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oboasturio
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asturio
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fix: resolve indexed color image color distortion in PDF output (#1499)
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‎openpdf-core/src/main/java/org/openpdf/text/Image.java‎

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Original file line numberDiff line numberDiff line change
@@ -61,12 +61,15 @@
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import org.openpdf.text.pdf.PdfObject;
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import org.openpdf.text.pdf.PdfReader;
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import org.openpdf.text.pdf.PdfStream;
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import org.openpdf.text.pdf.PdfString;
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import org.openpdf.text.pdf.PdfTemplate;
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import org.openpdf.text.pdf.PdfWriter;
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import org.openpdf.text.pdf.codec.CCITTG4Encoder;
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import java.awt.Graphics2D;
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import java.awt.color.ICC_Profile;
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import java.awt.image.BufferedImage;
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import java.awt.image.IndexColorModel;
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import java.awt.image.WritableRaster;
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import java.io.IOException;
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import java.io.InputStream;
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import java.lang.reflect.Constructor;
@@ -824,6 +827,63 @@ public static Image getInstance(java.awt.Image image, java.awt.Color color,
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if (bi.getType() == BufferedImage.TYPE_BYTE_BINARY && bi.getColorModel().getNumColorComponents() <= 2) {
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forceBW = true;
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}
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// Handle indexed color images
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if (bi.getColorModel() instanceof IndexColorModel && !forceBW) {
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IndexColorModel icm = (IndexColorModel) bi.getColorModel();
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int mapSize = icm.getMapSize();
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int bitsPerPixel = icm.getPixelSize();
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// Ensure bits per pixel is valid (1, 2, 4, or 8)
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// For PDF indexed images, bpc should be the bits needed to index the palette
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if (bitsPerPixel > 8 || bitsPerPixel == 0) {
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bitsPerPixel = 8;
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} else if (bitsPerPixel > 4) {
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bitsPerPixel = 8;
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} else if (bitsPerPixel > 2) {
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bitsPerPixel = 4;
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} else if (bitsPerPixel > 1) {
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bitsPerPixel = 2;
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} else {
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bitsPerPixel = 1;
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}
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// Extract palette data
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byte[] reds = new byte[mapSize];
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byte[] greens = new byte[mapSize];
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byte[] blues = new byte[mapSize];
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icm.getReds(reds);
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icm.getGreens(greens);
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icm.getBlues(blues);
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// Build palette as RGB byte array
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byte[] palette = new byte[mapSize * 3];
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for (int i = 0; i < mapSize; i++) {
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palette[i * 3] = reds[i];
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palette[i * 3 + 1] = greens[i];
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palette[i * 3 + 2] = blues[i];
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}
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// Extract pixel indices
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int width = bi.getWidth();
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int height = bi.getHeight();
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byte[] pixelData = generateIndexedColorPixelData(width, bitsPerPixel, height, bi.getRaster());
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// Create indexed image with palette
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Image img = Image.getInstance(width, height, 1, bitsPerPixel, pixelData);
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// Set up indexed colorspace: [/Indexed /DeviceRGB maxIndex palette]
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PdfArray indexed = new PdfArray();
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indexed.add(PdfName.INDEXED);
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indexed.add(PdfName.DEVICERGB);
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indexed.add(new PdfNumber(mapSize - 1));
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indexed.add(new PdfString(palette));
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PdfDictionary additional = new PdfDictionary();
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additional.put(PdfName.COLORSPACE, indexed);
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img.setAdditional(additional);
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return img;
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}
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}
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java.awt.image.PixelGrabber pg = new java.awt.image.PixelGrabber(image,
@@ -987,6 +1047,88 @@ public static Image getInstance(java.awt.Image image, java.awt.Color color,
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}
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}
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/**
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* Generates PDF-compliant pixel data for indexed color images (IndexColorModel).
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* <p>
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* This method packs palette indices from a WritableRaster into a byte array that strictly adheres to
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* PDF specification requirements for indexed color image storage:
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* <ul>
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* <li>Pixel indices are packed starting from the Most Significant Bit (MSB, bit 7) of each byte (PDF mandatory rule)</li>
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* <li>Each row of pixel data is byte-aligned (padded with zeros to match calculated row stride)</li>
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* <li>Supports standard indexed color bit depths: 1, 2, 4, 8 bits per pixel</li>
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* <li>Normalizes palette indices to unsigned 0-255 range to prevent invalid negative values</li>
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* </ul>
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*
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* @param width Width of the indexed color image (in pixels)
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* @param bitsPerPixel Number of bits per pixel (must be 1, 2, 4, or 8 for valid indexed color)
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* @param height Height of the indexed color image (in pixels)
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* @param raster WritableRaster containing the indexed color pixel indices (from IndexColorModel BufferedImage)
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* @return Byte array of pixel data packed according to PDF indexed color specifications, with row-wise byte alignment
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* @see WritableRaster
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* @see IndexColorModel
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*/
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private static byte[] generateIndexedColorPixelData(int width, int bitsPerPixel, int height, WritableRaster raster) {
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int rowStride = (width * bitsPerPixel + 7) / 8;
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byte[] pixelData = new byte[rowStride * height];
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int bytePos = 0;
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int bitOffset;
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for (int y = 0; y < height; y++) {
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bitOffset = 7;
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for (int x = 0; x < width; x++) {
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int pixelIndex = raster.getSample(x, y, 0);
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if (pixelIndex < 0) {
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pixelIndex = 0;
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}
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pixelIndex = pixelIndex & 0xFF;
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bitOffset = packPixelByBitDepth(bitsPerPixel, pixelIndex, pixelData, bytePos, bitOffset);
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if (bitOffset < 0) {
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bytePos++;
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bitOffset = 7;
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}
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}
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int usedBytesInRow = bytePos - (y * rowStride);
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if (usedBytesInRow < rowStride) {
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int padBytes = rowStride - usedBytesInRow;
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bytePos += padBytes;
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}
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}
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return pixelData;
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}
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/**
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* Packs a single pixel index into the target byte array based on specified bit depth (PDF MSB-first rule).
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*/
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private static int packPixelByBitDepth(int bitsPerPixel, int pixelIndex, byte[] pixelData, int bytePos, int bitOffset) {
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int currentBitOffset = bitOffset;
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switch (bitsPerPixel) {
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case 1:
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if ((pixelIndex & 0x01) == 1) {
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pixelData[bytePos] |= (byte) (1 << currentBitOffset);
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}
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currentBitOffset--;
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break;
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case 2:
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pixelData[bytePos] |= (byte) ((pixelIndex & 0x03) << (currentBitOffset - 1));
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currentBitOffset -= 2;
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break;
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case 4:
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pixelData[bytePos] |= (byte) ((pixelIndex & 0x0F) << (currentBitOffset - 3));
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currentBitOffset -= 4;
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break;
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case 8:
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default:
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pixelData[bytePos] = (byte) pixelIndex;
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currentBitOffset = -1;
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break;
1128+
}
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return currentBitOffset;
1130+
}
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/**
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* Gets an instance of an Image from a java.awt.Image.
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*

‎openpdf-core/src/test/java/org/openpdf/text/ImageTest.java‎

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@@ -4,9 +4,12 @@
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import static org.junit.jupiter.api.Assertions.assertNotNull;
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import static org.junit.jupiter.api.Assertions.assertNull;
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import java.awt.image.BufferedImage;
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import java.awt.image.IndexColorModel;
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import java.io.IOException;
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import java.io.InputStream;
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import org.junit.jupiter.api.Test;
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import org.openpdf.text.pdf.PdfName;
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class ImageTest {
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@@ -119,4 +122,59 @@ private byte[] readFileBytes() throws IOException {
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return bytes;
120123
}
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@Test
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void shouldDetectIndexedColorGif() throws Exception {
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// Load H.gif which is an indexed color GIF
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String fileName = "src/test/resources/H.gif";
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Image image = Image.getInstance(fileName);
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assertNotNull(image);
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// colorspace should be 1 for indexed images (not 3 for RGB)
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assertThat(image.getColorspace()).isEqualTo(1);
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// Verify that additional colorspace info is set for indexed images
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assertThat(image.getAdditional()).isNotNull();
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assertThat(image.getAdditional().get(PdfName.COLORSPACE)).isNotNull();
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}
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@Test
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void shouldDetectIndexedColorFromBufferedImage() throws Exception {
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// Create an indexed color BufferedImage programmatically
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int width = 10;
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int height = 10;
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// Create a simple 4-color palette (red, green, blue, black)
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byte[] reds = {(byte) 255, 0, 0, 0};
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byte[] greens = {0, (byte) 255, 0, 0};
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byte[] blues = {0, 0, (byte) 255, 0};
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IndexColorModel colorModel = new IndexColorModel(
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2, // 2 bits per pixel (4 colors)
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4, // 4 colors in palette
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reds, greens, blues
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);
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BufferedImage bufferedImage = new BufferedImage(
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width, height, BufferedImage.TYPE_BYTE_INDEXED, colorModel
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);
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// Fill with some pattern
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for (int y = 0; y < height; y++) {
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for (int x = 0; x < width; x++) {
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bufferedImage.getRaster().setSample(x, y, 0, (x + y) % 4);
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}
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}
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// Convert to Image
169+
Image image = Image.getInstance(bufferedImage, null);
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assertNotNull(image);
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// Should be indexed (colorspace = 1), not RGB (colorspace = 3)
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assertThat(image.getColorspace()).isEqualTo(1);
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// Verify that additional colorspace info is set
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assertThat(image.getAdditional()).isNotNull();
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assertThat(image.getAdditional().get(PdfName.COLORSPACE)).isNotNull();
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}
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}

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