http://xmlgraphics.apache.org/commons/: Apache XML Graphics Commons is a library that consists of several reusable components used by Apache Batik and Apache FOP. Many of these components can easily be used separately outside the domains of SVG and XSL-FO. (Apache Software Foundation) 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* $Id: PNGImageDecoder.java 1732018 2016-02-24 04:51:06Z gadams $ */

package org.apache.xmlgraphics.image.codec.png;

import java.awt.Color;
import java.awt.Point;
import java.awt.Transparency;
import java.awt.color.ColorSpace;
import java.awt.image.ColorModel;
import java.awt.image.ComponentColorModel;
import java.awt.image.DataBuffer;
import java.awt.image.DataBufferByte;
import java.awt.image.DataBufferUShort;
import java.awt.image.IndexColorModel;
import java.awt.image.Raster;
import java.awt.image.RenderedImage;
import java.awt.image.SampleModel;
import java.awt.image.WritableRaster;
import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.SequenceInputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.List;
import java.util.Locale;
import java.util.TimeZone;
import java.util.zip.Inflater;
import java.util.zip.InflaterInputStream;

import javax.imageio.stream.ImageInputStream;

import org.apache.xmlgraphics.image.codec.util.ImageDecoderImpl;
import org.apache.xmlgraphics.image.codec.util.ImageInputStreamSeekableStreamAdapter;
import org.apache.xmlgraphics.image.codec.util.PropertyUtil;
import org.apache.xmlgraphics.image.codec.util.SeekableStream;
import org.apache.xmlgraphics.image.codec.util.SimpleRenderedImage;
import org.apache.xmlgraphics.image.loader.ImageSize;
import org.apache.xmlgraphics.image.loader.impl.PNGConstants;

// CSOFF: ConstantName
// CSOFF: InnerAssignment
// CSOFF: MethodName
// CSOFF: MissingSwitchDefault
// CSOFF: MultipleVariableDeclarations
// CSOFF: NoWhitespaceAfter
// CSOFF: OperatorWrap
// CSOFF: WhitespaceAround


Version:$Id: PNGImageDecoder.java 1732018 2016-02-24 04:51:06Z gadams $
/**
 * @version $Id: PNGImageDecoder.java 1732018 2016-02-24 04:51:06Z gadams $
 */
public class PNGImageDecoder extends ImageDecoderImpl {

    public PNGImageDecoder(InputStream input,
                           PNGDecodeParam param) {
        super(input, param);
    }

    @Override
    public RenderedImage decodeAsRenderedImage(int page) throws IOException {
        if (page != 0) {
            throw new IOException(PropertyUtil.getString("PNGImageDecoder19"));
        }
        return new PNGImage(input, (PNGDecodeParam)param);
    }

    public static void readPNGHeader(ImageInputStream inputStream, ImageSize size) throws IOException {
        SeekableStream seekStream = new ImageInputStreamSeekableStreamAdapter(inputStream) {
            public void close() throws IOException {
            }
        };
        PNGImage pngImage = new PNGImage(seekStream);
        size.setSizeInPixels(pngImage.getWidth(), pngImage.getHeight());
        double dpiHorz = size.getDpiHorizontal();
        double dpiVert = size.getDpiVertical();
        if (pngImage.unitSpecifier == 1) {
            if (pngImage.xPixelsPerUnit != 0) {
                dpiHorz = pngImage.xPixelsPerUnit * 0.0254;
            }
            if (pngImage.yPixelsPerUnit != 0) {
                dpiVert = pngImage.yPixelsPerUnit * 0.0254;
            }
        }
        size.setResolution(dpiHorz, dpiVert);
        size.calcSizeFromPixels();
    }
}


TO DO:
zTXt chunks

/**
 * TO DO:
 *
 * zTXt chunks
 *
 */
class PNGImage extends SimpleRenderedImage implements PNGConstants {

    private static final String[] colorTypeNames = {
        "Grayscale", "Error", "Truecolor", "Index",
        "Grayscale with alpha", "Error", "Truecolor with alpha"
    };

    private int[][] bandOffsets = {
        null,
        { 0 }, // G
        { 0, 1 }, // GA in GA order
        { 0, 1, 2 }, // RGB in RGB order
        { 0, 1, 2, 3 } // RGBA in RGBA order
    };

    private int bitDepth;
    private int colorType;

    private int compressionMethod;
    private int filterMethod;
    private int interlaceMethod;

    private int paletteEntries;
    private byte[] redPalette;
    private byte[] greenPalette;
    private byte[] bluePalette;
    private byte[] alphaPalette;

    private int bkgdRed;
    private int bkgdGreen;
    private int bkgdBlue;

    private int grayTransparentAlpha;
    private int redTransparentAlpha;
    private int greenTransparentAlpha;
    private int blueTransparentAlpha;

    private int maxOpacity;

    private int[] significantBits;

    // Parameter information

    // If true, the user wants destination alpha where applicable.
    private boolean suppressAlpha;

    // If true, perform palette lookup internally
    private boolean expandPalette;

    // If true, output < 8 bit gray images in 8 bit components format
    private boolean output8BitGray;

    // Create an alpha channel in the destination color model.
    private boolean outputHasAlphaPalette;

    // Perform gamma correction on the image
    private boolean performGammaCorrection;

    // Expand GA to GGGA for compatbility with Java2D
    private boolean expandGrayAlpha;

    // Produce an instance of PNGEncodeParam
    private boolean generateEncodeParam;

    // PNGDecodeParam controlling decode process
    private PNGDecodeParam decodeParam;

    // PNGEncodeParam to store file details in
    private PNGEncodeParam encodeParam;

    private boolean emitProperties = true;

    private float fileGamma = 45455 / 100000.0F;

    private float userExponent = 1.0F;

    private float displayExponent = 2.2F;

    private float[] chromaticity;

    private int sRGBRenderingIntent = -1;

    // Post-processing step implied by above parameters
    private int postProcess = POST_NONE;

    protected int xPixelsPerUnit;
    protected int yPixelsPerUnit;
    protected int unitSpecifier;

    // Possible post-processing steps

    // Do nothing
    private static final int POST_NONE = 0;

    // Gamma correct only
    private static final int POST_GAMMA = 1;

    // Push gray values through grayLut to expand to 8 bits
    private static final int POST_GRAY_LUT = 2;

    // Push gray values through grayLut to expand to 8 bits, add alpha
    private static final int POST_GRAY_LUT_ADD_TRANS = 3;

    // Push palette value through R,G,B lookup tables
    private static final int POST_PALETTE_TO_RGB = 4;

    // Push palette value through R,G,B,A lookup tables
    private static final int POST_PALETTE_TO_RGBA = 5;

    // Add transparency to a given gray value (w/ optional gamma)
    private static final int POST_ADD_GRAY_TRANS = 6;

    // Add transparency to a given RGB value (w/ optional gamma)
    private static final int POST_ADD_RGB_TRANS = 7;

    // Remove the alpha channel from a gray image (w/ optional gamma)
    private static final int POST_REMOVE_GRAY_TRANS = 8;

    // Remove the alpha channel from an RGB image (w/optional gamma)
    private static final int POST_REMOVE_RGB_TRANS = 9;

    // Mask to add expansion of GA -> GGGA
    private static final int POST_EXP_MASK = 16;

    // Expand gray to G/G/G
    private static final int POST_GRAY_ALPHA_EXP =
        POST_NONE | POST_EXP_MASK;

    // Expand gray to G/G/G through a gamma lut
    private static final int POST_GAMMA_EXP =
        POST_GAMMA | POST_EXP_MASK;

    // Push gray values through grayLut to expand to 8 bits, expand, add alpha
    private static final int POST_GRAY_LUT_ADD_TRANS_EXP =
        POST_GRAY_LUT_ADD_TRANS | POST_EXP_MASK;

    // Add transparency to a given gray value, expand
    private static final int POST_ADD_GRAY_TRANS_EXP =
        POST_ADD_GRAY_TRANS | POST_EXP_MASK;

    private List<InputStream> streamVec = new ArrayList<InputStream>();
    private DataInputStream dataStream;

    private int bytesPerPixel; // number of bytes per input pixel
    private int inputBands;
    private int outputBands;

    // Number of private chunks
    private int chunkIndex;

    private List textKeys = new ArrayList();
    private List textStrings = new ArrayList();

    private List ztextKeys = new ArrayList();
    private List ztextStrings = new ArrayList();

    private WritableRaster theTile;

    private int[] gammaLut;

    private void initGammaLut(int bits) {
        double exp = (double)userExponent / (fileGamma * displayExponent);
        int numSamples = 1 << bits;
        int maxOutSample = (bits == 16) ? 65535 : 255;

        gammaLut = new int[numSamples];
        for (int i = 0; i < numSamples; i++) {
            double gbright = (double)i / (numSamples - 1);
            double gamma = Math.pow(gbright, exp);
            int igamma = (int)(gamma * maxOutSample + 0.5);
            if (igamma > maxOutSample) {
                igamma = maxOutSample;
            }
            gammaLut[i] = igamma;
        }
    }

    private final byte[][] expandBits = {
        null,
        { (byte)0x00, (byte)0xff },
        { (byte)0x00, (byte)0x55, (byte)0xaa, (byte)0xff },
        null,
        { (byte)0x00, (byte)0x11, (byte)0x22, (byte)0x33,
          (byte)0x44, (byte)0x55, (byte)0x66, (byte)0x77,
          (byte)0x88, (byte)0x99, (byte)0xaa, (byte)0xbb,
          (byte)0xcc, (byte)0xdd, (byte)0xee, (byte)0xff }
    };

    private int[] grayLut;

    private void initGrayLut(int bits) {
        int len = 1 << bits;
        grayLut = new int[len];

        if (performGammaCorrection) {
            System.arraycopy(gammaLut, 0, grayLut, 0, len);
        } else {
            for (int i = 0; i < len; i++) {
                grayLut[i] = expandBits[bits][i];
            }
        }
    }

    public PNGImage(InputStream stream) throws IOException {
        DataInputStream distream = new DataInputStream(stream);
        long magic = distream.readLong();
        if (magic != PNG_SIGNATURE) {
            throw new IOException("Not a png file");
        }
        while (true) {
            String chunkType = PNGChunk.getChunkType(distream);
            if (chunkType.equals(PNGChunk.ChunkType.IHDR.name())) {
                PNGChunk chunk = PNGChunk.readChunk(distream);
                parse_IHDR_chunk(chunk);
            } else if (chunkType.equals(PNGChunk.ChunkType.pHYs.name())) {
                PNGChunk chunk = PNGChunk.readChunk(distream);
                parse_pHYs_chunk(chunk);
                return;
            } else if (chunkType.equals(PNGChunk.ChunkType.IEND.name())) {
                return;
            } else {
                PNGChunk.readChunk(distream);
            }
        }
    }

    public PNGImage(InputStream stream, PNGDecodeParam decodeParam)
        throws IOException {

        if (!stream.markSupported()) {
            stream = new BufferedInputStream(stream);
        }
        DataInputStream distream = new DataInputStream(stream);

        if (decodeParam == null) {
            decodeParam = new PNGDecodeParam();
        }
        this.decodeParam = decodeParam;

        // Get parameter values
        this.suppressAlpha = decodeParam.getSuppressAlpha();
        this.expandPalette = decodeParam.getExpandPalette();
        this.output8BitGray = decodeParam.getOutput8BitGray();
        this.expandGrayAlpha = decodeParam.getExpandGrayAlpha();
        if (decodeParam.getPerformGammaCorrection()) {
            this.userExponent = decodeParam.getUserExponent();
            this.displayExponent = decodeParam.getDisplayExponent();
            performGammaCorrection = true;
            output8BitGray = true;
        }
        this.generateEncodeParam = decodeParam.getGenerateEncodeParam();

        if (emitProperties) {
            properties.put("file_type", "PNG v. 1.0");
        }

        try {
            long magic = distream.readLong();
            if (magic != PNG_SIGNATURE) {
                String msg = PropertyUtil.getString("PNGImageDecoder0");
                throw new RuntimeException(msg);
            }
        } catch (IOException ioe) {
            ioe.printStackTrace();
            String msg = PropertyUtil.getString("PNGImageDecoder1");
            throw new RuntimeException(msg);
        }

        do {
//            try {
                PNGChunk chunk;

                String chunkType = PNGChunk.getChunkType(distream);
                if (chunkType.equals(PNGChunk.ChunkType.IHDR.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_IHDR_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.PLTE.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_PLTE_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.IDAT.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    streamVec.add(new ByteArrayInputStream(chunk.getData()));
                } else if (chunkType.equals(PNGChunk.ChunkType.IEND.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    try {
                        parse_IEND_chunk(chunk);
                    } catch (Exception e) {
                        e.printStackTrace();
                        String msg = PropertyUtil.getString("PNGImageDecoder2");
                        throw new RuntimeException(msg);
                    }
                    break; // fall through to the bottom
                } else if (chunkType.equals(PNGChunk.ChunkType.bKGD.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_bKGD_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.cHRM.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_cHRM_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.gAMA.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_gAMA_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.hIST.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_hIST_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.iCCP.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_iCCP_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.pHYs.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_pHYs_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.sBIT.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_sBIT_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.sRGB.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_sRGB_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.tEXt.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_tEXt_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.tIME.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_tIME_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.tRNS.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_tRNS_chunk(chunk);
                } else if (chunkType.equals(PNGChunk.ChunkType.zTXt.name())) {
                    chunk = PNGChunk.readChunk(distream);
                    parse_zTXt_chunk(chunk);
                } else {
                    chunk = PNGChunk.readChunk(distream);
                    // Output the chunk data in raw form

                    String type = chunk.getTypeString();
                    byte[] data = chunk.getData();
                    if (encodeParam != null) {
                        encodeParam.addPrivateChunk(type, data);
                    }
                    if (emitProperties) {
                        String key = "chunk_" + chunkIndex++ + ':' + type;
                        properties.put(key.toLowerCase(Locale.getDefault()), data);
                    }
                }
//            } catch (Exception e) {
//                e.printStackTrace();
//                String msg = PropertyUtil.getString("PNGImageDecoder2");
//                throw new RuntimeException(msg);
//            }
        } while (true);

        // Final post-processing

        if (significantBits == null) {
            significantBits = new int[inputBands];
            for (int i = 0; i < inputBands; i++) {
                significantBits[i] = bitDepth;
            }

            if (emitProperties) {
                properties.put("significant_bits", significantBits);
            }
        }
    }

    private void parse_IHDR_chunk(PNGChunk chunk) {
        tileWidth = width = chunk.getInt4(0);
        tileHeight = height = chunk.getInt4(4);

        bitDepth = chunk.getInt1(8);

        if ((bitDepth != 1) && (bitDepth != 2) && (bitDepth != 4)
            && (bitDepth != 8) && (bitDepth != 16)) {
            // Error -- bad bit depth
            String msg = PropertyUtil.getString("PNGImageDecoder3");
            throw new RuntimeException(msg);
        }
        maxOpacity = (1 << bitDepth) - 1;

        colorType = chunk.getInt1(9);
        if ((colorType != PNG_COLOR_GRAY)
            && (colorType != PNG_COLOR_RGB)
            && (colorType != PNG_COLOR_PALETTE)
            && (colorType != PNG_COLOR_GRAY_ALPHA)
            && (colorType != PNG_COLOR_RGB_ALPHA)) {
            System.out.println(PropertyUtil.getString("PNGImageDecoder4"));
        }

        if ((colorType == PNG_COLOR_RGB) && (bitDepth < 8)) {
            // Error -- RGB images must have 8 or 16 bits
            String msg = PropertyUtil.getString("PNGImageDecoder5");
            throw new RuntimeException(msg);
        }

        if ((colorType == PNG_COLOR_PALETTE) && (bitDepth == 16)) {
            // Error -- palette images must have < 16 bits
            String msg = PropertyUtil.getString("PNGImageDecoder6");
            throw new RuntimeException(msg);
        }

        if ((colorType == PNG_COLOR_GRAY_ALPHA) && (bitDepth < 8)) {
            // Error -- gray/alpha images must have >= 8 bits
            String msg = PropertyUtil.getString("PNGImageDecoder7");
            throw new RuntimeException(msg);
        }

        if ((colorType == PNG_COLOR_RGB_ALPHA) && (bitDepth < 8)) {
            // Error -- RGB/alpha images must have >= 8 bits
            String msg = PropertyUtil.getString("PNGImageDecoder8");
            throw new RuntimeException(msg);
        }

        if (emitProperties) {
            properties.put("color_type", colorTypeNames[colorType]);
        }

        if (generateEncodeParam) {
            if (colorType == PNG_COLOR_PALETTE) {
                encodeParam = new PNGEncodeParam.Palette();
            } else if (colorType == PNG_COLOR_GRAY
                       || colorType == PNG_COLOR_GRAY_ALPHA) {
                encodeParam = new PNGEncodeParam.Gray();
            } else {
                encodeParam = new PNGEncodeParam.RGB();
            }
            decodeParam.setEncodeParam(encodeParam);
        }

        if (encodeParam != null) {
            encodeParam.setBitDepth(bitDepth);
        }
        if (emitProperties) {
            properties.put("bit_depth", bitDepth);
        }

        if (performGammaCorrection) {
            // Assume file gamma is 1/2.2 unless we get a gAMA chunk
            float gamma = (1.0F / 2.2F) * (displayExponent / userExponent);
            if (encodeParam != null) {
                encodeParam.setGamma(gamma);
            }
            if (emitProperties) {
                properties.put("gamma", gamma);
            }
        }

        compressionMethod = chunk.getInt1(10);
        if (compressionMethod != 0) {
            // Error -- only know about compression method 0
            String msg = PropertyUtil.getString("PNGImageDecoder9");
            throw new RuntimeException(msg);
        }

        filterMethod = chunk.getInt1(11);
        if (filterMethod != 0) {
            // Error -- only know about filter method 0
            String msg = PropertyUtil.getString("PNGImageDecoder10");
            throw new RuntimeException(msg);
        }

        interlaceMethod = chunk.getInt1(12);
        if (interlaceMethod == 0) {
            if (encodeParam != null) {
                encodeParam.setInterlacing(false);
            }
            if (emitProperties) {
                properties.put("interlace_method", "None");
            }
        } else if (interlaceMethod == 1) {
            if (encodeParam != null) {
                encodeParam.setInterlacing(true);
            }
            if (emitProperties) {
                properties.put("interlace_method", "Adam7");
            }
        } else {
            // Error -- only know about Adam7 interlacing
            String msg = PropertyUtil.getString("PNGImageDecoder11");
            throw new RuntimeException(msg);
        }

        bytesPerPixel = (bitDepth == 16) ? 2 : 1;

        switch (colorType) {
        case PNG_COLOR_GRAY:
            inputBands = 1;
            outputBands = 1;

            if (output8BitGray && (bitDepth < 8)) {
                postProcess = POST_GRAY_LUT;
            } else if (performGammaCorrection) {
                postProcess = POST_GAMMA;
            } else {
                postProcess = POST_NONE;
            }
            break;

        case PNG_COLOR_RGB:
            inputBands = 3;
            bytesPerPixel *= 3;
            outputBands = 3;

            if (performGammaCorrection) {
                postProcess = POST_GAMMA;
            } else {
                postProcess = POST_NONE;
            }
            break;

        case PNG_COLOR_PALETTE:
            inputBands = 1;
            bytesPerPixel = 1;
            outputBands = expandPalette ? 3 : 1;

            if (expandPalette) {
                postProcess = POST_PALETTE_TO_RGB;
            } else {
                postProcess = POST_NONE;
            }
            break;

        case PNG_COLOR_GRAY_ALPHA:
            inputBands = 2;
            bytesPerPixel *= 2;

            if (suppressAlpha) {
                outputBands = 1;
                postProcess = POST_REMOVE_GRAY_TRANS;
            } else {
                if (performGammaCorrection) {
                    postProcess = POST_GAMMA;
                } else {
                    postProcess = POST_NONE;
                }
                if (expandGrayAlpha) {
                    postProcess |= POST_EXP_MASK;
                    outputBands = 4;
                } else {
                    outputBands = 2;
                }
            }
            break;

        case PNG_COLOR_RGB_ALPHA:
            inputBands = 4;
            bytesPerPixel *= 4;
            outputBands = (!suppressAlpha) ? 4 : 3;

            if (suppressAlpha) {
                postProcess = POST_REMOVE_RGB_TRANS;
            } else if (performGammaCorrection) {
                postProcess = POST_GAMMA;
            } else {
                postProcess = POST_NONE;
            }
            break;
        }
    }

    private void parse_IEND_chunk(PNGChunk chunk) throws Exception {
        // Store text strings
        int textLen = textKeys.size();
        String[] textArray = new String[2 * textLen];
        for (int i = 0; i < textLen; i++) {
            String key = (String)textKeys.get(i);
            String val = (String)textStrings.get(i);
            textArray[2 * i] = key;
            textArray[2 * i + 1] = val;
            if (emitProperties) {
                String uniqueKey = "text_" + i + ':' + key;
                properties.put(uniqueKey.toLowerCase(Locale.getDefault()), val);
            }
        }
        if (encodeParam != null) {
            encodeParam.setText(textArray);
        }

        // Store compressed text strings
        int ztextLen = ztextKeys.size();
        String[] ztextArray = new String[2 * ztextLen];
        for (int i = 0; i < ztextLen; i++) {
            String key = (String)ztextKeys.get(i);
            String val = (String)ztextStrings.get(i);
            ztextArray[2 * i] = key;
            ztextArray[2 * i + 1] = val;
            if (emitProperties) {
                String uniqueKey = "ztext_" + i + ':' + key;
                properties.put(uniqueKey.toLowerCase(Locale.getDefault()), val);
            }
        }
        if (encodeParam != null) {
            encodeParam.setCompressedText(ztextArray);
        }

        // Parse prior IDAT chunks
        InputStream seqStream =
            new SequenceInputStream(Collections.enumeration(streamVec));
        InputStream infStream =
            new InflaterInputStream(seqStream, new Inflater());
        dataStream = new DataInputStream(infStream);

        // Create an empty WritableRaster
        int depth = bitDepth;
        if ((colorType == PNG_COLOR_GRAY)
            && (bitDepth < 8) && output8BitGray) {
            depth = 8;
        }
        if ((colorType == PNG_COLOR_PALETTE) && expandPalette) {
            depth = 8;
        }
        int bytesPerRow = (outputBands * width * depth + 7) / 8;
        int scanlineStride =
            (depth == 16) ? (bytesPerRow / 2) : bytesPerRow;

        theTile = createRaster(width, height, outputBands,
                               scanlineStride,
                               depth);

        if (performGammaCorrection && (gammaLut == null)) {
            initGammaLut(bitDepth);
        }
        if ((postProcess == POST_GRAY_LUT)
            || (postProcess == POST_GRAY_LUT_ADD_TRANS)
            || (postProcess == POST_GRAY_LUT_ADD_TRANS_EXP)) {
            initGrayLut(bitDepth);
        }

        decodeImage(interlaceMethod == 1);
        sampleModel = theTile.getSampleModel();

        if ((colorType == PNG_COLOR_PALETTE) && !expandPalette) {
            if (outputHasAlphaPalette) {
                colorModel = new IndexColorModel(bitDepth,
                                                 paletteEntries,
                                                 redPalette,
                                                 greenPalette,
                                                 bluePalette,
                                                 alphaPalette);
            } else {
                colorModel = new IndexColorModel(bitDepth,
                                                 paletteEntries,
                                                 redPalette,
                                                 greenPalette,
                                                 bluePalette);
            }
        } else if ((colorType == PNG_COLOR_GRAY)
                   && (bitDepth < 8) && !output8BitGray) {
            byte[] palette = expandBits[bitDepth];
            colorModel = new IndexColorModel(bitDepth,
                                             palette.length,
                                             palette,
                                             palette,
                                             palette);
        } else {
            colorModel =
                createComponentColorModel(sampleModel);
        }
    }

    private static final int[] GrayBits8 = { 8 };
    private static final ComponentColorModel colorModelGray8 =
        new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_GRAY),
                                GrayBits8, false, false,
                                Transparency.OPAQUE,
                                DataBuffer.TYPE_BYTE);

    private static final int[] GrayAlphaBits8 = { 8, 8 };
    private static final ComponentColorModel colorModelGrayAlpha8 =
        new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_GRAY),
                                GrayAlphaBits8, true, false,
                                Transparency.TRANSLUCENT,
                                DataBuffer.TYPE_BYTE);

    private static final int[] GrayBits16 = { 16 };
    private static final ComponentColorModel colorModelGray16 =
        new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_GRAY),
                                GrayBits16, false, false,
                                Transparency.OPAQUE,
                                DataBuffer.TYPE_USHORT);

    private static final int[] GrayAlphaBits16 = { 16, 16 };
    private static final ComponentColorModel colorModelGrayAlpha16 =
        new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_GRAY),
                                GrayAlphaBits16, true, false,
                                Transparency.TRANSLUCENT,
                                DataBuffer.TYPE_USHORT);

    private static final int[] GrayBits32 = { 32 };
    private static final ComponentColorModel colorModelGray32 =
        new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_GRAY),
                                GrayBits32, false, false,
                                Transparency.OPAQUE,
                                DataBuffer.TYPE_INT);

    private static final int[] GrayAlphaBits32 = { 32, 32 };
    private static final ComponentColorModel colorModelGrayAlpha32 =
        new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_GRAY),
                                GrayAlphaBits32, true, false,
                                Transparency.TRANSLUCENT,
                                DataBuffer.TYPE_INT);

    private static final int[] RGBBits8 = { 8, 8, 8 };
    private static final ComponentColorModel colorModelRGB8 =
      new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB),
                              RGBBits8, false, false,
                              Transparency.OPAQUE,
                              DataBuffer.TYPE_BYTE);

    private static final int[] RGBABits8 = { 8, 8, 8, 8 };
    private static final ComponentColorModel colorModelRGBA8 =
      new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB),
                              RGBABits8, true, false,
                              Transparency.TRANSLUCENT,
                              DataBuffer.TYPE_BYTE);

    private static final int[] RGBBits16 = { 16, 16, 16 };
    private static final ComponentColorModel colorModelRGB16 =
      new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB),
                              RGBBits16, false, false,
                              Transparency.OPAQUE,
                              DataBuffer.TYPE_USHORT);

    private static final int[] RGBABits16 = { 16, 16, 16, 16 };
    private static final ComponentColorModel colorModelRGBA16 =
      new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB),
                              RGBABits16, true, false,
                              Transparency.TRANSLUCENT,
                              DataBuffer.TYPE_USHORT);

    private static final int[] RGBBits32 = { 32, 32, 32 };
    private static final ComponentColorModel colorModelRGB32 =
      new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB),
                              RGBBits32, false, false,
                              Transparency.OPAQUE,
                              DataBuffer.TYPE_INT);

    private static final int[] RGBABits32 = { 32, 32, 32, 32 };
    private static final ComponentColorModel colorModelRGBA32 =
      new ComponentColorModel(ColorSpace.getInstance(ColorSpace.CS_sRGB),
                              RGBABits32, true, false,
                              Transparency.TRANSLUCENT,
                              DataBuffer.TYPE_INT);
    
A convenience method to create an instance of
ComponentColorModel suitable for use with the
given SampleModel.  The SampleModel
should have a data type of DataBuffer.TYPE_BYTE,
TYPE_USHORT, or TYPE_INT and between
1 and 4 bands.  Depending on the number of bands of the
SampleModel, either a gray, gray+alpha, rgb, or
rgb+alpha ColorModel is returned.

/**
     * A convenience method to create an instance of
     * <code>ComponentColorModel</code> suitable for use with the
     * given <code>SampleModel</code>.  The <code>SampleModel</code>
     * should have a data type of <code>DataBuffer.TYPE_BYTE</code>,
     * <code>TYPE_USHORT</code>, or <code>TYPE_INT</code> and between
     * 1 and 4 bands.  Depending on the number of bands of the
     * <code>SampleModel</code>, either a gray, gray+alpha, rgb, or
     * rgb+alpha <code>ColorModel</code> is returned.
     */
    public static ColorModel createComponentColorModel(SampleModel sm) {
        int type = sm.getDataType();
        int bands = sm.getNumBands();
        ComponentColorModel cm = null;

        if (type == DataBuffer.TYPE_BYTE) {
            switch (bands) {
            case 1:
                cm = colorModelGray8;
                break;
            case 2:
                cm = colorModelGrayAlpha8;
                break;
            case 3:
                cm = colorModelRGB8;
                break;
            case 4:
                cm = colorModelRGBA8;
                break;
            }
        } else if (type == DataBuffer.TYPE_USHORT) {
            switch (bands) {
            case 1:
                cm = colorModelGray16;
                break;
            case 2:
                cm = colorModelGrayAlpha16;
                break;
            case 3:
                cm = colorModelRGB16;
                break;
            case 4:
                cm = colorModelRGBA16;
                break;
            }
        } else if (type == DataBuffer.TYPE_INT) {
            switch (bands) {
            case 1:
                cm = colorModelGray32;
                break;
            case 2:
                cm = colorModelGrayAlpha32;
                break;
            case 3:
                cm = colorModelRGB32;
                break;
            case 4:
                cm = colorModelRGBA32;
                break;
            }
        }

        return cm;
    }

    private void parse_PLTE_chunk(PNGChunk chunk) {
        paletteEntries = chunk.getLength() / 3;
        redPalette = new byte[paletteEntries];
        greenPalette = new byte[paletteEntries];
        bluePalette = new byte[paletteEntries];

        int pltIndex = 0;

        // gAMA chunk must precede PLTE chunk
        if (performGammaCorrection) {
            if (gammaLut == null) {
                initGammaLut(bitDepth == 16 ? 16 : 8);
            }

            for (int i = 0; i < paletteEntries; i++) {
                byte r = chunk.getByte(pltIndex++);
                byte g = chunk.getByte(pltIndex++);
                byte b = chunk.getByte(pltIndex++);

                redPalette[i] = (byte)gammaLut[r & 0xff];
                greenPalette[i] = (byte)gammaLut[g & 0xff];
                bluePalette[i] = (byte)gammaLut[b & 0xff];
            }
        } else {
            for (int i = 0; i < paletteEntries; i++) {
                redPalette[i] = chunk.getByte(pltIndex++);
                greenPalette[i] = chunk.getByte(pltIndex++);
                bluePalette[i] = chunk.getByte(pltIndex++);
            }
        }
    }

    private void parse_bKGD_chunk(PNGChunk chunk) {
        switch (colorType) {
        case PNG_COLOR_PALETTE:
            int bkgdIndex = chunk.getByte(0) & 0xff;

            bkgdRed = redPalette[bkgdIndex] & 0xff;
            bkgdGreen = greenPalette[bkgdIndex] & 0xff;
            bkgdBlue = bluePalette[bkgdIndex] & 0xff;

            if (encodeParam != null) {
                ((PNGEncodeParam.Palette)encodeParam).setBackgroundPaletteIndex(bkgdIndex);
            }
            break;
        case PNG_COLOR_GRAY: case PNG_COLOR_GRAY_ALPHA:
            int bkgdGray = chunk.getInt2(0);
            bkgdRed = bkgdGreen = bkgdBlue = bkgdGray;

            if (encodeParam != null) {
                ((PNGEncodeParam.Gray)encodeParam).setBackgroundGray(bkgdGray);
            }
            break;
        case PNG_COLOR_RGB: case PNG_COLOR_RGB_ALPHA:
            bkgdRed = chunk.getInt2(0);
            bkgdGreen = chunk.getInt2(2);
            bkgdBlue = chunk.getInt2(4);

            int[] bkgdRGB = new int[3];
            bkgdRGB[0] = bkgdRed;
            bkgdRGB[1] = bkgdGreen;
            bkgdRGB[2] = bkgdBlue;
            if (encodeParam != null) {
                ((PNGEncodeParam.RGB)encodeParam).setBackgroundRGB(bkgdRGB);
            }
            break;
        }

        int r = 0;
        int g = 0;
        int b = 0;
        if (bitDepth < 8) {
            r = expandBits[bitDepth][bkgdRed];
            g = expandBits[bitDepth][bkgdGreen];
            b = expandBits[bitDepth][bkgdBlue];
        } else if (bitDepth == 8) {
            r = bkgdRed;
            g = bkgdGreen;
            b = bkgdBlue;
        } else if (bitDepth == 16) {
            r = bkgdRed >> 8;
            g = bkgdGreen >> 8;
            b = bkgdBlue >> 8;
        }
        if (emitProperties) {
            properties.put("background_color", new Color(r, g, b));
        }
    }

    private void parse_cHRM_chunk(PNGChunk chunk) {
        // If an sRGB chunk exists, ignore cHRM chunks
        if (sRGBRenderingIntent != -1) {
            return;
        }

        chromaticity = new float[8];
        chromaticity[0] = chunk.getInt4(0) / 100000.0F;
        chromaticity[1] = chunk.getInt4(4) / 100000.0F;
        chromaticity[2] = chunk.getInt4(8) / 100000.0F;
        chromaticity[3] = chunk.getInt4(12) / 100000.0F;
        chromaticity[4] = chunk.getInt4(16) / 100000.0F;
        chromaticity[5] = chunk.getInt4(20) / 100000.0F;
        chromaticity[6] = chunk.getInt4(24) / 100000.0F;
        chromaticity[7] = chunk.getInt4(28) / 100000.0F;

        if (encodeParam != null) {
            encodeParam.setChromaticity(chromaticity);
        }
        if (emitProperties) {
            properties.put("white_point_x", chromaticity[0]);
            properties.put("white_point_y", chromaticity[1]);
            properties.put("red_x", chromaticity[2]);
            properties.put("red_y", chromaticity[3]);
            properties.put("green_x", chromaticity[4]);
            properties.put("green_y", chromaticity[5]);
            properties.put("blue_x", chromaticity[6]);
            properties.put("blue_y", chromaticity[7]);
        }
    }

    private void parse_gAMA_chunk(PNGChunk chunk) {
        // If an sRGB chunk exists, ignore gAMA chunks
        if (sRGBRenderingIntent != -1) {
            return;
        }

        fileGamma = chunk.getInt4(0) / 100000.0F;

        float exp =
            performGammaCorrection ? displayExponent / userExponent : 1.0F;
        if (encodeParam != null) {
            encodeParam.setGamma(fileGamma * exp);
        }
        if (emitProperties) {
            properties.put("gamma", fileGamma * exp);
        }
    }

    private void parse_hIST_chunk(PNGChunk chunk) {
        if (redPalette == null) {
            String msg = PropertyUtil.getString("PNGImageDecoder18");
            throw new RuntimeException(msg);
        }

        int length = redPalette.length;
        int[] hist = new int[length];
        for (int i = 0; i < length; i++) {
            hist[i] = chunk.getInt2(2 * i);
        }

        if (encodeParam != null) {
            encodeParam.setPaletteHistogram(hist);
        }
    }

    private void parse_iCCP_chunk(PNGChunk chunk) {
//        String name = "";  // todo simplify this
//        byte b;

//        int textIndex = 0;
//        while ((b = chunk.getByte(textIndex++)) != 0) {
//            name += (char)b;
//        }
    }

    private void parse_pHYs_chunk(PNGChunk chunk) {
        xPixelsPerUnit = chunk.getInt4(0);
        yPixelsPerUnit = chunk.getInt4(4);
        unitSpecifier = chunk.getInt1(8);

        if (encodeParam != null) {
            encodeParam.setPhysicalDimension(xPixelsPerUnit,
                                             yPixelsPerUnit,
                                             unitSpecifier);
        }
        if (emitProperties) {
            properties.put("x_pixels_per_unit", xPixelsPerUnit);
            properties.put("y_pixels_per_unit", yPixelsPerUnit);
            properties.put("pixel_aspect_ratio",
                    (float) xPixelsPerUnit / yPixelsPerUnit);
            if (unitSpecifier == 1) {
                properties.put("pixel_units", "Meters");
            } else if (unitSpecifier != 0) {
                // Error -- unit specifier must be 0 or 1
                String msg = PropertyUtil.getString("PNGImageDecoder12");
                throw new RuntimeException(msg);
            }
        }
    }

    private void parse_sBIT_chunk(PNGChunk chunk) {
        if (colorType == PNG_COLOR_PALETTE) {
            significantBits = new int[3];
        } else {
            significantBits = new int[inputBands];
        }
        for (int i = 0; i < significantBits.length; i++) {
            int bits = chunk.getByte(i);
            int depth = (colorType == PNG_COLOR_PALETTE) ? 8 : bitDepth;
            if (bits <= 0 || bits > depth) {
                // Error -- significant bits must be between 0 and
                // image bit depth.
                String msg = PropertyUtil.getString("PNGImageDecoder13");
                throw new RuntimeException(msg);
            }
            significantBits[i] = bits;
        }

        if (encodeParam != null) {
            encodeParam.setSignificantBits(significantBits);
        }
        if (emitProperties) {
            properties.put("significant_bits", significantBits);
        }
    }

    private void parse_sRGB_chunk(PNGChunk chunk) {
        sRGBRenderingIntent = chunk.getByte(0);

        // The presence of an sRGB chunk implies particular
        // settings for gamma and chroma.
        fileGamma = 45455 / 100000.0F;

        chromaticity = new float[8];
        chromaticity[0] = 31270 / 10000.0F;
        chromaticity[1] = 32900 / 10000.0F;
        chromaticity[2] = 64000 / 10000.0F;
        chromaticity[3] = 33000 / 10000.0F;
        chromaticity[4] = 30000 / 10000.0F;
        chromaticity[5] = 60000 / 10000.0F;
        chromaticity[6] = 15000 / 10000.0F;
        chromaticity[7] =  6000 / 10000.0F;

        if (performGammaCorrection) {
            // File gamma is 1/2.2
            float gamma = fileGamma * (displayExponent / userExponent);
            if (encodeParam != null) {
                encodeParam.setGamma(gamma);
                encodeParam.setChromaticity(chromaticity);
            }
            if (emitProperties) {
                properties.put("gamma", gamma);
                properties.put("white_point_x", chromaticity[0]);
                properties.put("white_point_y", chromaticity[1]);
                properties.put("red_x", chromaticity[2]);
                properties.put("red_y", chromaticity[3]);
                properties.put("green_x", chromaticity[4]);
                properties.put("green_y", chromaticity[5]);
                properties.put("blue_x", chromaticity[6]);
                properties.put("blue_y", chromaticity[7]);
            }
        }
    }

    private void parse_tEXt_chunk(PNGChunk chunk) {

        byte b;
        StringBuffer key = new StringBuffer();
        int textIndex = 0;
        while ((b = chunk.getByte(textIndex++)) != 0) {
            key.append((char)b);
        }

        StringBuilder value = new StringBuilder();
        for (int i = textIndex; i < chunk.getLength(); i++) {
            value.append((char)chunk.getByte(i));
        }

        textKeys.add(key.toString());
        textStrings.add(value.toString());
    }

    private void parse_tIME_chunk(PNGChunk chunk) {
        int year = chunk.getInt2(0);
        int month = chunk.getInt1(2) - 1;
        int day = chunk.getInt1(3);
        int hour = chunk.getInt1(4);
        int minute = chunk.getInt1(5);
        int second = chunk.getInt1(6);

        TimeZone gmt = TimeZone.getTimeZone("GMT");

        GregorianCalendar cal = new GregorianCalendar(gmt);
        cal.set(year, month, day,
                hour, minute, second);
        Date date = cal.getTime();

        if (encodeParam != null) {
            encodeParam.setModificationTime(date);
        }
        if (emitProperties) {
            properties.put("timestamp", date);
        }
    }

    private void parse_tRNS_chunk(PNGChunk chunk) {
        if (colorType == PNG_COLOR_PALETTE) {
            int entries = chunk.getLength();
            if (entries > paletteEntries) {
                // Error -- mustn't have more alpha than RGB palette entries
                String msg = PropertyUtil.getString("PNGImageDecoder14");
                throw new RuntimeException(msg);
            }

            // Load beginning of palette from the chunk
            alphaPalette = new byte[paletteEntries];
            for (int i = 0; i < entries; i++) {
                alphaPalette[i] = chunk.getByte(i);
            }

            // Fill rest of palette with 255
            for (int i = entries; i < paletteEntries; i++) {
                alphaPalette[i] = (byte)255;
            }

            if (!suppressAlpha) {
                if (expandPalette) {
                    postProcess = POST_PALETTE_TO_RGBA;
                    outputBands = 4;
                } else {
                    outputHasAlphaPalette = true;
                }
            }
        } else if (colorType == PNG_COLOR_GRAY) {
            grayTransparentAlpha = chunk.getInt2(0);

            if (!suppressAlpha) {
                if (bitDepth < 8) {
                    output8BitGray = true;
                    maxOpacity = 255;
                    postProcess = POST_GRAY_LUT_ADD_TRANS;
                } else {
                    postProcess = POST_ADD_GRAY_TRANS;
                }

                if (expandGrayAlpha) {
                    outputBands = 4;
                    postProcess |= POST_EXP_MASK;
                } else {
                    outputBands = 2;
                }

                if (encodeParam != null) {
                    ((PNGEncodeParam.Gray)encodeParam).setTransparentGray(grayTransparentAlpha);
                }
            }
        } else if (colorType == PNG_COLOR_RGB) {
            redTransparentAlpha = chunk.getInt2(0);
            greenTransparentAlpha = chunk.getInt2(2);
            blueTransparentAlpha = chunk.getInt2(4);

            if (!suppressAlpha) {
                outputBands = 4;
                postProcess = POST_ADD_RGB_TRANS;

                if (encodeParam != null) {
                    int[] rgbTrans = new int[3];
                    rgbTrans[0] = redTransparentAlpha;
                    rgbTrans[1] = greenTransparentAlpha;
                    rgbTrans[2] = blueTransparentAlpha;
                    ((PNGEncodeParam.RGB)encodeParam).setTransparentRGB(rgbTrans);
                }
            }
        } else if (colorType == PNG_COLOR_GRAY_ALPHA
                   || colorType == PNG_COLOR_RGB_ALPHA) {
            // Error -- GA or RGBA image can't have a tRNS chunk.
            String msg = PropertyUtil.getString("PNGImageDecoder15");
            throw new RuntimeException(msg);
        }
    }

    private void parse_zTXt_chunk(PNGChunk chunk) {

        int textIndex = 0;
        StringBuffer key = new StringBuffer();
        byte b;
        while ((b = chunk.getByte(textIndex++)) != 0) {
            key.append((char)b);
        }

        // skip method
        textIndex++;

        StringBuffer value = new StringBuffer();
        try {
            int length = chunk.getLength() - textIndex;
            byte[] data = chunk.getData();
            InputStream cis =
                new ByteArrayInputStream(data, textIndex, length);
            InputStream iis = new InflaterInputStream(cis);

            int c;
            while ((c = iis.read()) != -1) {
                value.append((char)c);
            }

            ztextKeys.add(key.toString());
            ztextStrings.add(value.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private WritableRaster createRaster(int width, int height, int bands,
                                        int scanlineStride,
                                        int bitDepth) {

        DataBuffer dataBuffer;
        WritableRaster ras = null;
        Point origin = new Point(0, 0);
        if ((bitDepth < 8) && (bands == 1)) {
            dataBuffer = new DataBufferByte(height * scanlineStride);
            ras = Raster.createPackedRaster(dataBuffer,
                                            width, height,
                                            bitDepth,
                                            origin);
        } else if (bitDepth <= 8) {
            dataBuffer = new DataBufferByte(height * scanlineStride);
           ras = Raster.createInterleavedRaster(dataBuffer,
                                                 width, height,
                                                 scanlineStride,
                                                 bands,
                                                 bandOffsets[bands],
                                                 origin);
        } else {
            dataBuffer = new DataBufferUShort(height * scanlineStride);
            ras = Raster.createInterleavedRaster(dataBuffer,
                                                 width, height,
                                                 scanlineStride,
                                                 bands,
                                                 bandOffsets[bands],
                                                 origin);
        }

        return ras;
    }

    // Data filtering methods

    private static void decodeSubFilter(byte[] curr, int count, int bpp) {
        for (int i = bpp; i < count; i++) {
            int val;

            val = curr[i] & 0xff;
            val += curr[i - bpp] & 0xff;

            curr[i] = (byte)val;
        }
    }

    private static void decodeUpFilter(byte[] curr, byte[] prev,
                                       int count) {
        for (int i = 0; i < count; i++) {
            int raw = curr[i] & 0xff;
            int prior = prev[i] & 0xff;

            curr[i] = (byte)(raw + prior);
        }
    }

    private static void decodeAverageFilter(byte[] curr, byte[] prev,
                                            int count, int bpp) {
        int raw;
        int priorPixel;
        int priorRow;

        for (int i = 0; i < bpp; i++) {
            raw = curr[i] & 0xff;
            priorRow = prev[i] & 0xff;

            curr[i] = (byte)(raw + priorRow / 2);
        }

        for (int i = bpp; i < count; i++) {
            raw = curr[i] & 0xff;
            priorPixel = curr[i - bpp] & 0xff;
            priorRow = prev[i] & 0xff;

            curr[i] = (byte)(raw + (priorPixel + priorRow) / 2);
        }
    }

    private static void decodePaethFilter(byte[] curr, byte[] prev,
                                          int count, int bpp) {
        int raw;
        int priorPixel;
        int priorRow;
        int priorRowPixel;

        for (int i = 0; i < bpp; i++) {
            raw = curr[i] & 0xff;
            priorRow = prev[i] & 0xff;

            curr[i] = (byte)(raw + priorRow);
        }

        for (int i = bpp; i < count; i++) {
            raw = curr[i] & 0xff;
            priorPixel = curr[i - bpp] & 0xff;
            priorRow = prev[i] & 0xff;
            priorRowPixel = prev[i - bpp] & 0xff;

            curr[i] = (byte)(raw + PNGEncodeParam.paethPredictor(priorPixel,
                                                  priorRow,
                                                  priorRowPixel));
        }
    }

    private void processPixels(int process,
                               Raster src, WritableRaster dst,
                               int xOffset, int step, int y, int width) {
        int srcX;
        int dstX;

        // Create an array suitable for holding one pixel
        int[] ps = src.getPixel(0, 0, (int[])null);
        int[] pd = dst.getPixel(0, 0, (int[])null);

        dstX = xOffset;
        switch (process) {
        case POST_NONE:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);
                dst.setPixel(dstX, y, ps);
                dstX += step;
            }
            break;

        case POST_GAMMA:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                for (int i = 0; i < inputBands; i++) {
                    int x = ps[i];
                    ps[i] = gammaLut[x];
                }

                dst.setPixel(dstX, y, ps);
                dstX += step;
            }
            break;

        case POST_GRAY_LUT:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                pd[0] = grayLut[ps[0]];

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_GRAY_LUT_ADD_TRANS:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                pd[0] = grayLut[val];
                if (val == grayTransparentAlpha) {
                    pd[1] = 0;
                } else {
                    pd[1] = maxOpacity;
                }

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_PALETTE_TO_RGB:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                pd[0] = redPalette[val];
                pd[1] = greenPalette[val];
                pd[2] = bluePalette[val];

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_PALETTE_TO_RGBA:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                pd[0] = redPalette[val];
                pd[1] = greenPalette[val];
                pd[2] = bluePalette[val];
                pd[3] = alphaPalette[val];

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_ADD_GRAY_TRANS:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                if (performGammaCorrection) {
                    val = gammaLut[val];
                }
                pd[0] = val;
                if (val == grayTransparentAlpha) {
                    pd[1] = 0;
                } else {
                    pd[1] = maxOpacity;
                }

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_ADD_RGB_TRANS:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int r = ps[0];
                int g = ps[1];
                int b = ps[2];
                if (performGammaCorrection) {
                    pd[0] = gammaLut[r];
                    pd[1] = gammaLut[g];
                    pd[2] = gammaLut[b];
                } else {
                    pd[0] = r;
                    pd[1] = g;
                    pd[2] = b;
                }
                if ((r == redTransparentAlpha)
                    && (g == greenTransparentAlpha)
                    && (b == blueTransparentAlpha)) {
                    pd[3] = 0;
                } else {
                    pd[3] = maxOpacity;
                }

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_REMOVE_GRAY_TRANS:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int g = ps[0];
                if (performGammaCorrection) {
                    pd[0] = gammaLut[g];
                } else {
                    pd[0] = g;
                }

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_REMOVE_RGB_TRANS:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int r = ps[0];
                int g = ps[1];
                int b = ps[2];
                if (performGammaCorrection) {
                    pd[0] = gammaLut[r];
                    pd[1] = gammaLut[g];
                    pd[2] = gammaLut[b];
                } else {
                    pd[0] = r;
                    pd[1] = g;
                    pd[2] = b;
                }

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_GAMMA_EXP:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                int alpha = ps[1];
                int gamma = gammaLut[val];
                pd[0] = gamma;
                pd[1] = gamma;
                pd[2] = gamma;
                pd[3] = alpha;

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_GRAY_ALPHA_EXP:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                int alpha = ps[1];
                pd[0] = val;
                pd[1] = val;
                pd[2] = val;
                pd[3] = alpha;

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_ADD_GRAY_TRANS_EXP:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                if (performGammaCorrection) {
                    val = gammaLut[val];
                }
                pd[0] = val;
                pd[1] = val;
                pd[2] = val;
                if (val == grayTransparentAlpha) {
                    pd[3] = 0;
                } else {
                    pd[3] = maxOpacity;
                }

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;

        case POST_GRAY_LUT_ADD_TRANS_EXP:
            for (srcX = 0; srcX < width; srcX++) {
                src.getPixel(srcX, 0, ps);

                int val = ps[0];
                int val2 = grayLut[val];
                pd[0] = val2;
                pd[1] = val2;
                pd[2] = val2;
                if (val == grayTransparentAlpha) {
                    pd[3] = 0;
                } else {
                    pd[3] = maxOpacity;
                }

                dst.setPixel(dstX, y, pd);
                dstX += step;
            }
            break;
        }
    }

    
Reads in an image of a given size and returns it as a
WritableRaster.

/**
     * Reads in an image of a given size and returns it as a
     * WritableRaster.
     */
    private void decodePass(WritableRaster imRas,
                            int xOffset, int yOffset,
                            int xStep, int yStep,
                            int passWidth, int passHeight) {
        if ((passWidth == 0) || (passHeight == 0)) {
            return;
        }

        int bytesPerRow = (inputBands * passWidth * bitDepth + 7) / 8;
        int eltsPerRow = (bitDepth == 16) ? bytesPerRow / 2 : bytesPerRow;
        byte[] curr = new byte[bytesPerRow];
        byte[] prior = new byte[bytesPerRow];

        // Create a 1-row tall Raster to hold the data
        WritableRaster passRow =
            createRaster(passWidth, 1, inputBands,
                         eltsPerRow,
                         bitDepth);
        DataBuffer dataBuffer = passRow.getDataBuffer();
        int type = dataBuffer.getDataType();
        byte[] byteData = null;
        short[] shortData = null;
        if (type == DataBuffer.TYPE_BYTE) {
            byteData = ((DataBufferByte)dataBuffer).getData();
        } else {
            shortData = ((DataBufferUShort)dataBuffer).getData();
        }

        // Decode the (sub)image row-by-row
        int srcY;
        int dstY;
        for (srcY = 0, dstY = yOffset;
             srcY < passHeight;
             srcY++, dstY += yStep) {
            // Read the filter type byte and a row of data
            int filter = 0;
            try {
                filter = dataStream.read();
                dataStream.readFully(curr, 0, bytesPerRow);
            } catch (Exception e) {
                e.printStackTrace();
            }

            switch (filter) {
            case PNG_FILTER_NONE:
                break;
            case PNG_FILTER_SUB:
                decodeSubFilter(curr, bytesPerRow, bytesPerPixel);
                break;
            case PNG_FILTER_UP:
                decodeUpFilter(curr, prior, bytesPerRow);
                break;
            case PNG_FILTER_AVERAGE:
                decodeAverageFilter(curr, prior, bytesPerRow, bytesPerPixel);
                break;
            case PNG_FILTER_PAETH:
                decodePaethFilter(curr, prior, bytesPerRow, bytesPerPixel);
                break;
            default:
                // Error -- uknown filter type
                String msg = PropertyUtil.getString("PNGImageDecoder16");
                throw new RuntimeException(msg);
            }

            // Copy data into passRow byte by byte
            if (bitDepth < 16) {
                System.arraycopy(curr, 0, byteData, 0, bytesPerRow);
            } else {
                int idx = 0;
                for (int j = 0; j < eltsPerRow; j++) {
                    shortData[j] =
                        (short)((curr[idx] << 8) | (curr[idx + 1] & 0xff));
                    idx += 2;
                }
            }

            processPixels(postProcess,
                          passRow, imRas, xOffset, xStep, dstY, passWidth);

            // Swap curr and prior
            byte[] tmp = prior;
            prior = curr;
            curr = tmp;
        }
    }

    private void decodeImage(boolean useInterlacing) {
        if (!useInterlacing) {
            decodePass(theTile, 0, 0, 1, 1, width, height);
        } else {
            decodePass(theTile, 0, 0, 8, 8, (width + 7) / 8, (height + 7) / 8);
            decodePass(theTile, 4, 0, 8, 8, (width + 3) / 8, (height + 7) / 8);
            decodePass(theTile, 0, 4, 4, 8, (width + 3) / 4, (height + 3) / 8);
            decodePass(theTile, 2, 0, 4, 4, (width + 1) / 4, (height + 3) / 4);
            decodePass(theTile, 0, 2, 2, 4, (width + 1) / 2, (height + 1) / 4);
            decodePass(theTile, 1, 0, 2, 2, width / 2, (height + 1) / 2);
            decodePass(theTile, 0, 1, 1, 2, width, height / 2);
        }
    }

    // RenderedImage stuff

    public Raster getTile(int tileX, int tileY) {
        if (tileX != 0 || tileY != 0) {
            // Error -- bad tile requested
            String msg = PropertyUtil.getString("PNGImageDecoder17");
            throw new IllegalArgumentException(msg);
        }
        return theTile;
    }
}