Class GifDecoder

java.lang.Object
  GifDecoder

public class GifDecoder
extends java.lang.Object

Class GifDecoder - Decodes a GIF file into one or more frames.

 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
    }
 

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.

Nested Class Summary

(package private) static class

GifDecoder.GifFrame This is a private subclass to represent the frame for the GIF.

Field Summary

protected int[]	act Active color table.
protected int	bgColor Background color.
protected int	bgIndex Background color index.
protected byte[]	block Current data block.
protected int	blockSize Block size.
protected int	delay Delay in milliseconds.
protected int	dispose Last graphic control extension info.
protected int	frameCount Frame Count.
protected java.util.ArrayList	frames Frames read from current file.
protected int[]	gct Global color table.
protected boolean	gctFlag Global color table used.
protected int	gctSize Size of global color table.
protected int	height Full image height.
protected int	ih Current image rectangle.
protected java.awt.image.BufferedImage	image Current frame.
protected java.io.BufferedInputStream	in BufferedInputStream for reading input.
protected boolean	interlace Interlace flag.
protected int	iw Current image rectangle.
protected int	ix Current image rectangle.
protected int	iy Current image rectangle.
protected int	lastBgColor Previous bg color.
protected int	lastDispose 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev.
protected java.awt.image.BufferedImage	lastImage Previous frame.
protected java.awt.Rectangle	lastRect Last image rect.
protected int[]	lct Local color table.
protected boolean	lctFlag Local color table flag.
protected int	lctSize Local color table size.
protected int	loopCount Number of Iterations; 0 = repeat forever.
protected static int	MaxStackSize Max decoder pixel stack size.
protected int	pixelAspect Pixel aspect ratio.
protected byte[]	pixels LZW decoder working array.
protected byte[]	pixelStack LZW decoder working array.
protected short[]	prefix LZW decoder working array.
protected int	status An int representing the status.
static int	STATUS_FORMAT_ERROR File read status: Error decoding file (may be partially decoded).
static int	STATUS_OK File read status: No errors.
static int	STATUS_OPEN_ERROR File read status: Unable to open source.
protected byte[]	suffix LZW decoder working array.
protected int	transIndex Transparent color index.
protected boolean	transparency Use transparent color.
protected int	width Full image width.

Constructor Summary

GifDecoder()

Method Summary

protected void	decodeImageData() Decodes LZW image data into pixel array.
protected boolean	err() Returns true if an error was encountered during reading/decoding.
int	getDelay(int n) Gets display duration for specified frame.
java.awt.image.BufferedImage	getFrame(int n) Gets the image contents of frame n.
int	getFrameCount() Gets the number of frames read from file.
java.awt.Dimension	getFrameSize() Gets image size.
java.awt.image.BufferedImage	getImage() Gets the first (or only) image read.
int	getLoopCount() Gets the "Netscape" iteration count, if any.
protected void	init() Initializes or re-initializes reader.
protected int	read() Reads a single byte from the input stream.
int	read(java.io.BufferedInputStream is) Reads GIF image from stream.
int	read(java.io.InputStream is) Reads GIF image from stream.
int	read(java.lang.String name) Reads GIF file from specified file/URL source (URL assumed if name contains ":/" or "file:").
protected int	readBlock() Reads next variable length block from input.
protected int[]	readColorTable(int ncolors) Reads color table as 256 RGB integer values.
protected void	readContents() Main file parser.
protected void	readGraphicControlExt() Reads Graphics Control Extension values.
protected void	readHeader() Reads GIF file header information.
protected void	readImage() Reads next frame image.
protected void	readLSD() Reads Logical Screen Descriptor.
protected void	readNetscapeExt() Reads Netscape extenstion to obtain iteration count.
protected int	readShort() Reads next 16-bit value, LSB first.
protected void	resetFrame() Resets frame state for reading next image.
protected void	setPixels() Creates new frame image from current data (and previous frames as specified by their disposition codes).
protected void	skip() Skips variable length blocks up to and including next zero length block.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

STATUS_OK

public static final int STATUS_OK

File read status: No errors.

See Also:

Constant Field Values

STATUS_FORMAT_ERROR

public static final int STATUS_FORMAT_ERROR

File read status: Error decoding file (may be partially decoded).

See Also:

Constant Field Values

STATUS_OPEN_ERROR

public static final int STATUS_OPEN_ERROR

File read status: Unable to open source.

See Also:

Constant Field Values

in

protected java.io.BufferedInputStream in

BufferedInputStream for reading input.

status

protected int status

An int representing the status.

width

protected int width

Full image width.

height

protected int height

Full image height.

gctFlag

protected boolean gctFlag

Global color table used.

gctSize

protected int gctSize

Size of global color table.

loopCount

protected int loopCount

Number of Iterations; 0 = repeat forever.

gct

protected int[] gct

Global color table.

lct

protected int[] lct

Local color table.

act

protected int[] act

Active color table.

bgIndex

protected int bgIndex

Background color index.

bgColor

protected int bgColor

Background color.

lastBgColor

protected int lastBgColor

Previous bg color.

pixelAspect

protected int pixelAspect

Pixel aspect ratio.

lctFlag

protected boolean lctFlag

Local color table flag.

interlace

protected boolean interlace

Interlace flag.

lctSize

protected int lctSize

Local color table size.

ix

protected int ix

Current image rectangle.

iy

protected int iy

Current image rectangle.

iw

protected int iw

Current image rectangle.

ih

protected int ih

Current image rectangle.

lastRect

protected java.awt.Rectangle lastRect

Last image rect.

image

protected java.awt.image.BufferedImage image

Current frame.

lastImage

protected java.awt.image.BufferedImage lastImage

Previous frame.

block

protected byte[] block

Current data block.

blockSize

protected int blockSize

Block size.

dispose

protected int dispose

Last graphic control extension info.

lastDispose

protected int lastDispose

0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev.

transparency

protected boolean transparency

Use transparent color.

delay

protected int delay

Delay in milliseconds.

transIndex

protected int transIndex

Transparent color index.

MaxStackSize

protected static final int MaxStackSize

Max decoder pixel stack size.

See Also:

Constant Field Values

prefix

protected short[] prefix

LZW decoder working array.

suffix

protected byte[] suffix

LZW decoder working array.

pixelStack

protected byte[] pixelStack

LZW decoder working array.

pixels

protected byte[] pixels

LZW decoder working array.

frames

protected java.util.ArrayList frames

Frames read from current file.

frameCount

protected int frameCount

Frame Count.

Constructor Detail

GifDecoder

public GifDecoder()

Method Detail

getDelay

public int getDelay(int n)

Gets display duration for specified frame.

Parameters:

n - int index of frame

Returns:

delay in milliseconds

getFrameCount

public int getFrameCount()

Gets the number of frames read from file.

Returns:

frame count

getImage

public java.awt.image.BufferedImage getImage()

Gets the first (or only) image read.

Returns:

BufferedImage containing first frame, or null if none.

getLoopCount

public int getLoopCount()

Gets the "Netscape" iteration count, if any. A count of 0 means repeat indefinitiely.

Returns:

iteration count if one was specified, else 1.

setPixels

protected void setPixels()

Creates new frame image from current data (and previous frames as specified by their disposition codes).

getFrame

public java.awt.image.BufferedImage getFrame(int n)

Gets the image contents of frame n.

Parameters:

n - an int representing the frame number to get

Returns:

BufferedImage representation of frame, or null if n is invalid.

getFrameSize

public java.awt.Dimension getFrameSize()

Gets image size.

Returns:

GIF image dimensions

read

public int read(java.io.BufferedInputStream is)

Reads GIF image from stream.

Parameters:

is - containing GIF file.

Returns:

read BufferedInputStream status code (0 = no errors)

read

public int read(java.io.InputStream is)

Reads GIF image from stream.

Parameters:

is - InputStream containing GIF file.

Returns:

is read status code (0 = no errors)

read

public int read(java.lang.String name)

Reads GIF file from specified file/URL source (URL assumed if name contains ":/" or "file:").

Parameters:

name - String containing source

Returns:

read status code (0 = no errors)

decodeImageData

protected void decodeImageData()

Decodes LZW image data into pixel array. Adapted from John Cristy's ImageMagick.

err

protected boolean err()

Returns true if an error was encountered during reading/decoding.

Returns:

true if status != STATUS_OK, false if status == STATUS_OK

init

protected void init()

Initializes or re-initializes reader.

read

protected int read()

Reads a single byte from the input stream.

Returns:

an int representing the read in byte value

readBlock

protected int readBlock()

Reads next variable length block from input.

Returns:

number of bytes stored in "buffer"

readColorTable

protected int[] readColorTable(int ncolors)

Reads color table as 256 RGB integer values.

Parameters:

ncolors - int number of colors to read

Returns:

int array containing 256 colors (packed ARGB with full alpha)

readContents

protected void readContents()

Main file parser. Reads GIF content blocks.

readGraphicControlExt

protected void readGraphicControlExt()

Reads Graphics Control Extension values.

readHeader

protected void readHeader()

Reads GIF file header information.

readImage

protected void readImage()

Reads next frame image.

readLSD

protected void readLSD()

Reads Logical Screen Descriptor.

readNetscapeExt

protected void readNetscapeExt()

Reads Netscape extenstion to obtain iteration count.

readShort

protected int readShort()

Reads next 16-bit value, LSB first.

Returns:

an int representing a 16-bit value from the input stream

resetFrame

protected void resetFrame()

Resets frame state for reading next image.

skip

protected void skip()

Skips variable length blocks up to and including next zero length block.