gifimagewriter.java

java1.6众多例子参考

/*
 * @(#)GIFImageWriter.java	1.13 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package com.sun.imageio.plugins.gif;

import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.image.ColorModel;
import java.awt.image.ComponentSampleModel;
import java.awt.image.DataBufferByte;
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.IOException;
import java.nio.ByteOrder;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Locale;
import javax.imageio.IIOException;
import javax.imageio.IIOImage;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.spi.ImageWriterSpi;
import javax.imageio.metadata.IIOInvalidTreeException;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.metadata.IIOMetadataFormatImpl;
import javax.imageio.metadata.IIOMetadataNode;
import javax.imageio.stream.ImageOutputStream;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import com.sun.imageio.plugins.common.LZWCompressor;
import com.sun.imageio.plugins.common.PaletteBuilder;

public class GIFImageWriter extends ImageWriter {
    private static final boolean DEBUG = false; // XXX false for release!
    
    static final String STANDARD_METADATA_NAME =
    IIOMetadataFormatImpl.standardMetadataFormatName;

    static final String STREAM_METADATA_NAME =
    GIFWritableStreamMetadata.NATIVE_FORMAT_NAME;
    
    static final String IMAGE_METADATA_NAME =
    GIFWritableImageMetadata.NATIVE_FORMAT_NAME;
    
    /**
     * The <code>output</code> case to an <code>ImageOutputStream</code>.
     */
    private ImageOutputStream stream = null;

    /**
     * Whether a sequence is being written.
     */
    private boolean isWritingSequence = false;

    /**
     * Whether the header has been written.
     */
    private boolean wroteSequenceHeader = false;

    /**
     * The stream metadata of a sequence.
     */
    private GIFWritableStreamMetadata theStreamMetadata = null;

    /**
     * The index of the image being written.
     */
    private int imageIndex = 0;

    /**
     * The number of bits represented by the value which should be a
     * legal length for a color table.
     */
    private static int getNumBits(int value) throws IOException {
        int numBits;
        switch(value) {
        case 2:
            numBits = 1;
            break;
        case 4:
            numBits = 2;
            break;
        case 8:
            numBits = 3;
            break;
        case 16:
            numBits = 4;
            break;
        case 32:
            numBits = 5;
            break;
        case 64:
            numBits = 6;
            break;
        case 128:
            numBits = 7;
            break;
        case 256:
            numBits = 8;
            break;
        default:
            throw new IOException("Bad palette length: "+value+"!");
        }
        
        return numBits;
    }
    
    /**
     * Compute the source region and destination dimensions taking any
     * parameter settings into account.
     */
    private static void computeRegions(Rectangle sourceBounds,
                                       Dimension destSize,
                                       ImageWriteParam p) {
        ImageWriteParam param;
        int periodX = 1;
        int periodY = 1;
        if (p != null) {
            int[] sourceBands = p.getSourceBands();
            if (sourceBands != null &&
                (sourceBands.length != 1 ||
                 sourceBands[0] != 0)) {
                throw new IllegalArgumentException("Cannot sub-band image!");
            }
            
            // Get source region and subsampling factors
            Rectangle sourceRegion = p.getSourceRegion();
            if (sourceRegion != null) {
                // Clip to actual image bounds
                sourceRegion = sourceRegion.intersection(sourceBounds);
                sourceBounds.setBounds(sourceRegion);
            }
            
            // Adjust for subsampling offsets
            int gridX = p.getSubsamplingXOffset();
            int gridY = p.getSubsamplingYOffset();
            sourceBounds.x += gridX;
            sourceBounds.y += gridY;
            sourceBounds.width -= gridX;
            sourceBounds.height -= gridY;
            
            // Get subsampling factors
            periodX = p.getSourceXSubsampling();
            periodY = p.getSourceYSubsampling();
        }
        
        // Compute output dimensions
        destSize.setSize((sourceBounds.width + periodX - 1)/periodX,
                         (sourceBounds.height + periodY - 1)/periodY);
        if (destSize.width <= 0 || destSize.height <= 0) {
            throw new IllegalArgumentException("Empty source region!");
        }
    }

    /**
     * Create a color table from the image ColorModel and SampleModel.
     */
    private static byte[] createColorTable(ColorModel colorModel,
                                           SampleModel sampleModel)
    {
        byte[] colorTable;
        if (colorModel instanceof IndexColorModel) {
            IndexColorModel icm = (IndexColorModel)colorModel;
            int mapSize = icm.getMapSize();

            /**
             * The GIF image format assumes that size of image palette
             * is power of two. We will use closest larger power of two 
             * as size of color table.
             */
            int ctSize = getGifPaletteSize(mapSize);
            
            byte[] reds = new byte[ctSize];
            byte[] greens = new byte[ctSize];
            byte[] blues = new byte[ctSize];
            icm.getReds(reds);
            icm.getGreens(greens);
            icm.getBlues(blues);

            /**
             * fill tail of color component arrays by replica of first color
             * in order to avoid appearance of extra colors in the color table
             */
            for (int i = mapSize; i < ctSize; i++) {
                reds[i] = reds[0];
                greens[i] = greens[0];
                blues[i] = blues[0];
            }

            colorTable = new byte[3*ctSize];
            int idx = 0;
            for (int i = 0; i < ctSize; i++) {
                colorTable[idx++] = reds[i];
                colorTable[idx++] = greens[i];
                colorTable[idx++] = blues[i];
            }
        } else if (sampleModel.getNumBands() == 1) {
            // create gray-scaled color table for single-banded images
            int numBits = sampleModel.getSampleSize()[0];
            if (numBits > 8) {
                numBits = 8;
            }
            int colorTableLength = 3*(1 << numBits);
            colorTable = new byte[colorTableLength];
            for (int i = 0; i < colorTableLength; i++) {
                colorTable[i] = (byte)(i/3);
            }
        } else {
            // We do not have enough information here 
            // to create well-fit color table for RGB image.
            colorTable = null;
        }
        
        return colorTable;
    }
    
    /**
     * According do GIF specification size of clor table (palette here) 
     * must be in range from 2 to 256 and must be power of 2.
     */
    private static int getGifPaletteSize(int x) {
        if (x <= 2) {
            return 2;
        }
        x = x - 1;
        x = x | (x >> 1);
        x = x | (x >> 2);
        x = x | (x >> 4);
        x = x | (x >> 8);
        x = x | (x >> 16);
        return x + 1;
    }


                
    public GIFImageWriter(GIFImageWriterSpi originatingProvider) {
        super(originatingProvider);
        if (DEBUG) {
            System.err.println("GIF Writer is created");
        }
    }
    
    public boolean canWriteSequence() {
        return true;
    }
    
    /**
     * Merges <code>inData</code> into <code>outData</code>. The supplied
     * metadata format name is attempted first and failing that the standard
     * metadata format name is attempted.
     */
    private void convertMetadata(String metadataFormatName,
                                 IIOMetadata inData,
                                 IIOMetadata outData) {
        String formatName = null;
        
        String nativeFormatName = inData.getNativeMetadataFormatName();
        if (nativeFormatName != null &&
            nativeFormatName.equals(metadataFormatName)) {
            formatName = metadataFormatName;
        } else {
            String[] extraFormatNames = inData.getExtraMetadataFormatNames();
            
            if (extraFormatNames != null) {
                for (int i = 0; i < extraFormatNames.length; i++) {
                    if (extraFormatNames[i].equals(metadataFormatName)) {
                        formatName = metadataFormatName;
                        break;
                    }
                }
            }
        }
        
        if (formatName == null &&
            inData.isStandardMetadataFormatSupported()) {
            formatName = STANDARD_METADATA_NAME;
        }
        
        if (formatName != null) {
            try {
                Node root = inData.getAsTree(formatName);
                outData.mergeTree(formatName, root);
            } catch(IIOInvalidTreeException e) {
                // ignore
            }
        }
    }
    
    /**
     * Creates a default stream metadata object and merges in the
     * supplied metadata.
     */
    public IIOMetadata convertStreamMetadata(IIOMetadata inData,
                                             ImageWriteParam param) {
        if (inData == null) {
            throw new IllegalArgumentException("inData == null!");
        }
        
        IIOMetadata sm = getDefaultStreamMetadata(param);
        
        convertMetadata(STREAM_METADATA_NAME, inData, sm);
        
        return sm;
    }
    
    /**
     * Creates a default image metadata object and merges in the
     * supplied metadata.
     */
    public IIOMetadata convertImageMetadata(IIOMetadata inData,
                                            ImageTypeSpecifier imageType,
                                            ImageWriteParam param) {
        if (inData == null) {
            throw new IllegalArgumentException("inData == null!");