GifEncoder.java

package ij.io;
import java.util.*;
import java.io.*;
import java.awt.Image;
import java.awt.image.*;

public class GifEncoder {

    private boolean interlace = false;
    private int width, height;
    private byte[] pixels;
    private byte[] r, g, b; // the color look-up table
    private int pixelIndex;
    private int numPixels;
    private int transparentPixel = -1; // hpm
    
    public GifEncoder(int width, int height, byte[] pixels, byte[] r, byte[] g, byte[] b) {
        this.width = width;
        this.height = height;
        this.pixels = pixels;
        this.r = r; this.g = g; this.b = b;
        interlace = false;
        pixelIndex = 0;
        numPixels = width*height;
    }
    
    public GifEncoder(Image img) {
        width = img.getWidth(null);
        height = img.getHeight(null);
        pixels = new byte[width * height];
        PixelGrabber pg = new PixelGrabber(img, 0, 0, width, height, false);
        try {
            pg.grabPixels();
        } catch (InterruptedException e) {
            System.err.println(e);
        };
        ColorModel cm = pg.getColorModel();
        if (cm instanceof IndexColorModel)
                {
            pixels = (byte[])(pg.getPixels());
                        // hpm
                        IndexColorModel icm = (IndexColorModel)cm;
                        setTransparentPixel(icm.getTransparentPixel());
                }
        else
            throw new IllegalArgumentException("Image must be 8-bit");
        IndexColorModel m = (IndexColorModel)cm;
        int mapSize = m.getMapSize();
        r = new byte[mapSize];
        g = new byte[mapSize];
        b = new byte[mapSize];
        m.getReds(r); 
        m.getGreens(g); 
        m.getBlues(b); 
        interlace = false;
        pixelIndex = 0;
        numPixels = width*height;

    }

    public void write(OutputStream out) throws IOException {
        // Figure out how many bits to use.
        int numColors = r.length;
        int BitsPerPixel;
        if (numColors<=2)
            BitsPerPixel = 1;
        else if (numColors<=4)
            BitsPerPixel = 2;
        else if (numColors<=16)
            BitsPerPixel = 4;
        else
            BitsPerPixel = 8;

        int ColorMapSize = 1 << BitsPerPixel;
        byte[] reds = new byte[ColorMapSize];
        byte[] grns = new byte[ColorMapSize];
        byte[] blus = new byte[ColorMapSize];
        for (int i=0; i<numColors; i++) {
            reds[i] = r[i];
            grns[i] = g[i];
            blus[i] = b[i];
        }

                // hpm
        GIFEncode(out, width, height, interlace, (byte) 0, 
                          getTransparentPixel(), BitsPerPixel, reds, grns, blus);
    }

        // hpm
        public void setTransparentPixel(int pixel) {
            transparentPixel = pixel;
        }

        // hpm
        public int getTransparentPixel() {
            return transparentPixel;
        }

    static void writeString(OutputStream out, String str) throws IOException
        {
        byte[] buf = str.getBytes();
        out.write(buf);
        }

    // Adapted from ppmtogif, which is based on GIFENCOD by David
    // Rowley <mgardi@watdscu.waterloo.edu>.  Lempel-Zim compression
    // based on "compress".

    int Width, Height;
    boolean Interlace;

    void GIFEncode(
    OutputStream outs, int Width, int Height, boolean Interlace, byte Background, int Transparent, int BitsPerPixel, byte[] Red, byte[] Green, byte[] Blue )
    throws IOException
    {
    byte B;
    int LeftOfs, TopOfs;
    int ColorMapSize;
    int InitCodeSize;
    int i;

    this.Width = Width;
    this.Height = Height;
    this.Interlace = Interlace;
    ColorMapSize = 1 << BitsPerPixel;
    LeftOfs = TopOfs = 0;

    // The initial code size
    if ( BitsPerPixel <= 1 )
        InitCodeSize = 2;
    else
        InitCodeSize = BitsPerPixel;

    // Write the Magic header
    writeString( outs, "GIF89a" );

    // Write out the screen width and height
    Putword( Width, outs );
    Putword( Height, outs );

    // Indicate that there is a global colour map
    B = (byte) 0x80;        // Yes, there is a color map
    // OR in the resolution
    B |= (byte) ( ( 8 - 1 ) << 4 );
    // Not sorted
    // OR in the Bits per Pixel
    B |= (byte) ( ( BitsPerPixel - 1 ) );

    // Write it out
    Putbyte( B, outs );

    // Write out the Background colour
    Putbyte( Background, outs );

    // Pixel aspect ratio - 1:1.
    //Putbyte( (byte) 49, outs );
    // Java's GIF reader currently has a bug, if the aspect ratio byte is
    // not zero it throws an ImageFormatException.  It doesn't know that
    // 49 means a 1:1 aspect ratio.  Well, whatever, zero works with all
    // the other decoders I've tried so it probably doesn't hurt.
    Putbyte( (byte) 0, outs );

    // Write out the Global Colour Map
    for ( i = 0; i < ColorMapSize; ++i )
        {
        Putbyte( Red[i], outs );
        Putbyte( Green[i], outs );
        Putbyte( Blue[i], outs );
        }

    // Write out extension for transparent colour index, if necessary.
    if ( Transparent != -1 )
        {
        Putbyte( (byte) '!', outs );
        Putbyte( (byte) 0xf9, outs );
        Putbyte( (byte) 4, outs );
        Putbyte( (byte) 1, outs );
        Putbyte( (byte) 0, outs );
        Putbyte( (byte) 0, outs );
        Putbyte( (byte) Transparent, outs );
        Putbyte( (byte) 0, outs );
        }

    // Write an Image separator
    Putbyte( (byte) ',', outs );

    // Write the Image header
    Putword( LeftOfs, outs );
    Putword( TopOfs, outs );
    Putword( Width, outs );
    Putword( Height, outs );

    // Write out whether or not the image is interlaced
    if ( Interlace )
        Putbyte( (byte) 0x40, outs );
    else
        Putbyte( (byte) 0x00, outs );

    // Write out the initial code size
    Putbyte( (byte) InitCodeSize, outs );

    // Go and actually compress the data
    compress( InitCodeSize+1, outs );

    // Write out a Zero-length packet (to end the series)
    Putbyte( (byte) 0, outs );

    // Write the GIF file terminator
    Putbyte( (byte) ';', outs );
    }


    static final int EOF = -1;

    // Return the next pixel from the image
    int GIFNextPixel() throws IOException {
        if (pixelIndex==numPixels)
            return EOF;
        else
            return ((byte[])pixels)[pixelIndex++] & 0xff;
    }


    // Write out a word to the GIF file
    void Putword( int w, OutputStream outs ) throws IOException
    {
    Putbyte( (byte) ( w & 0xff ), outs );
    Putbyte( (byte) ( ( w >> 8 ) & 0xff ), outs );
    }

    // Write out a byte to the GIF file
    void Putbyte( byte b, OutputStream outs ) throws IOException
    {
    outs.write( b );
    }


    // GIFCOMPR.C       - GIF Image compression routines
    //
    // Lempel-Ziv compression based on 'compress'.  GIF modifications by
    // David Rowley (mgardi@watdcsu.waterloo.edu)

    // 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

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

    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;

    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;

    char_init();

    ent = GIFNextPixel();

    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 = GIFNextPixel()) != 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 );
    }

    // 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 };

    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 );
        }
    }

    // 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;
    }

    // GIF Specific routines

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

    // Set up the 'byte output' routine
    void char_init()
    {
    a_count = 0;
    }

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

    // 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 );
    }

    // 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;
        }
    }

    }

class GifEncoderHashitem {
    public int rgb;
    public int count;
    public int index;
    public boolean isTransparent;

    public GifEncoderHashitem(int rgb, int count, int index, boolean isTransparent) {
        this.rgb = rgb;
        this.count = count;
        this.index = index;
        this.isTransparent = isTransparent;
    }

}