com.fmsware.gif
Class GifDecoder

java.lang.Object
  com.fmsware.gif.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++) {
       Image 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.

Version:

1.01 July 2001

Author:

Kevin Weiner, FM Software; LZW decoder adapted from John Cristy's ImageMagick.

Field Summary

protected int[]	act
protected int	bgColor
protected int	bgIndex
protected byte[]	block
protected int	blockSize
protected int	delay
protected int	dispose
protected int	frameCount
protected java.util.Vector	frames
protected int[]	gct
protected boolean	gctFlag
protected int	gctSize
protected int	height
protected int	ih
protected int[]	image
protected java.io.BufferedInputStream	in
protected boolean	interlace
protected int	iw
protected int	ix
protected int	iy
protected int	lastBgColor
protected int	lastDispose
protected int[]	lastImage
protected java.awt.Rectangle	lastRect
protected int[]	lct
protected boolean	lctFlag
protected int	lctSize
protected int	loopCount
protected static int	MaxStackSize
protected int	pixelAspect
protected byte[]	pixels
protected byte[]	pixelStack
protected short[]	prefix
protected int	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
protected int	transIndex
protected boolean	transparency
protected int	width

Constructor Summary

GifDecoder()

Method Summary

protected void	decodeImageData() Decodes LZW image data into pixel array.
static int	encodeColor(java.awt.Color c)
static int	encodeColor(int r, int g, int b)
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	getFrame(int n) Gets the image contents of frame n.
int	getFrameCount() Gets the number of frames read from file.
java.awt.Image	getImage() Gets the first (or only) image read.
int	getLoopCount() Gets the "Netscape" iteration count, if any.
protected int[]	getPixels() Creates new frame image from current data (and previous frames as specified by their disposition codes).
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.lang.String name) Reads GIF file from specified source (file or URL string)
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	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

status

protected int status

width

protected int width

height

protected int height

gctFlag

protected boolean gctFlag

gctSize

protected int gctSize

loopCount

protected int loopCount

gct

protected int[] gct

lct

protected int[] lct

act

protected int[] act

bgIndex

protected int bgIndex

bgColor

protected int bgColor

lastBgColor

protected int lastBgColor

pixelAspect

protected int pixelAspect

lctFlag

protected boolean lctFlag

interlace

protected boolean interlace

lctSize

protected int lctSize

ix

protected int ix

iy

protected int iy

iw

protected int iw

ih

protected int ih

lastRect

protected java.awt.Rectangle lastRect

image

protected int[] image

lastImage

protected int[] lastImage

block

protected byte[] block

blockSize

protected int blockSize

dispose

protected int dispose

lastDispose

protected int lastDispose

transparency

protected boolean transparency

delay

protected int delay

transIndex

protected int transIndex

MaxStackSize

protected static final int MaxStackSize

See Also:

Constant Field Values

prefix

protected short[] prefix

suffix

protected byte[] suffix

pixelStack

protected byte[] pixelStack

pixels

protected byte[] pixels

frames

protected java.util.Vector frames

frameCount

protected int frameCount

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

getFrame

public java.awt.Image getFrame(int n)

Gets the image contents of frame n.

Returns:

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

getFrameCount

public int getFrameCount()

Gets the number of frames read from file.

Returns:

frame count

getImage

public java.awt.Image getImage()

Gets the first (or only) image read.

Returns:

Image 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.

read

public int read(java.io.BufferedInputStream is)

Reads GIF image from stream

Parameters:

is - containing GIF file.

Returns:

read status code (0 = no errors)

read

public int read(java.lang.String name)

Reads GIF file from specified source (file or URL string)

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

init

protected void init()

Initializes or re-initializes reader

read

protected int read()

Reads a single byte from the input stream.

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

resetFrame

protected void resetFrame()

Resets frame state for reading next image.

getPixels

protected int[] getPixels()

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

encodeColor

public static int encodeColor(java.awt.Color c)

encodeColor

public static int encodeColor(int r,
                              int g,
                              int b)

skip

protected void skip()

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