寫selenium自動化時，為了檢視執行效果，後給瀏覽器截圖，想到可以生成gif圖片來快速預覽。看到已經有人實現了，直接拿過來。作者是Kevin Weiner。

共涉及到三個java檔案，分別是NeuQuant.java,LZWEncoder.java, AnimatedGifEncoder.java,有了這三個檔案，我們可以自己編寫方法呼叫

，程式碼如下：

        BufferedImage src1 = ImageIO.read(new File("Img221785570.jpg"));
        BufferedImage src2 = ImageIO.read(new File("W.gif"));
        //BufferedImage src3 = ImageIO.read(new File("c:/ship3.jpg")); 
        AnimatedGifEncoder e = new AnimatedGifEncoder(); 
        e.setRepeat(0); 
        e.start("laoma.gif"); 
        e.setDelay(300); // 1 frame per sec 
        e.addFrame(src1); 
        e.setDelay(100); 
        e.addFrame(src2); 
        e.setDelay(100); 
    //  e.addFrame(src2); 
        e.finish(); 
 

三個java檔案原始碼如下：

NeuQuant.java

    public 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, j;
            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);
        }
    }
 

LZWEncoder.java原始碼如下：

    package com.yeetrack.selenium.Image;

    import java.io.OutputStream;
    import java.io.IOException;
    //==============================================================================
    //  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 (
 
[email protected])
        // 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);
            }
        }
    }

AnimatedGifEncoder.java原始碼如下：

    package com.yeetrack.selenium.Image;

    import java.io.*;
    import java.awt.*;
    import java.awt.image.*;

    /**
     * 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 [email protected]
     *
     * @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));
            }
        }
    }