| java.lang.Object
 com.sun.media.jai.codec.PNGDecodeParam
| PNGDecodeParam | | public class PNGDecodeParam implements ImageDecodeParam(Code) | | 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.
|
| Constructor Summary | |
| public | PNGDecodeParam()
Constructs a default instance of PNGDecodeParam. |
| Method Summary | |
| public float | getDisplayExponent()
Returns the current value of the display exponent parameter. | | 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. | | public boolean | getExpandGrayAlpha()
Returns the current setting of the gray/alpha expansion. | | public boolean | getExpandPalette()
Returns true if palette-color images will be expanded to
produce full-color output. | | public boolean | getGenerateEncodeParam()
Returns true if an instance of
PNGEncodeParam will be available after an image
has been decoded via the getEncodeParam method. | | public boolean | getOutput8BitGray()
Returns the current value of the 8-bit gray output parameter. | | public boolean | getPerformGammaCorrection()
Returns true if gamma correction is to be performed
on the image data. | | public boolean | getSuppressAlpha()
Returns true if alpha (transparency) will
be prevented from appearing in the output. | | public float | getUserExponent()
Returns the current value of the user exponent parameter. | | public void | setDisplayExponent(float displayExponent)
Sets the display exponent to a given value. | | public void | setEncodeParam(PNGEncodeParam encodeParam)
Sets the current encoder param instance. | | 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). | | public void | setExpandPalette(boolean expandPalette)
If set, palette color images (PNG color type 3) will
be decoded into full-color (RGB) output images. | | 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. | | 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. | | public void | setPerformGammaCorrection(boolean performGammaCorrection)
Turns gamma corection of the image data on or off. | | public void | setSuppressAlpha(boolean suppressAlpha)
If set, no alpha (transparency) channel will appear in the
output image. | | public void | setUserExponent(float userExponent)
Sets the user exponent to a given value. |
| PNGDecodeParam | | public PNGDecodeParam()(Code) | | Constructs a default instance of PNGDecodeParam.
|
| getDisplayExponent | | public float getDisplayExponent()(Code) | | Returns the current value of the display exponent parameter.
By default, the display exponent is equal to 2.2F.
|
| getEncodeParam | | public PNGEncodeParam getEncodeParam()(Code) | | 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.
|
| getExpandGrayAlpha | | public boolean getExpandGrayAlpha()(Code) | | Returns the current setting of the gray/alpha expansion.
|
| getExpandPalette | | public boolean getExpandPalette()(Code) | | Returns true if palette-color images will be expanded to
produce full-color output.
|
| getGenerateEncodeParam | | public boolean getGenerateEncodeParam()(Code) | | Returns true if an instance of
PNGEncodeParam will be available after an image
has been decoded via the getEncodeParam method.
|
| getOutput8BitGray | | public boolean getOutput8BitGray()(Code) | | Returns the current value of the 8-bit gray output parameter.
|
| getPerformGammaCorrection | | public boolean getPerformGammaCorrection()(Code) | | Returns true if gamma correction is to be performed
on the image data. The default is false.
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)
|
| getSuppressAlpha | | public boolean getSuppressAlpha()(Code) | | Returns true if alpha (transparency) will
be prevented from appearing in the output.
|
| getUserExponent | | public float getUserExponent()(Code) | | Returns the current value of the user exponent parameter.
By default, the user exponent is equal to 1.0F.
|
| setDisplayExponent | | public void setDisplayExponent(float displayExponent)(Code) | | 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. |
| setEncodeParam | | public void setEncodeParam(PNGEncodeParam encodeParam)(Code) | | 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.
|
| setExpandGrayAlpha | | public void setExpandGrayAlpha(boolean expandGrayAlpha)(Code) | | 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.
|
| setExpandPalette | | public void setExpandPalette(boolean expandPalette)(Code) | | 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.
|
| setGenerateEncodeParam | | public void setGenerateEncodeParam(boolean generateEncodeParam)(Code) | | 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.
|
| setOutput8BitGray | | public void setOutput8BitGray(boolean output8BitGray)(Code) | | 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.
|
| setPerformGammaCorrection | | public void setPerformGammaCorrection(boolean performGammaCorrection)(Code) | | Turns gamma corection of the image data on or off.
|
| setSuppressAlpha | | public void setSuppressAlpha(boolean suppressAlpha)(Code) | | If set, no alpha (transparency) channel will appear in the
output image.
The default is to allow transparency to appear in the
output image.
|
| setUserExponent | | public void setUserExponent(float userExponent)(Code) | | 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. |
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