Mega Code Archive
GIFEncoder is a class which takes an image and saves it to a stream using the GIF file format
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/*
* @(#)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>
* sverrehu@ifi.uio.no<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)));
}
}
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