Class PNGDecodeParam
- All Implemented Interfaces:
Serializable
,Cloneable
,ImageDecodeParam
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:
-
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionfloat
Returns the current value of the display exponent parameter.IfgetGenerateEncodeParam()
istrue
, this method may be called after decoding has completed, and will return an instance ofPNGEncodeParam
containing information about the contents of the PNG file just decoded.boolean
Returns the current setting of the gray/alpha expansion.boolean
Returns true if palette-color images will be expanded to produce full-color output.boolean
Returnstrue
if an instance ofPNGEncodeParam
will be available after an image has been decoded via thegetEncodeParam
method.boolean
Returns the current value of the 8-bit gray output parameter.boolean
Returnstrue
if gamma correction is to be performed on the image data.boolean
Returnstrue
if alpha (transparency) will be prevented from appearing in the output.float
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 ofPNGEncodeParam
will be available after an image has been decoded via thegetEncodeParam
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.
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Constructor Details
-
PNGDecodeParam
public PNGDecodeParam()Constructs a default instance ofPNGDecodeParam
.
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Method Details
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getSuppressAlpha
public boolean getSuppressAlpha()Returnstrue
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.
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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 anIndexColorModel
. -
getPerformGammaCorrection
public boolean getPerformGammaCorrection()Returnstrue
if gamma correction is to be performed on the image data. The default istrue
.If gamma correction is to be performed, the
getUserExponent()
andgetDisplayExponent()
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)
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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, anIllegalArgumentException
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
wheregamma_from_file
is the gamma of the file data, as determined by thegAMA
,sRGB
, and/oriCCP
chunks, anddisplay_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
- ifuserExponent
is negative.
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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, anIllegalArgumentException
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
wheregamma_from_file
is the gamma of the file data, as determined by thegAMA
,sRGB
, and/oriCCP
chunks, anduser_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
- ifuserExponent
is negative.
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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.
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getGenerateEncodeParam
public boolean getGenerateEncodeParam()Returnstrue
if an instance ofPNGEncodeParam
will be available after an image has been decoded via thegetEncodeParam
method. -
setGenerateEncodeParam
public void setGenerateEncodeParam(boolean generateEncodeParam) If set, an instance ofPNGEncodeParam
will be available after an image has been decoded via thegetEncodeParam
method that encapsulates information about the contents of the PNG file. If not set, this information will not be recorded andgetEncodeParam()
will returnnull
. -
getEncodeParam
IfgetGenerateEncodeParam()
istrue
, this method may be called after decoding has completed, and will return an instance ofPNGEncodeParam
containing information about the contents of the PNG file just decoded. -
setEncodeParam
Sets the current encoder param instance. This method is intended to be called by the PNG decoder and will overwrite the current instance returned bygetEncodeParam
.
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