Mega Code Archive
Decodes a GIF file into one or more frames
<![CDATA[
import java.net.*;
import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.image.*;
/**
* Class GifDecoder - Decodes a GIF file into one or more frames.
* <br><pre>
* Example:
* GifDecoder d = new GifDecoder();
* d.read("sample.gif");
* int n = d.getFrameCount();
* for (int i = 0; i < n; i++) {
* BufferedImage frame = d.getFrame(i); // frame i
* int t = d.getDelay(i); // display duration of frame in milliseconds
* // do something with frame
* }
* </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 any additional
* restrictions. Please forward any corrections to kweiner@fmsware.com.
*
* @author Kevin Weiner, FM Software; LZW decoder adapted from John Cristy's ImageMagick.
* @version 1.03 November 2003
*
*/
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 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 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();
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;
dispose = 0;
transparency = false;
delay = 0;
lct = null;
}
/**
* Skips variable length blocks up to and including
* next zero length block.
*/
protected void skip() {
do {
readBlock();
} while ((blockSize > 0) && !err());
}
}
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