int) imageInput.readBits(2);
if (DEBUG) {
System.out.println("preProcessing: " + preProcessing);
System.out.println("filtering: " + filtering);
System.out.println("compression: " + compression);
}
switch (compression) {
case 0:
readUncompressedAlpha(destination.getAlphaRaster());
break;
case 1:
opaqueAlpha(destination.getAlphaRaster()); // TODO: Remove when correctly implemented!
// readVP8Lossless(destination.getAlphaRaster(), param);
break;
default:
processWarningOccurred("Unknown WebP alpha compression: " + compression);
opaqueAlpha(destination.getAlphaRaster());
break;
}
break; break;
@ -527,6 +500,106 @@ final class WebPImageReader extends ImageReaderBase {
} }
} }
private void readAlpha(BufferedImage destination, ImageReadParam param) throws IOException {
int reserved = (int) imageInput.readBits(2);
if (reserved != 0) {
// Spec says SHOULD be 0
processWarningOccurred(
String.format("Unexpected 'ALPH' chunk reserved value, expected 0: %d", reserved));
}
int preProcessing = (int) imageInput.readBits(2);
int filtering = (int) imageInput.readBits(2);
int compression = (int) imageInput.readBits(2);
if (DEBUG) {
System.out.println("preProcessing: " + preProcessing);
System.out.println("filtering: " + filtering);
System.out.println("compression: " + compression);
}
WritableRaster alphaRaster = destination.getAlphaRaster();
switch (compression) {
case 0:
readUncompressedAlpha(alphaRaster);
break;
case 1:
WritableRaster tempRaster = Raster.createInterleavedRaster(DataBuffer.TYPE_BYTE,
destination.getWidth(), destination.getHeight(), 4, null);
//Simulate header
imageInput.seek(imageInput.getStreamPosition() - 5);
readVP8Lossless(tempRaster, param);
//Copy from green (band 1) in temp to alpha in destination
alphaRaster.setRect(tempRaster.createChild(0, 0, tempRaster.getWidth(),
tempRaster.getHeight(), 0, 0, new int[] {1}));
break;
default:
processWarningOccurred("Unknown WebP alpha compression: " + compression);
opaqueAlpha(alphaRaster);
break;
}
if (filtering != AlphaFiltering.NONE) {
for (int y = 0; y < destination.getHeight(); y++) {
for (int x = 0; x < destination.getWidth(); x++) {
int predictorAlpha = getPredictorAlpha(alphaRaster, filtering, y, x);
alphaRaster.setSample(x, y, 0, alphaRaster.getSample(x, y, 0) + predictorAlpha % 256);
}
}
}
}
private int getPredictorAlpha(WritableRaster alphaRaster, int filtering, int y, int x) {
switch (filtering) {
case AlphaFiltering.NONE:
return 0;
case AlphaFiltering.HORIZONTAL:
if (x == 0) {
if (y == 0) {
return 0;
}
else {
return alphaRaster.getSample(0, y - 1, 0);
}
}
else {
return alphaRaster.getSample(x - 1, y, 0);
}
case AlphaFiltering.VERTICAL:
if (y == 0) {
if (x == 0) {
return 0;
}
else {
return alphaRaster.getSample(x - 1, 0, 0);
}
}
else {
return alphaRaster.getSample(x, y - 1, 0);
}
case AlphaFiltering.GRADIENT:
if (x == 0 && y == 0) {
return 0;
}
else if (x == 0) {
return alphaRaster.getSample(0, y - 1, 0);
}
else if (y == 0) {
return alphaRaster.getSample(x - 1, 0, 0);
}
else {
int left = alphaRaster.getSample(x - 1, y, 0);
int top = alphaRaster.getSample(x, y - 1, 0);
int topLeft = alphaRaster.getSample(x - 1, y - 1, 0);
return Math.max(0, Math.min(left + top - topLeft, 255));
}
default:
processWarningOccurred("Unknown WebP alpha filtering: " + filtering);
return 0;
}
}
private void applyICCProfileIfNeeded(final BufferedImage destination) { private void applyICCProfileIfNeeded(final BufferedImage destination) {
if (iccProfile != null) { if (iccProfile != null) {
ColorModel colorModel = destination.getColorModel(); ColorModel colorModel = destination.getColorModel();