com.sun.media.jai.codec
Class PNGDecodeParam

java.lang.Object
  |
  +--com.sun.media.jai.codec.PNGDecodeParam

All Implemented Interfaces:

Cloneable, ImageDecodeParam, Serializable

public class PNGDecodeParam

extends Object

implements ImageDecodeParam

An instance of ImageDecodeParam for decoding images in the PNG format. PNGDecodeParam allows several aspects of the decoding process for PNG images to be controlled. By default, decoding produces output images with the following properties:

Images with a bit depth of 8 or less use a DataBufferByte to hold the pixel data. 16-bit images use a DataBufferUShort.

Palette color images and non-transparent grayscale images with bit depths of 1, 2, or 4 will have a MultiPixelPackedSampleModel and an IndexColorModel. For palette color images, the ColorModel palette contains the red, green, blue, and optionally alpha palette information. For grayscale images, the palette is used to expand the pixel data to cover the range 0-255. The pixels are stored packed 8, 4, or 2 to the byte.

All other images are stored using a PixelInterleavedSampleModel with each sample of a pixel occupying its own byte or short within the DataBuffer. A ComponentColorModel is used which simply extracts the red, green, blue, gray, and/or alpha information from separate DataBuffer entries.

Five aspects of this process may be altered by means of methods in this class.

setSuppressAlpha() prevents an alpha channel from appearing in the output.

setExpandPalette() turns palette-color images into 3-or 4-channel full-color images.

setOutput8BitGray() causes 1, 2, or 4 bit grayscale images to be output in 8-bit form, using a ComponentSampleModel and ComponentColorModel.

setDecodingExponent() causes the output image to be gamma-corrected using a supplied output gamma value.

setExpandGrayAlpha() causes 2-channel gray/alpha (GA) images to be output as full-color (GGGA) images, which may simplify further processing and display.

This class is not a committed part of the JAI API. It may be removed or changed in future releases of JAI.

See Also:

Serialized Form

Constructor Summary

PNGDecodeParam()
Constructs a default instance of PNGDecodeParam.

Method Summary

float	getDisplayExponent() Returns the current value of the display exponent parameter.
PNGEncodeParam	getEncodeParam() If getGenerateEncodeParam() is true, this method may be called after decoding has completed, and will return an instance of PNGEncodeParam containing information about the contents of the PNG file just decoded.
boolean	getExpandGrayAlpha() Returns the current setting of the gray/alpha expansion.
boolean	getExpandPalette() Returns true if palette-color images will be expanded to produce full-color output.
boolean	getGenerateEncodeParam() Returns true if an instance of PNGEncodeParam will be available after an image has been decoded via the getEncodeParam method.
boolean	getOutput8BitGray() Returns the current value of the 8-bit gray output parameter.
boolean	getPerformGammaCorrection() Returns true if gamma correction is to be performed on the image data.
boolean	getSuppressAlpha() Returns true if alpha (transparency) will be prevented from appearing in the output.
float	getUserExponent() Returns the current value of the user exponent parameter.
void	setDisplayExponent(float displayExponent) Sets the display exponent to a given value.
void	setEncodeParam(PNGEncodeParam encodeParam) Sets the current encoder param instance.
void	setExpandGrayAlpha(boolean expandGrayAlpha) If set, images containing one channel of gray and one channel of alpha (GA) will be output in a 4-channel format (GGGA).
void	setExpandPalette(boolean expandPalette) If set, palette color images (PNG color type 3) will be decoded into full-color (RGB) output images.
void	setGenerateEncodeParam(boolean generateEncodeParam) If set, an instance of PNGEncodeParam will be available after an image has been decoded via the getEncodeParam method that encapsulates information about the contents of the PNG file.
void	setOutput8BitGray(boolean output8BitGray) If set, grayscale images with a bit depth less than 8 (1, 2, or 4) will be output in 8 bit form.
void	setPerformGammaCorrection(boolean performGammaCorrection) Turns gamma corection of the image data on or off.
void	setSuppressAlpha(boolean suppressAlpha) If set, no alpha (transparency) channel will appear in the output image.
void	setUserExponent(float userExponent) Sets the user exponent to a given value.

Methods inherited from class java.lang.Object

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

Constructor Detail

PNGDecodeParam

public PNGDecodeParam()

Constructs a default instance of PNGDecodeParam.

Method Detail

getSuppressAlpha

public boolean getSuppressAlpha()

Returns true if alpha (transparency) will be prevented from appearing in the output.

setSuppressAlpha

public void setSuppressAlpha(boolean suppressAlpha)

If set, no alpha (transparency) channel will appear in the output image.

The default is to allow transparency to appear in the output image.

getExpandPalette

public boolean getExpandPalette()

Returns true if palette-color images will be expanded to produce full-color output.

setExpandPalette

public void setExpandPalette(boolean expandPalette)

If set, palette color images (PNG color type 3) will be decoded into full-color (RGB) output images. The output image may have 3 or 4 channels, depending on the presence of transparency information.

The default is to output palette images using a single channel. The palette information is used to construct the output image's ColorModel.

getOutput8BitGray

public boolean getOutput8BitGray()

Returns the current value of the 8-bit gray output parameter.

setOutput8BitGray

public void setOutput8BitGray(boolean output8BitGray)

If set, grayscale images with a bit depth less than 8 (1, 2, or 4) will be output in 8 bit form. The output values will occupy the full 8-bit range. For example, gray values 0, 1, 2, and 3 of a 2-bit image will be output as 0, 85, 170, and 255.

The decoding of non-grayscale images and grayscale images with a bit depth of 8 or 16 are unaffected by this setting.

The default is not to perform expansion. Grayscale images with a depth of 1, 2, or 4 bits will be represented using a MultiPixelPackedSampleModel and an IndexColorModel.

getPerformGammaCorrection

public boolean getPerformGammaCorrection()

Returns true if gamma correction is to be performed on the image data. The default is true.

If gamma correction is to be performed, the getUserExponent() and getDisplayExponent() methods are used in addition to the gamma value stored within the file (or the default value of 1/2.2 used if no value is found) to produce a single exponent using the formula:

 decoding_exponent = user_exponent/(gamma_from_file * display_exponent)
 

setPerformGammaCorrection

public void setPerformGammaCorrection(boolean performGammaCorrection)

Turns gamma corection of the image data on or off.

getUserExponent

public float getUserExponent()

Returns the current value of the user exponent parameter. By default, the user exponent is equal to 1.0F.

setUserExponent

public void setUserExponent(float userExponent)

Sets the user exponent to a given value. The exponent must be positive. If not, an IllegalArgumentException will be thrown.

The output image pixels will be placed through a transformation of the form:

 sample = integer_sample / (2^bitdepth - 1.0)
 decoding_exponent = user_exponent/(gamma_from_file * display_exponent)
 output = sample ^ decoding_exponent
 

where gamma_from_file is the gamma of the file data, as determined by the gAMA, sRGB, and/or iCCP chunks, and display_exponent is the exponent of the intrinsic transfer curve of the display, generally 2.2.

Input files which do not specify any gamma are assumed to have a gamma of 1/2.2; such images may be displayed on a CRT with an exponent of 2.2 using the default user exponent of 1.0.

The user exponent may be used in order to change the effective gamma of a file. If a file has a stored gamma of X, but the decoder believes that the true file gamma is Y, setting a user exponent of Y/X will produce the same result as changing the file gamma.

This parameter affects the decoding of all image types.

Throws:

IllegalArgumentException - if userExponent is negative.

getDisplayExponent

public float getDisplayExponent()

Returns the current value of the display exponent parameter. By default, the display exponent is equal to 2.2F.

setDisplayExponent

public void setDisplayExponent(float displayExponent)

Sets the display exponent to a given value. The exponent must be positive. If not, an IllegalArgumentException will be thrown.

The output image pixels will be placed through a transformation of the form:

 sample = integer_sample / (2^bitdepth - 1.0)
 decoding_exponent = user_exponent/(gamma_from_file * display_exponent)
 output = sample ^ decoding_exponent
 

where gamma_from_file is the gamma of the file data, as determined by the gAMA, sRGB, and/or iCCP chunks, and user_exponent is an additional user-supplied parameter.

Input files which do not specify any gamma are assumed to have a gamma of 1/2.2; such images should be decoding using the default display exponent of 2.2.

If an image is to be processed further before being displayed, it may be preferable to set the display exponent to 1.0 in order to produce a linear output image.

This parameter affects the decoding of all image types.

Throws:

IllegalArgumentException - if userExponent is negative.

getExpandGrayAlpha

public boolean getExpandGrayAlpha()

Returns the current setting of the gray/alpha expansion.

setExpandGrayAlpha

public void setExpandGrayAlpha(boolean expandGrayAlpha)

If set, images containing one channel of gray and one channel of alpha (GA) will be output in a 4-channel format (GGGA). This produces output that may be simpler to process and display.

This setting affects both images of color type 4 (explicit alpha) and images of color type 0 (grayscale) that contain transparency information.

By default, no expansion is performed.

getGenerateEncodeParam

public boolean getGenerateEncodeParam()

Returns true if an instance of PNGEncodeParam will be available after an image has been decoded via the getEncodeParam method.

setGenerateEncodeParam

public void setGenerateEncodeParam(boolean generateEncodeParam)

If set, an instance of PNGEncodeParam will be available after an image has been decoded via the getEncodeParam method that encapsulates information about the contents of the PNG file. If not set, this information will not be recorded and getEncodeParam() will return null.

getEncodeParam

public PNGEncodeParam getEncodeParam()

If getGenerateEncodeParam() is true, this method may be called after decoding has completed, and will return an instance of PNGEncodeParam containing information about the contents of the PNG file just decoded.

setEncodeParam

public void setEncodeParam(PNGEncodeParam encodeParam)

Sets the current encoder param instance. This method is intended to be called by the PNG decoder and will overwrite the current instance returned by getEncodeParam.