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fix: resolve indexed color image color distortion in PDF output (#1499) #1502

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Merged
asturio merged 1 commit into from
Mar 1, 2026
Merged

fix: resolve indexed color image color distortion in PDF output (#1499) #1502

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142 changes: 142 additions & 0 deletions openpdf-core/src/main/java/org/openpdf/text/Image.java
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Original file line number Diff line number Diff line change
Expand Up @@ -61,12 +61,15 @@
import org.openpdf.text.pdf.PdfObject;
import org.openpdf.text.pdf.PdfReader;
import org.openpdf.text.pdf.PdfStream;
import org.openpdf.text.pdf.PdfString;
import org.openpdf.text.pdf.PdfTemplate;
import org.openpdf.text.pdf.PdfWriter;
import org.openpdf.text.pdf.codec.CCITTG4Encoder;
import java.awt.Graphics2D;
import java.awt.color.ICC_Profile;
import java.awt.image.BufferedImage;
import java.awt.image.IndexColorModel;
import java.awt.image.WritableRaster;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
Expand Down Expand Up @@ -824,6 +827,63 @@ public static Image getInstance(java.awt.Image image, java.awt.Color color,
if (bi.getType() == BufferedImage.TYPE_BYTE_BINARY && bi.getColorModel().getNumColorComponents() <= 2) {
forceBW = true;
}

// Handle indexed color images
if (bi.getColorModel() instanceof IndexColorModel && !forceBW) {
IndexColorModel icm = (IndexColorModel) bi.getColorModel();
int mapSize = icm.getMapSize();
int bitsPerPixel = icm.getPixelSize();

// Ensure bits per pixel is valid (1, 2, 4, or 8)
// For PDF indexed images, bpc should be the bits needed to index the palette
if (bitsPerPixel > 8 || bitsPerPixel == 0) {
bitsPerPixel = 8;
} else if (bitsPerPixel > 4) {
bitsPerPixel = 8;
} else if (bitsPerPixel > 2) {
bitsPerPixel = 4;
} else if (bitsPerPixel > 1) {
bitsPerPixel = 2;
} else {
bitsPerPixel = 1;
}

// Extract palette data
byte[] reds = new byte[mapSize];
byte[] greens = new byte[mapSize];
byte[] blues = new byte[mapSize];
icm.getReds(reds);
icm.getGreens(greens);
icm.getBlues(blues);

// Build palette as RGB byte array
byte[] palette = new byte[mapSize * 3];
for (int i = 0; i < mapSize; i++) {
palette[i * 3] = reds[i];
palette[i * 3 + 1] = greens[i];
palette[i * 3 + 2] = blues[i];
}

// Extract pixel indices
int width = bi.getWidth();
int height = bi.getHeight();
byte[] pixelData = generateIndexedColorPixelData(width, bitsPerPixel, height, bi.getRaster());
// Create indexed image with palette
Image img = Image.getInstance(width, height, 1, bitsPerPixel, pixelData);

// Set up indexed colorspace: [/Indexed /DeviceRGB maxIndex palette]
PdfArray indexed = new PdfArray();
indexed.add(PdfName.INDEXED);
indexed.add(PdfName.DEVICERGB);
indexed.add(new PdfNumber(mapSize - 1));
indexed.add(new PdfString(palette));

PdfDictionary additional = new PdfDictionary();
additional.put(PdfName.COLORSPACE, indexed);
img.setAdditional(additional);

return img;
}
}

java.awt.image.PixelGrabber pg = new java.awt.image.PixelGrabber(image,
Expand Down Expand Up @@ -987,6 +1047,88 @@ public static Image getInstance(java.awt.Image image, java.awt.Color color,
}
}

/**
* Generates PDF-compliant pixel data for indexed color images (IndexColorModel).
* <p>
* This method packs palette indices from a WritableRaster into a byte array that strictly adheres to
* PDF specification requirements for indexed color image storage:
* <ul>
* <li>Pixel indices are packed starting from the Most Significant Bit (MSB, bit 7) of each byte (PDF mandatory rule)</li>
* <li>Each row of pixel data is byte-aligned (padded with zeros to match calculated row stride)</li>
* <li>Supports standard indexed color bit depths: 1, 2, 4, 8 bits per pixel</li>
* <li>Normalizes palette indices to unsigned 0-255 range to prevent invalid negative values</li>
* </ul>
*
* @param width Width of the indexed color image (in pixels)
* @param bitsPerPixel Number of bits per pixel (must be 1, 2, 4, or 8 for valid indexed color)
* @param height Height of the indexed color image (in pixels)
* @param raster WritableRaster containing the indexed color pixel indices (from IndexColorModel BufferedImage)
* @return Byte array of pixel data packed according to PDF indexed color specifications, with row-wise byte alignment
* @see WritableRaster
* @see IndexColorModel
*/
private static byte[] generateIndexedColorPixelData(int width, int bitsPerPixel, int height, WritableRaster raster) {
int rowStride = (width * bitsPerPixel + 7) / 8;
byte[] pixelData = new byte[rowStride * height];

int bytePos = 0;
int bitOffset;

for (int y = 0; y < height; y++) {
bitOffset = 7;
for (int x = 0; x < width; x++) {
int pixelIndex = raster.getSample(x, y, 0);
if (pixelIndex < 0) {
pixelIndex = 0;
}
pixelIndex = pixelIndex & 0xFF;

bitOffset = packPixelByBitDepth(bitsPerPixel, pixelIndex, pixelData, bytePos, bitOffset);

if (bitOffset < 0) {
bytePos++;
bitOffset = 7;
}
}
int usedBytesInRow = bytePos - (y * rowStride);
if (usedBytesInRow < rowStride) {
int padBytes = rowStride - usedBytesInRow;
bytePos += padBytes;
}
}
return pixelData;
}

/**
* Packs a single pixel index into the target byte array based on specified bit depth (PDF MSB-first rule).
*/
private static int packPixelByBitDepth(int bitsPerPixel, int pixelIndex, byte[] pixelData, int bytePos, int bitOffset) {
int currentBitOffset = bitOffset;

switch (bitsPerPixel) {
case 1:
if ((pixelIndex & 0x01) == 1) {
pixelData[bytePos] |= (byte) (1 << currentBitOffset);
}
currentBitOffset--;
break;
case 2:
pixelData[bytePos] |= (byte) ((pixelIndex & 0x03) << (currentBitOffset - 1));
currentBitOffset -= 2;
break;
case 4:
pixelData[bytePos] |= (byte) ((pixelIndex & 0x0F) << (currentBitOffset - 3));
currentBitOffset -= 4;
break;
case 8:
default:
pixelData[bytePos] = (byte) pixelIndex;
currentBitOffset = -1;
break;
}
return currentBitOffset;
}

/**
* Gets an instance of an Image from a java.awt.Image.
*
Expand Down
58 changes: 58 additions & 0 deletions openpdf-core/src/test/java/org/openpdf/text/ImageTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,9 +4,12 @@
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertNull;

import java.awt.image.BufferedImage;
import java.awt.image.IndexColorModel;
import java.io.IOException;
import java.io.InputStream;
import org.junit.jupiter.api.Test;
import org.openpdf.text.pdf.PdfName;

class ImageTest {

Expand Down Expand Up @@ -119,4 +122,59 @@ private byte[] readFileBytes() throws IOException {
return bytes;
}

@Test
void shouldDetectIndexedColorGif() throws Exception {
// Load H.gif which is an indexed color GIF
String fileName = "src/test/resources/H.gif";
Image image = Image.getInstance(fileName);

assertNotNull(image);
// colorspace should be 1 for indexed images (not 3 for RGB)
assertThat(image.getColorspace()).isEqualTo(1);

// Verify that additional colorspace info is set for indexed images
assertThat(image.getAdditional()).isNotNull();
assertThat(image.getAdditional().get(PdfName.COLORSPACE)).isNotNull();
}

@Test
void shouldDetectIndexedColorFromBufferedImage() throws Exception {
// Create an indexed color BufferedImage programmatically
int width = 10;
int height = 10;

// Create a simple 4-color palette (red, green, blue, black)
byte[] reds = {(byte) 255, 0, 0, 0};
byte[] greens = {0, (byte) 255, 0, 0};
byte[] blues = {0, 0, (byte) 255, 0};

IndexColorModel colorModel = new IndexColorModel(
2, // 2 bits per pixel (4 colors)
4, // 4 colors in palette
reds, greens, blues
);

BufferedImage bufferedImage = new BufferedImage(
width, height, BufferedImage.TYPE_BYTE_INDEXED, colorModel
);

// Fill with some pattern
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
bufferedImage.getRaster().setSample(x, y, 0, (x + y) % 4);
}
}

// Convert to Image
Image image = Image.getInstance(bufferedImage, null);

assertNotNull(image);
// Should be indexed (colorspace = 1), not RGB (colorspace = 3)
assertThat(image.getColorspace()).isEqualTo(1);

// Verify that additional colorspace info is set
assertThat(image.getAdditional()).isNotNull();
assertThat(image.getAdditional().get(PdfName.COLORSPACE)).isNotNull();
}

}
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