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.
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