GIF decoding

Question

This works on WinXP but not Linux. Why? It takes the first frame of an animated gif and writes a thumbnail.
            GifDecoder d = new GifDecoder();    
            try {
                fis = new FileInputStream(file);          
                bis = new BufferedInputStream(fis);            
                log.debug("reading gif");
                d.read(bis);
                log.debug("reading framecount");
                int n = d.getFrameCount();
                log.debug("read framecount" + n);
                for (int i = 0; i < 1; i++) {
                    BufferedImage frame = d.getFrame(i);  // frame i
                    int t = d.getDelay(i);  // display duration of frame in milliseconds
                    log.debug("resizing frame");
                        File gifoutputfile = new File("gif" + i + outputthumbFilename);
                    BufferedImage bdest = new BufferedImage(60, 60, BufferedImage.TYPE_INT_RGB);
                    Graphics2D g = bdest.createGraphics();
                    AffineTransform at = AffineTransform.getScaleInstance((double) 60 / frame.getWidth(), (double) 60 / frame.getHeight());
                    g.drawRenderedImage(frame, at);
                    ImageIO.setUseCache(false);
                    ImageIO.write(bdest, "GIF", new File(outputthumbFilename));           
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
* 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 [email protected].
* @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;
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;
int dispose = 0;
boolean transparency = false;
int 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());
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 

Answer 1

Niklas wrote:
This works on WinXP but not Linux. Why? Please don't just post reams of code without providing more context and information.
How is it failing on Linux? Wrong results? What are they? Error messages? What do they say? You need to give us some place to start looking.