使用Java来处理GIF图片

 一个2个类，一个是读图片的类GifDecoder，一个是写图片的类AnimatedGifEncoder

使用还是挺方便的，下面举个栗子

    public static void main(String[] args) throws IOException {
		GifDecoder decoder = new GifDecoder();
		int status = decoder.read("C:\\Users\\Administrator\\Desktop\\bigImage\\07.gif");
		if (status != GifDecoder.STATUS_OK) {
			throw new IOException("read image error!");
		}
		AnimatedGifEncoder e = new AnimatedGifEncoder();
        //保存的目标图片
		e.start("C:\\Users\\Administrator\\Desktop\\bigImage\\cc.gif");
		e.setRepeat(decoder.getLoopCount());
		e.setDelay(decoder.getDelay(0));
		for (int i = 0; i < decoder.getFrameCount(); i++) {
			BufferedImage image = decoder.getFrame(i);
			//可以加入对图片的处理，比如缩放，压缩质量
			e.addFrame(image);
		}
		e.finish();
	}

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class GifDecoder {

	/**
	 * File read status: No errors.
	 */
	public static final int STATUS_OK = 0;

	/**
	 * File read status: Error decoding file (may be partially decoded)
	 */
	public static final int STATUS_FORMAT_ERROR = 1;

	/**
	 * File read status: Unable to open source.
	 */
	public static final int STATUS_OPEN_ERROR = 2;

	protected BufferedInputStream in;

	protected int status;

	protected int width; // full image width

	protected int height; // full image height

	protected boolean gctFlag; // global color table used

	protected int gctSize; // size of global color table

	protected int loopCount = 1; // iterations; 0 = repeat forever

	protected int[] gct; // global color table

	protected int[] lct; // local color table

	protected int[] act; // active color table

	protected int bgIndex; // background color index

	protected int bgColor; // background color

	protected int lastBgColor; // previous bg color

	protected int pixelAspect; // pixel aspect ratio

	protected boolean lctFlag; // local color table flag

	protected boolean interlace; // interlace flag

	protected int lctSize; // local color table size

	protected int ix, iy, iw, ih; // current image rectangle

	protected Rectangle lastRect; // last image rect

	protected BufferedImage image; // current frame

	protected BufferedImage lastImage; // previous frame

	protected byte[] block = new byte[256]; // current data block

	protected int blockSize = 0; // block size
	// last graphic control extension info

	protected int dispose = 0;

	// 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev
	protected int lastDispose = 0;

	protected boolean transparency = false; // use transparent color

	protected int delay = 0; // delay in milliseconds

	protected int transIndex; // transparent color index

	protected static final int MaxStackSize = 4096;

	// max decoder pixel stack size
	// LZW decoder working arrays
	protected short[] prefix;

	protected byte[] suffix;

	protected byte[] pixelStack;

	protected byte[] pixels;

	protected ArrayList<GifFrame> frames; // frames read from current file

	protected int frameCount;

	static class GifFrame {

		public GifFrame(BufferedImage im, int del) {
			image = im;
			delay = del;
		}

		public BufferedImage image;

		public int delay;
	}

	/**
	 * Gets display duration for specified frame.
	 *
	 * @param n int index of frame
	 * @return delay in milliseconds
	 */
	public int getDelay(int n) {
		//
		delay = -1;
		if ((n >= 0) && (n < frameCount)) {
			delay = ((GifFrame) frames.get(n)).delay;
		}
		return delay;
	}

	/**
	 * Gets the number of frames read from file.
	 * 
	 * @return frame count
	 */
	public int getFrameCount() {
		return frameCount;
	}

	/**
	 * Gets the first (or only) image read.
	 *
	 * @return BufferedImage containing first frame, or null if none.
	 */
	public BufferedImage getImage() {
		return getFrame(0);
	}

	/**
	 * Gets the "Netscape" iteration count, if any. A count of 0 means repeat indefinitiely.
	 *
	 * @return iteration count if one was specified, else 1.
	 */
	public int getLoopCount() {
		return loopCount;
	}

	/**
	 * Creates new frame image from current data (and previous frames as specified by their disposition codes).
	 */
	protected void setPixels() {
		// expose destination image's pixels as int array
		int[] dest = ((DataBufferInt) image.getRaster().getDataBuffer()).getData();
		// fill in starting image contents based on last image's dispose code
		if (lastDispose > 0) {
			if (lastDispose == 3) {
				// use image before last
				int n = frameCount - 2;
				if (n > 0) {
					lastImage = getFrame(n - 1);
				} else {
					lastImage = null;
				}
			}
			if (lastImage != null) {
				int[] prev = ((DataBufferInt) lastImage.getRaster().getDataBuffer()).getData();
				System.arraycopy(prev, 0, dest, 0, width * height);
				// copy pixels
				if (lastDispose == 2) {
					// fill last image rect area with background color
					Graphics2D g = image.createGraphics();
					Color c = null;
					if (transparency) {
						c = new Color(0, 0, 0, 0); // assume background is transparent
					} else {
						c = new Color(lastBgColor); // use given background color
					}
					g.setColor(c);
					g.setComposite(AlphaComposite.Src); // replace area
					g.fill(lastRect);
					g.dispose();
				}
			}
		}
		// copy each source line to the appropriate place in the destination
		int pass = 1;
		int inc = 8;
		int iline = 0;
		for (int i = 0; i < ih; i++) {
			int line = i;
			if (interlace) {
				if (iline >= ih) {
					pass++;
					switch (pass) {
					case 2:
						iline = 4;
						break;
					case 3:
						iline = 2;
						inc = 4;
						break;
					case 4:
						iline = 1;
						inc = 2;
					}
				}
				line = iline;
				iline += inc;
			}
			line += iy;
			if (line < height) {
				int k = line * width;
				int dx = k + ix; // start of line in dest
				int dlim = dx + iw; // end of dest line
				if ((k + width) < dlim) {
					dlim = k + width; // past dest edge
				}
				int sx = i * iw; // start of line in source
				while (dx < dlim) {
					// map color and insert in destination
					int index = ((int) pixels[sx++]) & 0xff;
					int c = act[index];
					if (c != 0) {
						dest[dx] = c;
					}
					dx++;
				}
			}
		}
	}

	/**
	 * Gets the image contents of frame n.
	 *
	 * @return BufferedImage representation of frame, or null if n is invalid.
	 */
	public BufferedImage getFrame(int n) {
		BufferedImage im = null;
		if ((n >= 0) && (n < frameCount)) {
			im = ((GifFrame) frames.get(n)).image;
		}
		return im;
	}

	/**
	 * Gets the image contents
	 *
	 * @return BufferedImage representation of frame, or null if n is invalid.
	 */
	public List<BufferedImage> getFrames() {
		List<BufferedImage> bms = new ArrayList<BufferedImage>();
		for (GifFrame frame : this.frames) {
			bms.add(frame.image);
		}
		return bms;
	}

	/**
	 * Gets image size.
	 *
	 * @return GIF image dimensions
	 */
	public Dimension getFrameSize() {
		return new Dimension(width, height);
	}

	/**
	 * Reads GIF image from stream
	 *
	 * @param BufferedInputStream containing GIF file.
	 * @return read status code (0 = no errors)
	 */
	public int read(BufferedInputStream is) {
		init();
		if (is != null) {
			in = is;
			readHeader();
			if (!err()) {
				readContents();
				if (frameCount < 0) {
					status = STATUS_FORMAT_ERROR;
				}
			}
		} else {
			status = STATUS_OPEN_ERROR;
		}
		try {
			is.close();
		} catch (IOException e) {
		}
		return status;
	}

	/**
	 * Reads GIF image from stream
	 *
	 * @param InputStream containing GIF file.
	 * @return read status code (0 = no errors)
	 */
	public int read(InputStream is) {
		init();
		if (is != null) {
			if (!(is instanceof BufferedInputStream))
				is = new BufferedInputStream(is);
			in = (BufferedInputStream) is;
			readHeader();
			if (!err()) {
				readContents();
				if (frameCount < 0) {
					status = STATUS_FORMAT_ERROR;
				}
			}
		} else {
			status = STATUS_OPEN_ERROR;
		}
		try {
			is.close();
		} catch (IOException e) {
		}
		return status;
	}

	/**
	 * Reads GIF file from specified file/URL source (URL assumed if name contains ":/" or "file:")
	 *
	 * @param name String containing source
	 * @return read status code (0 = no errors)
	 */
	public int read(String name) {
		status = STATUS_OK;
		try {
			name = name.trim().toLowerCase();
			if ((name.indexOf("file:") >= 0) || (name.indexOf(":/") > 0)) {
				URL url = new URL(name);
				in = new BufferedInputStream(url.openStream());
			} else {
				in = new BufferedInputStream(new FileInputStream(name));
			}
			status = read(in);
		} catch (IOException e) {
			status = STATUS_OPEN_ERROR;
		}
		return status;
	}

	/**
	 * Decodes LZW image data into pixel array. Adapted from John Cristy's ImageMagick.
	 */
	protected void decodeImageData() {
		int NullCode = -1;
		int npix = iw * ih;
		int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits, code, count, i, datum, data_size, first,
				top, bi, pi;
		if ((pixels == null) || (pixels.length < npix)) {
			pixels = new byte[npix]; // allocate new pixel array
		}
		if (prefix == null)
			prefix = new short[MaxStackSize];
		if (suffix == null)
			suffix = new byte[MaxStackSize];
		if (pixelStack == null)
			pixelStack = new byte[MaxStackSize + 1];
		// Initialize GIF data stream decoder.
		data_size = read();
		clear = 1 << data_size;
		end_of_information = clear + 1;
		available = clear + 2;
		old_code = NullCode;
		code_size = data_size + 1;
		code_mask = (1 << code_size) - 1;
		for (code = 0; code < clear; code++) {
			prefix[code] = 0;
			suffix[code] = (byte) code;
		}
		// Decode GIF pixel stream.
		datum = bits = count = first = top = pi = bi = 0;
		for (i = 0; i < npix;) {
			if (top == 0) {
				if (bits < code_size) {
					// Load bytes until there are enough bits for a code.
					if (count == 0) {
						// Read a new data block.
						count = readBlock();
						if (count <= 0)
							break;
						bi = 0;
					}
					datum += (((int) block[bi]) & 0xff) << bits;
					bits += 8;
					bi++;
					count--;
					continue;
				}
				// Get the next code.
				code = datum & code_mask;
				datum >>= code_size;
				bits -= code_size;
				// Interpret the code
				if ((code > available) || (code == end_of_information))
					break;
				if (code == clear) {
					// Reset decoder.
					code_size = data_size + 1;
					code_mask = (1 << code_size) - 1;
					available = clear + 2;
					old_code = NullCode;
					continue;
				}
				if (old_code == NullCode) {
					pixelStack[top++] = suffix[code];
					old_code = code;
					first = code;
					continue;
				}
				in_code = code;
				if (code == available) {
					pixelStack[top++] = (byte) first;
					code = old_code;
				}
				while (code > clear) {
					pixelStack[top++] = suffix[code];
					code = prefix[code];
				}
				first = ((int) suffix[code]) & 0xff;
				// Add a new string to the string table,
				if (available >= MaxStackSize)
					break;
				pixelStack[top++] = (byte) first;
				prefix[available] = (short) old_code;
				suffix[available] = (byte) first;
				available++;
				if (((available & code_mask) == 0) && (available < MaxStackSize)) {
					code_size++;
					code_mask += available;
				}
				old_code = in_code;
			}
			// Pop a pixel off the pixel stack.
			top--;
			pixels[pi++] = pixelStack[top];
			i++;
		}
		for (i = pi; i < npix; i++) {
			pixels[i] = 0; // clear missing pixels
		}
	}

	/**
	 * Returns true if an error was encountered during reading/decoding
	 */
	protected boolean err() {
		return status != STATUS_OK;
	}

	/**
	 * Initializes or re-initializes reader
	 */
	protected void init() {
		status = STATUS_OK;
		frameCount = 0;
		frames = new ArrayList<GifFrame>();
		gct = null;
		lct = null;
	}

	/**
	 * Reads a single byte from the input stream.
	 */
	protected int read() {
		int curByte = 0;
		try {
			curByte = in.read();
		} catch (IOException e) {
			status = STATUS_FORMAT_ERROR;
		}
		return curByte;
	}

	/**
	 * Reads next variable length block from input.
	 *
	 * @return number of bytes stored in "buffer"
	 */
	protected int readBlock() {
		blockSize = read();
		int n = 0;
		if (blockSize > 0) {
			try {
				int count = 0;
				while (n < blockSize) {
					count = in.read(block, n, blockSize - n);
					if (count == -1)
						break;
					n += count;
				}
			} catch (IOException e) {
			}
			if (n < blockSize) {
				status = STATUS_FORMAT_ERROR;
			}
		}
		return n;
	}

	/**
	 * Reads color table as 256 RGB integer values
	 *
	 * @param ncolors int number of colors to read
	 * @return int array containing 256 colors (packed ARGB with full alpha)
	 */
	protected int[] readColorTable(int ncolors) {
		int nbytes = 3 * ncolors;
		int[] tab = null;
		byte[] c = new byte[nbytes];
		int n = 0;
		try {
			n = in.read(c);
		} catch (IOException e) {
		}
		if (n < nbytes) {
			status = STATUS_FORMAT_ERROR;
		} else {
			tab = new int[256]; // max size to avoid bounds checks
			int i = 0;
			int j = 0;
			while (i < ncolors) {
				int r = ((int) c[j++]) & 0xff;
				int g = ((int) c[j++]) & 0xff;
				int b = ((int) c[j++]) & 0xff;
				tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
			}
		}
		return tab;
	}

	/**
	 * Main file parser. Reads GIF content blocks.
	 */
	protected void readContents() {
		// read GIF file content blocks
		boolean done = false;
		while (!(done || err())) {
			int code = read();
			switch (code) {
			case 0x2C: // image separator
				readImage();
				break;
			case 0x21: // extension
				code = read();
				switch (code) {
				case 0xf9: // graphics control extension
					readGraphicControlExt();
					break;
				case 0xff: // application extension
					readBlock();
					String app = "";
					for (int i = 0; i < 11; i++) {
						app += (char) block[i];
					}
					if (app.equals("NETSCAPE2.0")) {
						readNetscapeExt();
					} else
						skip(); // don't care
					break;
				default: // uninteresting extension
					skip();
				}
				break;
			case 0x3b: // terminator
				done = true;
				break;
			case 0x00: // bad byte, but keep going and see what happens
				break;
			default:
				status = STATUS_FORMAT_ERROR;
			}
		}
	}

	/**
	 * Reads Graphics Control Extension values
	 */
	protected void readGraphicControlExt() {
		read(); // block size
		int packed = read(); // packed fields
		dispose = (packed & 0x1c) >> 2; // disposal method
		if (dispose == 0) {
			dispose = 1; // elect to keep old image if discretionary
		}
		transparency = (packed & 1) != 0;
		delay = readShort() * 10; // delay in milliseconds
		transIndex = read(); // transparent color index
		read(); // block terminator
	}

	/**
	 * Reads GIF file header information.
	 */
	protected void readHeader() {
		String id = "";
		for (int i = 0; i < 6; i++) {
			id += (char) read();
		}
		if (!id.startsWith("GIF")) {
			status = STATUS_FORMAT_ERROR;
			return;
		}
		readLSD();
		if (gctFlag && !err()) {
			gct = readColorTable(gctSize);
			bgColor = gct[bgIndex];
		}
	}

	/**
	 * Reads next frame image
	 */
	protected void readImage() {
		ix = readShort(); // (sub)image position & size
		iy = readShort();
		iw = readShort();
		ih = readShort();
		int packed = read();
		lctFlag = (packed & 0x80) != 0; // 1 - local color table flag
		interlace = (packed & 0x40) != 0; // 2 - interlace flag
		// 3 - sort flag
		// 4-5 - reserved
		lctSize = 2 << (packed & 7); // 6-8 - local color table size
		if (lctFlag) {
			lct = readColorTable(lctSize); // read table
			act = lct; // make local table active
		} else {
			act = gct; // make global table active
			if (bgIndex == transIndex)
				bgColor = 0;
		}
		int save = 0;
		if (transparency) {
			save = act[transIndex];
			act[transIndex] = 0; // set transparent color if specified
		}
		if (act == null) {
			status = STATUS_FORMAT_ERROR; // no color table defined
		}
		if (err())
			return;
		decodeImageData(); // decode pixel data
		skip();
		if (err())
			return;
		frameCount++;
		// create new image to receive frame data
		image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB_PRE);
		setPixels(); // transfer pixel data to image
		frames.add(new GifFrame(image, delay)); // add image to frame list
		if (transparency) {
			act[transIndex] = save;
		}
		resetFrame();
	}

	/**
	 * Reads Logical Screen Descriptor
	 */
	protected void readLSD() {
		// logical screen size
		width = readShort();
		height = readShort();
		// packed fields
		int packed = read();
		gctFlag = (packed & 0x80) != 0; // 1 : global color table flag
		// 2-4 : color resolution
		// 5 : gct sort flag
		gctSize = 2 << (packed & 7); // 6-8 : gct size
		bgIndex = read(); // background color index
		pixelAspect = read(); // pixel aspect ratio
	}

	/**
	 * Reads Netscape extenstion to obtain iteration count
	 */
	protected void readNetscapeExt() {
		do {
			readBlock();
			if (block[0] == 1) {
				// loop count sub-block
				int b1 = ((int) block[1]) & 0xff;
				int b2 = ((int) block[2]) & 0xff;
				loopCount = (b2 << 8) | b1;
			}
		} while ((blockSize > 0) && !err());
	}

	/**
	 * Reads next 16-bit value, LSB first
	 */
	protected int readShort() {
		// read 16-bit value, LSB first
		return read() | (read() << 8);
	}

	/**
	 * Resets frame state for reading next image.
	 */
	protected void resetFrame() {
		lastDispose = dispose;
		lastRect = new Rectangle(ix, iy, iw, ih);
		lastImage = image;
		lastBgColor = bgColor;
		// int dispose = 0;
		// boolean transparency = false;
		// int delay = 0;
		lct = null;
	}

	protected void skip() {
		do {
			readBlock();
		} while ((blockSize > 0) && !err());
	}
}

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * Class AnimatedGifEncoder - Encodes a GIF file consisting of one or more frames.
 * 
 * <pre>
 *  Example:
 *     AnimatedGifEncoder e = new AnimatedGifEncoder();
 *     e.start(outputFileName);
 *     e.setDelay(1000);   // 1 frame per sec
 *     e.addFrame(image1);
 *     e.addFrame(image2);
 *     e.finish();
 * </pre>
 * 
 * No copyright asserted on the source code of this class. May be used for any purpose, however, refer to the Unisys LZW patent for
 * restrictions on use of the associated LZWEncoder class. Please forward any corrections to [e-mail].
 * 
 * @author Kevin Weiner, FM Software
 * @version 1.03 November 2003
 * 
 */
public class AnimatedGifEncoder {

	protected int width; // image size

	protected int height;

	protected Color transparent = null; // transparent color if given

	protected int transIndex; // transparent index in color table

	protected int repeat = -1; // no repeat

	protected int delay = 0; // frame delay (hundredths)

	protected boolean started = false; // ready to output frames

	protected OutputStream out;

	protected BufferedImage image; // current frame

	protected byte[] pixels; // BGR byte array from frame

	protected byte[] indexedPixels; // converted frame indexed to palette

	protected int colorDepth; // number of bit planes

	protected byte[] colorTab; // RGB palette

	protected boolean[] usedEntry = new boolean[256]; // active palette entries

	protected int palSize = 7; // color table size (bits-1)

	protected int dispose = -1; // disposal code (-1 = use default)

	protected boolean closeStream = false; // close stream when finished

	protected boolean firstFrame = true;

	protected boolean sizeSet = false; // if false, get size from first frame

	protected int sample = 10; // default sample interval for quantizer

	/**
	 * Sets the delay time between each frame, or changes it for subsequent frames (applies to last frame added).
	 * 
	 * @param ms int delay time in milliseconds
	 */
	public void setDelay(int ms) {
		delay = Math.round(ms / 10.0f);
	}

	/**
	 * Sets the GIF frame disposal code for the last added frame and any subsequent frames. Default is 0 if no transparent color has been
	 * set, otherwise 2.
	 * 
	 * @param code int disposal code.
	 */
	public void setDispose(int code) {
		if (code >= 0) {
			dispose = code;
		}
	}

	/**
	 * Sets the number of times the set of GIF frames should be played. Default is 1; 0 means play indefinitely. Must be invoked before the
	 * first image is added.
	 * 
	 * @param iter int number of iterations.
	 * @return
	 */
	public void setRepeat(int iter) {
		if (iter >= 0) {
			repeat = iter;
		}
	}

	/**
	 * Sets the transparent color for the last added frame and any subsequent frames. Since all colors are subject to modification in the
	 * quantization process, the color in the final palette for each frame closest to the given color becomes the transparent color for that
	 * frame. May be set to null to indicate no transparent color.
	 * 
	 * @param c Color to be treated as transparent on display.
	 */
	public void setTransparent(Color c) {
		transparent = c;
	}

	/**
	 * Adds next GIF frame. The frame is not written immediately, but is actually deferred until the next frame is received so that timing
	 * data can be inserted. Invoking <code>finish()</code> flushes all frames. If <code>setSize</code> was not invoked, the size of the
	 * first image is used for all subsequent frames.
	 * 
	 * @param im BufferedImage containing frame to write.
	 * @return true if successful.
	 */
	public boolean addFrame(BufferedImage im) {
		if ((im == null) || !started) {
			return false;
		}
		boolean ok = true;
		try {
			if (!sizeSet) {
				// use first frame's size
				setSize(im.getWidth(), im.getHeight());
			}
			image = im;
			getImagePixels(); // convert to correct format if necessary
			analyzePixels(); // build color table & map pixels
			if (firstFrame) {
				writeLSD(); // logical screen descriptior
				writePalette(); // global color table
				if (repeat >= 0) {
					// use NS app extension to indicate reps
					writeNetscapeExt();
				}
			}
			writeGraphicCtrlExt(); // write graphic control extension
			writeImageDesc(); // image descriptor
			if (!firstFrame) {
				writePalette(); // local color table
			}
			writePixels(); // encode and write pixel data
			firstFrame = false;
		} catch (IOException e) {
			ok = false;
		}

		return ok;
	}

	/**
	 * Flushes any pending data and closes output file. If writing to an OutputStream, the stream is not closed.
	 */
	public boolean finish() {
		if (!started)
			return false;
		boolean ok = true;
		started = false;
		try {
			out.write(0x3b); // gif trailer
			out.flush();
			if (closeStream) {
				out.close();
			}
		} catch (IOException e) {
			ok = false;
		}

		// reset for subsequent use
		transIndex = 0;
		out = null;
		image = null;
		pixels = null;
		indexedPixels = null;
		colorTab = null;
		closeStream = false;
		firstFrame = true;

		return ok;
	}

	/**
	 * Sets frame rate in frames per second. Equivalent to <code>setDelay(1000/fps)</code>.
	 * 
	 * @param fps float frame rate (frames per second)
	 */
	public void setFrameRate(float fps) {
		if (fps != 0f) {
			delay = Math.round(100f / fps);
		}
	}

	/**
	 * Sets quality of color quantization (conversion of images to the maximum 256 colors allowed by the GIF specification). Lower values
	 * (minimum = 1) produce better colors, but slow processing significantly. 10 is the default, and produces good color mapping at
	 * reasonable speeds. Values greater than 20 do not yield significant improvements in speed.
	 * 
	 * @param quality int greater than 0.
	 * @return
	 */
	public void setQuality(int quality) {
		if (quality < 1)
			quality = 1;
		sample = quality;
	}

	/**
	 * Sets the GIF frame size. The default size is the size of the first frame added if this method is not invoked.
	 * 
	 * @param w int frame width.
	 * @param h int frame width.
	 */
	public void setSize(int w, int h) {
		if (started && !firstFrame)
			return;
		width = w;
		height = h;
		if (width < 1)
			width = 320;
		if (height < 1)
			height = 240;
		sizeSet = true;
	}

	/**
	 * Initiates GIF file creation on the given stream. The stream is not closed automatically.
	 * 
	 * @param os OutputStream on which GIF images are written.
	 * @return false if initial write failed.
	 */
	public boolean start(OutputStream os) {
		if (os == null)
			return false;
		boolean ok = true;
		closeStream = false;
		out = os;
		try {
			writeString("GIF89a"); // header
		} catch (IOException e) {
			ok = false;
		}
		return started = ok;
	}

	/**
	 * Initiates writing of a GIF file with the specified name.
	 * 
	 * @param file String containing output file name.
	 * @return false if open or initial write failed.
	 */
	public boolean start(String file) {
		boolean ok = true;
		try {
			out = new BufferedOutputStream(new FileOutputStream(file));
			ok = start(out);
			closeStream = true;
		} catch (IOException e) {
			ok = false;
		}
		return started = ok;
	}

	/**
	 * Analyzes image colors and creates color map.
	 */
	protected void analyzePixels() {
		int len = pixels.length;
		int nPix = len / 3;
		indexedPixels = new byte[nPix];
		NeuQuant nq = new NeuQuant(pixels, len, sample);
		// initialize quantizer
		colorTab = nq.process(); // create reduced palette
		// convert map from BGR to RGB
		for (int i = 0; i < colorTab.length; i += 3) {
			byte temp = colorTab[i];
			colorTab[i] = colorTab[i + 2];
			colorTab[i + 2] = temp;
			usedEntry[i / 3] = false;
		}
		// map image pixels to new palette
		int k = 0;
		for (int i = 0; i < nPix; i++) {
			int index = nq.map(pixels[k++] & 0xff, pixels[k++] & 0xff, pixels[k++] & 0xff);
			usedEntry[index] = true;
			indexedPixels[i] = (byte) index;
		}
		pixels = null;
		colorDepth = 8;
		palSize = 7;
		// get closest match to transparent color if specified
		if (transparent != null) {
			transIndex = findClosest(transparent);
		}
	}

	/**
	 * Returns index of palette color closest to c
	 * 
	 */
	protected int findClosest(Color c) {
		if (colorTab == null)
			return -1;
		int r = c.getRed();
		int g = c.getGreen();
		int b = c.getBlue();
		int minpos = 0;
		int dmin = 256 * 256 * 256;
		int len = colorTab.length;
		for (int i = 0; i < len;) {
			int dr = r - (colorTab[i++] & 0xff);
			int dg = g - (colorTab[i++] & 0xff);
			int db = b - (colorTab[i] & 0xff);
			int d = dr * dr + dg * dg + db * db;
			int index = i / 3;
			if (usedEntry[index] && (d < dmin)) {
				dmin = d;
				minpos = index;
			}
			i++;
		}
		return minpos;
	}

	/**
	 * Extracts image pixels into byte array "pixels"
	 */
	protected void getImagePixels() {
		int w = image.getWidth();
		int h = image.getHeight();
		int type = image.getType();
		if ((w != width) || (h != height) || (type != BufferedImage.TYPE_3BYTE_BGR)) {
			// create new image with right size/format
			BufferedImage temp = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR);
			Graphics2D g = temp.createGraphics();
			g.drawImage(image, 0, 0, null);
			image = temp;
		}
		pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
	}

	/**
	 * Writes Graphic Control Extension
	 */
	protected void writeGraphicCtrlExt() throws IOException {
		out.write(0x21); // extension introducer
		out.write(0xf9); // GCE label
		out.write(4); // data block size
		int transp, disp;
		if (transparent == null) {
			transp = 0;
			disp = 0; // dispose = no action
		} else {
			transp = 1;
			disp = 2; // force clear if using transparent color
		}
		if (dispose >= 0) {
			disp = dispose & 7; // user override
		}
		disp <<= 2;

		// packed fields
		out.write(0 | // 1:3 reserved
				disp | // 4:6 disposal
				0 | // 7 user input - 0 = none
				transp); // 8 transparency flag

		writeShort(delay); // delay x 1/100 sec
		out.write(transIndex); // transparent color index
		out.write(0); // block terminator
	}

	/**
	 * Writes Image Descriptor
	 */
	protected void writeImageDesc() throws IOException {
		out.write(0x2c); // image separator
		writeShort(0); // image position x,y = 0,0
		writeShort(0);
		writeShort(width); // image size
		writeShort(height);
		// packed fields
		if (firstFrame) {
			// no LCT - GCT is used for first (or only) frame
			out.write(0);
		} else {
			// specify normal LCT
			out.write(0x80 | // 1 local color table 1=yes
					0 | // 2 interlace - 0=no
					0 | // 3 sorted - 0=no
					0 | // 4-5 reserved
					palSize); // 6-8 size of color table
		}
	}

	/**
	 * Writes Logical Screen Descriptor
	 */
	protected void writeLSD() throws IOException {
		// logical screen size
		writeShort(width);
		writeShort(height);
		// packed fields
		out.write((0x80 | // 1 : global color table flag = 1 (gct used)
				0x70 | // 2-4 : color resolution = 7
				0x00 | // 5 : gct sort flag = 0
				palSize)); // 6-8 : gct size

		out.write(0); // background color index
		out.write(0); // pixel aspect ratio - assume 1:1
	}

	/**
	 * Writes Netscape application extension to define repeat count.
	 */
	protected void writeNetscapeExt() throws IOException {
		out.write(0x21); // extension introducer
		out.write(0xff); // app extension label
		out.write(11); // block size
		writeString("NETSCAPE" + "2.0"); // app id + auth code
		out.write(3); // sub-block size
		out.write(1); // loop sub-block id
		writeShort(repeat); // loop count (extra iterations, 0=repeat forever)
		out.write(0); // block terminator
	}

	/**
	 * Writes color table
	 */
	protected void writePalette() throws IOException {
		out.write(colorTab, 0, colorTab.length);
		int n = (3 * 256) - colorTab.length;
		for (int i = 0; i < n; i++) {
			out.write(0);
		}
	}

	/**
	 * Encodes and writes pixel data
	 */
	protected void writePixels() throws IOException {
		LZWEncoder encoder = new LZWEncoder(width, height, indexedPixels, colorDepth);
		encoder.encode(out);
	}

	/**
	 * Write 16-bit value to output stream, LSB first
	 */
	protected void writeShort(int value) throws IOException {
		out.write(value & 0xff);
		out.write((value >> 8) & 0xff);
	}

	/**
	 * Writes string to output stream
	 */
	protected void writeString(String s) throws IOException {
		for (int i = 0; i < s.length(); i++) {
			out.write((byte) s.charAt(i));
		}
	}
}

/*
 * NeuQuant Neural-Net Quantization Algorithm ------------------------------------------
 * 
 * Copyright (c) 1994 Anthony Dekker
 * 
 * NEUQUANT Neural-Net quantization algorithm by Anthony Dekker, 1994. See "Kohonen neural networks for optimal colour quantization" in
 * "Network: Computation in Neural Systems" Vol. 5 (1994) pp 351-367. for a discussion of the algorithm.
 * 
 * Any party obtaining a copy of these files from the author, directly or indirectly, is granted, free of charge, a full and unrestricted
 * irrevocable, world-wide, paid up, royalty-free, nonexclusive right and license to deal in this software and documentation files (the
 * "Software"), including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons who receive copies from any such party to do so, with the only requirement being that this copyright
 * notice remain intact.
 */

// Ported to Java 12/00 K Weiner
class NeuQuant {

	protected static final int netsize = 256; /* number of colours used */

	/* four primes near 500 - assume no image has a length so large */
	/* that it is divisible by all four primes */
	protected static final int prime1 = 499;

	protected static final int prime2 = 491;

	protected static final int prime3 = 487;

	protected static final int prime4 = 503;

	protected static final int minpicturebytes = (3 * prime4);

	/* minimum size for input image */

	/*
	 * Program Skeleton ---------------- [select samplefac in range 1..30] [read image from input file] pic = (unsigned char*)
	 * malloc(3*width*height); initnet(pic,3*width*height,samplefac); learn(); unbiasnet(); [write output image header, using
	 * writecolourmap(f)] inxbuild(); write output image using inxsearch(b,g,r)
	 */

	/*
	 * Network Definitions -------------------
	 */

	protected static final int maxnetpos = (netsize - 1);

	protected static final int netbiasshift = 4; /* bias for colour values */

	protected static final int ncycles = 100; /* no. of learning cycles */

	/* defs for freq and bias */
	protected static final int intbiasshift = 16; /* bias for fractions */

	protected static final int intbias = (((int) 1) << intbiasshift);

	protected static final int gammashift = 10; /* gamma = 1024 */

	protected static final int gamma = (((int) 1) << gammashift);

	protected static final int betashift = 10;

	protected static final int beta = (intbias >> betashift); /* beta = 1/1024 */

	protected static final int betagamma = (intbias << (gammashift - betashift));

	/* defs for decreasing radius factor */
	protected static final int initrad = (netsize >> 3); /*
															 * for 256 cols, radius starts
															 */

	protected static final int radiusbiasshift = 6; /* at 32.0 biased by 6 bits */

	protected static final int radiusbias = (((int) 1) << radiusbiasshift);

	protected static final int initradius = (initrad * radiusbias); /*
																	 * and decreases by a
																	 */

	protected static final int radiusdec = 30; /* factor of 1/30 each cycle */

	/* defs for decreasing alpha factor */
	protected static final int alphabiasshift = 10; /* alpha starts at 1.0 */

	protected static final int initalpha = (((int) 1) << alphabiasshift);

	protected int alphadec; /* biased by 10 bits */

	/* radbias and alpharadbias used for radpower calculation */
	protected static final int radbiasshift = 8;

	protected static final int radbias = (((int) 1) << radbiasshift);

	protected static final int alpharadbshift = (alphabiasshift + radbiasshift);

	protected static final int alpharadbias = (((int) 1) << alpharadbshift);

	/*
	 * Types and Global Variables --------------------------
	 */

	protected byte[] thepicture; /* the input image itself */

	protected int lengthcount; /* lengthcount = H*W*3 */

	protected int samplefac; /* sampling factor 1..30 */

	// typedef int pixel[4]; /* BGRc */
	protected int[][] network; /* the network itself - [netsize][4] */

	protected int[] netindex = new int[256];

	/* for network lookup - really 256 */

	protected int[] bias = new int[netsize];

	/* bias and freq arrays for learning */
	protected int[] freq = new int[netsize];

	protected int[] radpower = new int[initrad];

	/* radpower for precomputation */

	/*
	 * Initialise network in range (0,0,0) to (255,255,255) and set parameters
	 * -----------------------------------------------------------------------
	 */
	public NeuQuant(byte[] thepic, int len, int sample) {

		int i;
		int[] p;

		thepicture = thepic;
		lengthcount = len;
		samplefac = sample;

		network = new int[netsize][];
		for (i = 0; i < netsize; i++) {
			network[i] = new int[4];
			p = network[i];
			p[0] = p[1] = p[2] = (i << (netbiasshift + 8)) / netsize;
			freq[i] = intbias / netsize; /* 1/netsize */
			bias[i] = 0;
		}
	}

	public byte[] colorMap() {
		byte[] map = new byte[3 * netsize];
		int[] index = new int[netsize];
		for (int i = 0; i < netsize; i++)
			index[network[i][3]] = i;
		int k = 0;
		for (int i = 0; i < netsize; i++) {
			int j = index[i];
			map[k++] = (byte) (network[j][0]);
			map[k++] = (byte) (network[j][1]);
			map[k++] = (byte) (network[j][2]);
		}
		return map;
	}

	/*
	 * Insertion sort of network and building of netindex[0..255] (to do after unbias)
	 * -------------------------------------------------------------------------------
	 */
	public void inxbuild() {

		int i, j, smallpos, smallval;
		int[] p;
		int[] q;
		int previouscol, startpos;

		previouscol = 0;
		startpos = 0;
		for (i = 0; i < netsize; i++) {
			p = network[i];
			smallpos = i;
			smallval = p[1]; /* index on g */
			/* find smallest in i..netsize-1 */
			for (j = i + 1; j < netsize; j++) {
				q = network[j];
				if (q[1] < smallval) { /* index on g */
					smallpos = j;
					smallval = q[1]; /* index on g */
				}
			}
			q = network[smallpos];
			/* swap p (i) and q (smallpos) entries */
			if (i != smallpos) {
				j = q[0];
				q[0] = p[0];
				p[0] = j;
				j = q[1];
				q[1] = p[1];
				p[1] = j;
				j = q[2];
				q[2] = p[2];
				p[2] = j;
				j = q[3];
				q[3] = p[3];
				p[3] = j;
			}
			/* smallval entry is now in position i */
			if (smallval != previouscol) {
				netindex[previouscol] = (startpos + i) >> 1;
				for (j = previouscol + 1; j < smallval; j++)
					netindex[j] = i;
				previouscol = smallval;
				startpos = i;
			}
		}
		netindex[previouscol] = (startpos + maxnetpos) >> 1;
		for (j = previouscol + 1; j < 256; j++)
			netindex[j] = maxnetpos; /* really 256 */
	}

	/*
	 * Main Learning Loop ------------------
	 */
	public void learn() {

		int i, j, b, g, r;
		int radius, rad, alpha, step, delta, samplepixels;
		byte[] p;
		int pix, lim;

		if (lengthcount < minpicturebytes)
			samplefac = 1;
		alphadec = 30 + ((samplefac - 1) / 3);
		p = thepicture;
		pix = 0;
		lim = lengthcount;
		samplepixels = lengthcount / (3 * samplefac);
		delta = samplepixels / ncycles;
		alpha = initalpha;
		radius = initradius;

		rad = radius >> radiusbiasshift;
		if (rad <= 1)
			rad = 0;
		for (i = 0; i < rad; i++)
			radpower[i] = alpha * (((rad * rad - i * i) * radbias) / (rad * rad));

		// fprintf(stderr,"beginning 1D learning: initial radius=%d\n", rad);

		if (lengthcount < minpicturebytes)
			step = 3;
		else if ((lengthcount % prime1) != 0)
			step = 3 * prime1;
		else {
			if ((lengthcount % prime2) != 0)
				step = 3 * prime2;
			else {
				if ((lengthcount % prime3) != 0)
					step = 3 * prime3;
				else
					step = 3 * prime4;
			}
		}

		i = 0;
		while (i < samplepixels) {
			b = (p[pix + 0] & 0xff) << netbiasshift;
			g = (p[pix + 1] & 0xff) << netbiasshift;
			r = (p[pix + 2] & 0xff) << netbiasshift;
			j = contest(b, g, r);

			altersingle(alpha, j, b, g, r);
			if (rad != 0)
				alterneigh(rad, j, b, g, r); /* alter neighbours */

			pix += step;
			if (pix >= lim)
				pix -= lengthcount;

			i++;
			if (delta == 0)
				delta = 1;
			if (i % delta == 0) {
				alpha -= alpha / alphadec;
				radius -= radius / radiusdec;
				rad = radius >> radiusbiasshift;
				if (rad <= 1)
					rad = 0;
				for (j = 0; j < rad; j++)
					radpower[j] = alpha * (((rad * rad - j * j) * radbias) / (rad * rad));
			}
		}
		// fprintf(stderr,"finished 1D learning: final alpha=%f
		// !\n",((float)alpha)/initalpha);
	}

	/*
	 * Search for BGR values 0..255 (after net is unbiased) and return colour index
	 * ----------------------------------------------------------------------------
	 */
	public int map(int b, int g, int r) {

		int i, j, dist, a, bestd;
		int[] p;
		int best;

		bestd = 1000; /* biggest possible dist is 256*3 */
		best = -1;
		i = netindex[g]; /* index on g */
		j = i - 1; /* start at netindex[g] and work outwards */

		while ((i < netsize) || (j >= 0)) {
			if (i < netsize) {
				p = network[i];
				dist = p[1] - g; /* inx key */
				if (dist >= bestd)
					i = netsize; /* stop iter */
				else {
					i++;
					if (dist < 0)
						dist = -dist;
					a = p[0] - b;
					if (a < 0)
						a = -a;
					dist += a;
					if (dist < bestd) {
						a = p[2] - r;
						if (a < 0)
							a = -a;
						dist += a;
						if (dist < bestd) {
							bestd = dist;
							best = p[3];
						}
					}
				}
			}
			if (j >= 0) {
				p = network[j];
				dist = g - p[1]; /* inx key - reverse dif */
				if (dist >= bestd)
					j = -1; /* stop iter */
				else {
					j--;
					if (dist < 0)
						dist = -dist;
					a = p[0] - b;
					if (a < 0)
						a = -a;
					dist += a;
					if (dist < bestd) {
						a = p[2] - r;
						if (a < 0)
							a = -a;
						dist += a;
						if (dist < bestd) {
							bestd = dist;
							best = p[3];
						}
					}
				}
			}
		}
		return (best);
	}

	public byte[] process() {
		learn();
		unbiasnet();
		inxbuild();
		return colorMap();
	}

	/*
	 * Unbias network to give byte values 0..255 and record position i to prepare for sort
	 * -----------------------------------------------------------------------------------
	 */
	public void unbiasnet() {

		int i;

		for (i = 0; i < netsize; i++) {
			network[i][0] >>= netbiasshift;
			network[i][1] >>= netbiasshift;
			network[i][2] >>= netbiasshift;
			network[i][3] = i; /* record colour no */
		}
	}

	/*
	 * Move adjacent neurons by precomputed alpha*(1-((i-j)^2/[r]^2)) in radpower[|i-j|]
	 * ---------------------------------------------------------------------------------
	 */
	protected void alterneigh(int rad, int i, int b, int g, int r) {

		int j, k, lo, hi, a, m;
		int[] p;

		lo = i - rad;
		if (lo < -1)
			lo = -1;
		hi = i + rad;
		if (hi > netsize)
			hi = netsize;

		j = i + 1;
		k = i - 1;
		m = 1;
		while ((j < hi) || (k > lo)) {
			a = radpower[m++];
			if (j < hi) {
				p = network[j++];
				try {
					p[0] -= (a * (p[0] - b)) / alpharadbias;
					p[1] -= (a * (p[1] - g)) / alpharadbias;
					p[2] -= (a * (p[2] - r)) / alpharadbias;
				} catch (Exception e) {
				} // prevents 1.3 miscompilation
			}
			if (k > lo) {
				p = network[k--];
				try {
					p[0] -= (a * (p[0] - b)) / alpharadbias;
					p[1] -= (a * (p[1] - g)) / alpharadbias;
					p[2] -= (a * (p[2] - r)) / alpharadbias;
				} catch (Exception e) {
				}
			}
		}
	}

	/*
	 * Move neuron i towards biased (b,g,r) by factor alpha ----------------------------------------------------
	 */
	protected void altersingle(int alpha, int i, int b, int g, int r) {

		/* alter hit neuron */
		int[] n = network[i];
		n[0] -= (alpha * (n[0] - b)) / initalpha;
		n[1] -= (alpha * (n[1] - g)) / initalpha;
		n[2] -= (alpha * (n[2] - r)) / initalpha;
	}

	/*
	 * Search for biased BGR values ----------------------------
	 */
	protected int contest(int b, int g, int r) {

		/* finds closest neuron (min dist) and updates freq */
		/* finds best neuron (min dist-bias) and returns position */
		/* for frequently chosen neurons, freq[i] is high and bias[i] is negative */
		/* bias[i] = gamma*((1/netsize)-freq[i]) */

		int i, dist, a, biasdist, betafreq;
		int bestpos, bestbiaspos, bestd, bestbiasd;
		int[] n;

		bestd = ~(((int) 1) << 31);
		bestbiasd = bestd;
		bestpos = -1;
		bestbiaspos = bestpos;

		for (i = 0; i < netsize; i++) {
			n = network[i];
			dist = n[0] - b;
			if (dist < 0)
				dist = -dist;
			a = n[1] - g;
			if (a < 0)
				a = -a;
			dist += a;
			a = n[2] - r;
			if (a < 0)
				a = -a;
			dist += a;
			if (dist < bestd) {
				bestd = dist;
				bestpos = i;
			}
			biasdist = dist - ((bias[i]) >> (intbiasshift - netbiasshift));
			if (biasdist < bestbiasd) {
				bestbiasd = biasdist;
				bestbiaspos = i;
			}
			betafreq = (freq[i] >> betashift);
			freq[i] -= betafreq;
			bias[i] += (betafreq << gammashift);
		}
		freq[bestpos] += beta;
		bias[bestpos] -= betagamma;
		return (bestbiaspos);
	}
}

// ==============================================================================
// Adapted from Jef Poskanzer's Java port by way of J. M. G. Elliott.
// K Weiner 12/00

class LZWEncoder {

	private static final int EOF = -1;

	private int imgW, imgH;

	private byte[] pixAry;

	private int initCodeSize;

	private int remaining;

	private int curPixel;

	// GIFCOMPR.C - GIF Image compression routines
	//
	// Lempel-Ziv compression based on 'compress'. GIF modifications by
	// David Rowley ([e-mail])

	// General DEFINEs

	static final int BITS = 12;

	static final int HSIZE = 5003; // 80% occupancy

	// GIF Image compression - modified 'compress'
	//
	// Based on: compress.c - File compression ala IEEE Computer, June 1984.
	//
	// By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
	// Jim McKie (decvax!mcvax!jim)
	// Steve Davies (decvax!vax135!petsd!peora!srd)
	// Ken Turkowski (decvax!decwrl!turtlevax!ken)
	// James A. Woods (decvax!ihnp4!ames!jaw)
	// Joe Orost (decvax!vax135!petsd!joe)

	int n_bits; // number of bits/code

	int maxbits = BITS; // user settable max # bits/code

	int maxcode; // maximum code, given n_bits

	int maxmaxcode = 1 << BITS; // should NEVER generate this code

	int[] htab = new int[HSIZE];

	int[] codetab = new int[HSIZE];

	int hsize = HSIZE; // for dynamic table sizing

	int free_ent = 0; // first unused entry

	// block compression parameters -- after all codes are used up,
	// and compression rate changes, start over.
	boolean clear_flg = false;

	// Algorithm: use open addressing double hashing (no chaining) on the
	// prefix code / next character combination. We do a variant of Knuth's
	// algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
	// secondary probe. Here, the modular division first probe is gives way
	// to a faster exclusive-or manipulation. Also do block compression with
	// an adaptive reset, whereby the code table is cleared when the compression
	// ratio decreases, but after the table fills. The variable-length output
	// codes are re-sized at this point, and a special CLEAR code is generated
	// for the decompressor. Late addition: construct the table according to
	// file size for noticeable speed improvement on small files. Please direct
	// questions about this implementation to ames!jaw.

	int g_init_bits;

	int ClearCode;

	int EOFCode;

	// output
	//
	// Output the given code.
	// Inputs:
	// code: A n_bits-bit integer. If == -1, then EOF. This assumes
	// that n_bits =< wordsize - 1.
	// Outputs:
	// Outputs code to the file.
	// Assumptions:
	// Chars are 8 bits long.
	// Algorithm:
	// Maintain a BITS character long buffer (so that 8 codes will
	// fit in it exactly). Use the VAX insv instruction to insert each
	// code in turn. When the buffer fills up empty it and start over.

	int cur_accum = 0;

	int cur_bits = 0;

	int masks[] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF,
			0x7FFF, 0xFFFF };

	// Number of characters so far in this 'packet'
	int a_count;

	// Define the storage for the packet accumulator
	byte[] accum = new byte[256];

	// ----------------------------------------------------------------------------
	LZWEncoder(int width, int height, byte[] pixels, int color_depth) {
		imgW = width;
		imgH = height;
		pixAry = pixels;
		initCodeSize = Math.max(2, color_depth);
	}

	// Add a character to the end of the current packet, and if it is 254
	// characters, flush the packet to disk.
	void char_out(byte c, OutputStream outs) throws IOException {
		accum[a_count++] = c;
		if (a_count >= 254)
			flush_char(outs);
	}

	// Clear out the hash table

	// table clear for block compress
	void cl_block(OutputStream outs) throws IOException {
		cl_hash(hsize);
		free_ent = ClearCode + 2;
		clear_flg = true;

		output(ClearCode, outs);
	}

	// reset code table
	void cl_hash(int hsize) {
		for (int i = 0; i < hsize; ++i)
			htab[i] = -1;
	}

	void compress(int init_bits, OutputStream outs) throws IOException {
		int fcode;
		int i /* = 0 */;
		int c;
		int ent;
		int disp;
		int hsize_reg;
		int hshift;

		// Set up the globals: g_init_bits - initial number of bits
		g_init_bits = init_bits;

		// Set up the necessary values
		clear_flg = false;
		n_bits = g_init_bits;
		maxcode = MAXCODE(n_bits);

		ClearCode = 1 << (init_bits - 1);
		EOFCode = ClearCode + 1;
		free_ent = ClearCode + 2;

		a_count = 0; // clear packet

		ent = nextPixel();

		hshift = 0;
		for (fcode = hsize; fcode < 65536; fcode *= 2)
			++hshift;
		hshift = 8 - hshift; // set hash code range bound

		hsize_reg = hsize;
		cl_hash(hsize_reg); // clear hash table

		output(ClearCode, outs);

		outer_loop: while ((c = nextPixel()) != EOF) {
			fcode = (c << maxbits) + ent;
			i = (c << hshift) ^ ent; // xor hashing

			if (htab[i] == fcode) {
				ent = codetab[i];
				continue;
			} else if (htab[i] >= 0) // non-empty slot
			{
				disp = hsize_reg - i; // secondary hash (after G. Knott)
				if (i == 0)
					disp = 1;
				do {
					if ((i -= disp) < 0)
						i += hsize_reg;

					if (htab[i] == fcode) {
						ent = codetab[i];
						continue outer_loop;
					}
				} while (htab[i] >= 0);
			}
			output(ent, outs);
			ent = c;
			if (free_ent < maxmaxcode) {
				codetab[i] = free_ent++; // code -> hashtable
				htab[i] = fcode;
			} else
				cl_block(outs);
		}
		// Put out the final code.
		output(ent, outs);
		output(EOFCode, outs);
	}

	// ----------------------------------------------------------------------------
	void encode(OutputStream os) throws IOException {
		os.write(initCodeSize); // write "initial code size" byte

		remaining = imgW * imgH; // reset navigation variables
		curPixel = 0;

		compress(initCodeSize + 1, os); // compress and write the pixel data

		os.write(0); // write block terminator
	}

	// Flush the packet to disk, and reset the accumulator
	void flush_char(OutputStream outs) throws IOException {
		if (a_count > 0) {
			outs.write(a_count);
			outs.write(accum, 0, a_count);
			a_count = 0;
		}
	}

	final int MAXCODE(int n_bits) {
		return (1 << n_bits) - 1;
	}

	// ----------------------------------------------------------------------------
	// Return the next pixel from the image
	// ----------------------------------------------------------------------------
	private int nextPixel() {
		if (remaining == 0)
			return EOF;

		--remaining;

		byte pix = pixAry[curPixel++];

		return pix & 0xff;
	}

	void output(int code, OutputStream outs) throws IOException {
		cur_accum &= masks[cur_bits];

		if (cur_bits > 0)
			cur_accum |= (code << cur_bits);
		else
			cur_accum = code;

		cur_bits += n_bits;

		while (cur_bits >= 8) {
			char_out((byte) (cur_accum & 0xff), outs);
			cur_accum >>= 8;
			cur_bits -= 8;
		}

		// If the next entry is going to be too big for the code size,
		// then increase it, if possible.
		if (free_ent > maxcode || clear_flg) {
			if (clear_flg) {
				maxcode = MAXCODE(n_bits = g_init_bits);
				clear_flg = false;
			} else {
				++n_bits;
				if (n_bits == maxbits)
					maxcode = maxmaxcode;
				else
					maxcode = MAXCODE(n_bits);
			}
		}

		if (code == EOFCode) {
			// At EOF, write the rest of the buffer.
			while (cur_bits > 0) {
				char_out((byte) (cur_accum & 0xff), outs);
				cur_accum >>= 8;
				cur_bits -= 8;
			}

			flush_char(outs);
		}
	}
}

 

转载于:https://my.oschina.net/u/1261213/blog/736569