GifEncoder.java源程序

/*
 * @(#)GIFEncoder.java    0.90 4/21/96 Adam Doppelt
 */
import java.io.*;
import java.awt.*;
import java.awt.image.*;

/**
 * GIFEncoder is a class which takes an image and saves it to a stream
 * using the GIF file format (<A
 * HREF="http://www.dcs.ed.ac.uk/%7Emxr/gfx/">Graphics Interchange
 * Format</A>). A GIFEncoder
 * is constructed with either an AWT Image (which must be fully
 * loaded) or a set of RGB arrays. The image can be written out with a
 * call to <CODE>Write</CODE>.<P>
 *
 * Three caveats:
 * <UL>
 *   <LI>GIFEncoder will convert the image to indexed color upon
 *   construction. This will take some time, depending on the size of
 *   the image. Also, actually writing the image out (Write) will take
 *   time.<P>
 *
 *   <LI>The image cannot have more than 256 colors, since GIF is an 8
 *   bit format. For a 24 bit to 8 bit quantization algorithm, see
 *   Graphics Gems II III.2 by Xialoin Wu. Or check out his <A
 *   HREF="http://www.csd.uwo.ca/faculty/wu/cq.c">C source</A>.<P>
 *
 *   <LI>Since the image must be completely loaded into memory,
 *   GIFEncoder may have problems with large images. Attempting to
 *   encode an image which will not fit into memory will probably
 *   result in the following exception:<P>
 *   <CODE>java.awt.AWTException: Grabber returned false: 192</CODE><P>
 * </UL><P>
 *
 * GIFEncoder is based upon gifsave.c, which was written and released
 * by:<P>
 * <CENTER>
 *                                  Sverre H. Huseby<BR>
 *                                   Bjoelsengt. 17<BR>
 *                                     N-0468 Oslo<BR>
 *                                       Norway<P>
 *
 *                                 Phone: +47 2 230539<BR>
 *                                 [email protected]<P>
 * </CENTER>
 * @version 0.90 21 Apr 1996
 * @author <A HREF="http://www.cs.brown.edu/people/amd/">Adam Doppelt</A> */
public class GIFEncoder {
    short width_, height_;
    int numColors_;
    byte pixels_[], colors_[];
   
    ScreenDescriptor sd_;
    ImageDescriptor id_;
   
/**
 * Construct a GIFEncoder. The constructor will convert the image to
 * an indexed color array. <B>This may take some time.</B><P>
 *
 * @param image The image to encode. The image <B>must</B> be
 * completely loaded.
 * @exception AWTException Will be thrown if the pixel grab fails. This
 * can happen if Java runs out of memory. It may also indicate that the image
 * contains more than 256 colors.
 * */
    public GIFEncoder(Image image) throws AWTException {
 width_ = (short)image.getWidth(null);
 height_ = (short)image.getHeight(null);

 int values[] = new int[width_ * height_];
 PixelGrabber grabber = new PixelGrabber(
     image, 0, 0, width_, height_, values, 0, width_);
 
 try {
     if(grabber.grabPixels() != true)
  throw new AWTException("Grabber returned false: " +
           grabber.status());
 }
 catch (InterruptedException e) { ; }
 
 byte r[][] = new byte[width_][height_];
 byte g[][] = new byte[width_][height_];
 byte b[][] = new byte[width_][height_];
 int index = 0;
 for (int y = 0; y < height_; ++y)
     for (int x = 0; x < width_; ++x) {
  r[x][y] = (byte)((values[index] >> 16) & 0xFF);
  g[x][y] = (byte)((values[index] >> 8) & 0xFF);
  b[x][y] = (byte)((values[index]) & 0xFF); 
  ++index;
     }
 ToIndexedColor(r, g, b);
    }

/**
 * Construct a GIFEncoder. The constructor will convert the image to
 * an indexed color array. <B>This may take some time.</B><P>
 *
 * Each array stores intensity values for the image. In other words,
 * r[x][y] refers to the red intensity of the pixel at column x, row
 * y.<P>
 *
 * @param r An array containing the red intensity values.
 * @param g An array containing the green intensity values.
 * @param b An array containing the blue intensity values.
 *
 * @exception AWTException Will be thrown if the image contains more than
 * 256 colors.
 * */
    public GIFEncoder(byte r[][], byte g[][], byte b[][]) throws AWTException {
 width_ = (short)(r.length);
 height_ = (short)(r[0].length);

 ToIndexedColor(r, g, b);
    }

/**
 * Writes the image out to a stream in the GIF file format. This will
 * be a single GIF87a image, non-interlaced, with no background color.
 * <B>This may take some time.</B><P>
 *
 * @param output The stream to output to. This should probably be a
 * buffered stream.
 *
 * @exception IOException Will be thrown if a write operation fails.
 * */
    public void Write(OutputStream output) throws IOException {
 BitUtils.WriteString(output, "GIF87a");
 
 ScreenDescriptor sd = new ScreenDescriptor(width_, height_,
         numColors_);
 sd.Write(output);

 output.write(colors_, 0, colors_.length);

 ImageDescriptor id = new ImageDescriptor(width_, height_, ',');
 id.Write(output);

 byte codesize = BitUtils.BitsNeeded(numColors_);
 if (codesize == 1)
     ++codesize;
 output.write(codesize);

 LZWCompressor.LZWCompress(output, codesize, pixels_);
 output.write(0);

 id = new ImageDescriptor((byte)0, (byte)0, ';');
 id.Write(output);
 output.flush();
    }

    void ToIndexedColor(byte r[][], byte g[][],
   byte b[][]) throws AWTException {
 pixels_ = new byte[width_ * height_];
 colors_ = new byte[256 * 3];
 int colornum = 0;
 for (int x = 0; x < width_; ++x) {
     for (int y = 0; y < height_; ++y) {
  int search;
  for (search = 0; search < colornum; ++search)
      if (colors_[search * 3]     == r[x][y] &&
   colors_[search * 3 + 1] == g[x][y] &&
   colors_[search * 3 + 2] == b[x][y])
   break;
  
  if (search > 255)
      throw new AWTException("Too many colors.");

  pixels_[y * width_ + x] = (byte)search;
  
  if (search == colornum) {
      colors_[search * 3]     = r[x][y];
      colors_[search * 3 + 1] = g[x][y];
      colors_[search * 3 + 2] = b[x][y];
      ++colornum;
  }
     }
 }
 numColors_ = 1 << BitUtils.BitsNeeded(colornum);
 byte copy[] = new byte[numColors_ * 3];
 System.arraycopy(colors_, 0, copy, 0, numColors_ * 3);
 colors_ = copy;
    }
   
}

class BitFile {
    OutputStream output_;
    byte buffer_[];
    int index_, bitsLeft_;

    public BitFile(OutputStream output) {
 output_ = output;
 buffer_ = new byte[256];
 index_ = 0;
 bitsLeft_ = 8;
    }

    public void Flush() throws IOException {
 int numBytes = index_ + (bitsLeft_ == 8 ? 0 : 1);
 if (numBytes > 0) {
     output_.write(numBytes);
     output_.write(buffer_, 0, numBytes);
     buffer_[0] = 0;
     index_ = 0;
     bitsLeft_ = 8;
 }
    }

    public void WriteBits(int bits, int numbits) throws IOException {
 int bitsWritten = 0;
 int numBytes = 255;
 do {
     if ((index_ == 254 && bitsLeft_ == 0) || index_ > 254) {
  output_.write(numBytes);
  output_.write(buffer_, 0, numBytes);

  buffer_[0] = 0;
  index_ = 0;
  bitsLeft_ = 8;
     }

     if (numbits <= bitsLeft_) {
  buffer_[index_] |= (bits & ((1 << numbits) - 1)) <<
      (8 - bitsLeft_);
  bitsWritten += numbits;
  bitsLeft_ -= numbits;
  numbits = 0;
     }
     else {
  buffer_[index_] |= (bits & ((1 << bitsLeft_) - 1)) <<
      (8 - bitsLeft_);
  bitsWritten += bitsLeft_;
  bits >>= bitsLeft_;
  numbits -= bitsLeft_;
  buffer_[++index_] = 0;
  bitsLeft_ = 8;
     }
 } while (numbits != 0);
    }
}

class LZWStringTable {
    private final static int RES_CODES = 2;
    private final static short HASH_FREE = (short)0xFFFF;
    private final static short NEXT_FIRST = (short)0xFFFF;
    private final static int MAXBITS = 12;
    private final static int MAXSTR = (1 << MAXBITS);
    private final static short HASHSIZE = 9973;
    private final static short HASHSTEP = 2039;

    byte strChr_[];
    short strNxt_[];
    short strHsh_[];
    short numStrings_;

    public LZWStringTable() {
 strChr_ = new byte[MAXSTR];
 strNxt_ = new short[MAXSTR];
 strHsh_ = new short[HASHSIZE];   
    }

    public int AddCharString(short index, byte b) {
 int hshidx;

 if (numStrings_ >= MAXSTR)
     return 0xFFFF;
 
 hshidx = Hash(index, b);
 while (strHsh_[hshidx] != HASH_FREE)
     hshidx = (hshidx + HASHSTEP) % HASHSIZE;
 
 strHsh_[hshidx] = numStrings_;
 strChr_[numStrings_] = b;
 strNxt_[numStrings_] = (index != HASH_FREE) ? index : NEXT_FIRST;

 return numStrings_++;
    }
   
    public short FindCharString(short index, byte b) {
 int hshidx, nxtidx;

 if (index == HASH_FREE)
     return b;

 hshidx = Hash(index, b);
 while ((nxtidx = strHsh_[hshidx]) != HASH_FREE) {
     if (strNxt_[nxtidx] == index && strChr_[nxtidx] == b)
  return (short)nxtidx;
     hshidx = (hshidx + HASHSTEP) % HASHSIZE;
 }

 return (short)0xFFFF;
    }

    public void ClearTable(int codesize) {
 numStrings_ = 0;
 
 for (int q = 0; q < HASHSIZE; q++) {
     strHsh_[q] = HASH_FREE;
 }

 int w = (1 << codesize) + RES_CODES;
 for (int q = 0; q < w; q++)
     AddCharString((short)0xFFFF, (byte)q);
    }
   
    static public int Hash(short index, byte lastbyte) {
 return ((int)((short)(lastbyte << 8) ^ index) & 0xFFFF) % HASHSIZE;
    }
}

class LZWCompressor {

    public static void LZWCompress(OutputStream output, int codesize,
       byte toCompress[]) throws IOException {
 byte c;
 short index;
 int clearcode, endofinfo, numbits, limit, errcode;
 short prefix = (short)0xFFFF;

 BitFile bitFile = new BitFile(output);
 LZWStringTable strings = new LZWStringTable();

 clearcode = 1 << codesize;
 endofinfo = clearcode + 1;
   
 numbits = codesize + 1;
 limit = (1 << numbits) - 1;
 
 strings.ClearTable(codesize);
 bitFile.WriteBits(clearcode, numbits);

 for (int loop = 0; loop < toCompress.length; ++loop) {
     c = toCompress[loop];
     if ((index = strings.FindCharString(prefix, c)) != -1)
  prefix = index;
     else {
  bitFile.WriteBits(prefix, numbits);
  if (strings.AddCharString(prefix, c) > limit) {
      if (++numbits > 12) {
   bitFile.WriteBits(clearcode, numbits - 1);
   strings.ClearTable(codesize);
   numbits = codesize + 1;
      }
      limit = (1 << numbits) - 1;
  }
  
  prefix = (short)((short)c & 0xFF);
     }
 }
 
 if (prefix != -1)
     bitFile.WriteBits(prefix, numbits);
 
 bitFile.WriteBits(endofinfo, numbits);
 bitFile.Flush();
    }
}

class ScreenDescriptor {
    public short localScreenWidth_, localScreenHeight_;
    private byte byte_;
    public byte backgroundColorIndex_, pixelAspectRatio_;

    public ScreenDescriptor(short width, short height, int numColors) {
 localScreenWidth_ = width;
 localScreenHeight_ = height;
 SetGlobalColorTableSize((byte)(BitUtils.BitsNeeded(numColors) - 1));
 SetGlobalColorTableFlag((byte)1);
 SetSortFlag((byte)0);
 SetColorResolution((byte)7);
 backgroundColorIndex_ = 0;
 pixelAspectRatio_ = 0;
    }

    public void Write(OutputStream output) throws IOException {
 BitUtils.WriteWord(output, localScreenWidth_);
 BitUtils.WriteWord(output, localScreenHeight_);
 output.write(byte_);
 output.write(backgroundColorIndex_);
 output.write(pixelAspectRatio_);
    }

    public void SetGlobalColorTableSize(byte num) {
 byte_ |= (num & 7);
    }

    public void SetSortFlag(byte num) {
 byte_ |= (num & 1) << 3;
    }

    public void SetColorResolution(byte num) {
 byte_ |= (num & 7) << 4;
    }
   
    public void SetGlobalColorTableFlag(byte num) {
 byte_ |= (num & 1) << 7;
    }
}

class ImageDescriptor {
    public byte separator_;
    public short leftPosition_, topPosition_, width_, height_;
    private byte byte_;

    public ImageDescriptor(short width, short height, char separator) {
 separator_ = (byte)separator;
 leftPosition_ = 0;
 topPosition_ = 0;
 width_ = width;
 height_ = height;
 SetLocalColorTableSize((byte)0);
 SetReserved((byte)0);
 SetSortFlag((byte)0);
 SetInterlaceFlag((byte)0);
 SetLocalColorTableFlag((byte)0);
    }
   
    public void Write(OutputStream output) throws IOException {
 output.write(separator_);
 BitUtils.WriteWord(output, leftPosition_);
 BitUtils.WriteWord(output, topPosition_);
 BitUtils.WriteWord(output, width_);
 BitUtils.WriteWord(output, height_);  
 output.write(byte_);
    }

    public void SetLocalColorTableSize(byte num) {
 byte_ |= (num & 7);
    }

    public void SetReserved(byte num) {
 byte_ |= (num & 3) << 3;
    }

    public void SetSortFlag(byte num) {
 byte_ |= (num & 1) << 5;
    }
   
    public void SetInterlaceFlag(byte num) {
 byte_ |= (num & 1) << 6;
    }

    public void SetLocalColorTableFlag(byte num) {
 byte_ |= (num & 1) << 7;
    }
}

class BitUtils {
    public static byte BitsNeeded(int n) {
 byte ret = 1;

 if (n-- == 0)
     return 0;

 while ((n >>= 1) != 0)
     ++ret;
 
 return ret;
    }   

    public static void WriteWord(OutputStream output,
     short w) throws IOException {
 output.write(w & 0xFF);
 output.write((w >> 8) & 0xFF);
    }
   
    static void WriteString(OutputStream output,
       String string) throws IOException {
 for (int loop = 0; loop < string.length(); ++loop)
     output.write((byte)(string.charAt(loop)));
    }
}

 

 

来自：http://luohonghong.blog.163.com/blog/static/7831205820095341548326/