I am a subclass of ImageReadWriter that decodes Portable Network Graphics
(PNG) images.

Submitted by Duane Maxwell

	chunks
	processBackgroundChunk processIDATChunk processIHDRChunk processInterlaced processNextChunk processNonInterlaced processPLTEChunk processPhysicalPixelChunk processTransparencyChunk

	filtering
	filterAverage: filterHorizontal: filterNone: filterPaeth: filterScanline:count: filterVertical: paethPredictLeft:above:aboveLeft:

	miscellaneous
	doPass: grayColorsFor:

	pixel copies
	copyPixels: copyPixels:at:by: copyPixelsGray: copyPixelsGray:at:by: copyPixelsGrayAlpha: copyPixelsGrayAlpha:at:by: copyPixelsIndexed: copyPixelsIndexed:at:by: copyPixelsRGB: copyPixelsRGB:at:by: copyPixelsRGBA: copyPixelsRGBA:at:by:

	accessing	top
	debugging
	nextImage Dencoding an image on stream and answer the image.
	understandsImageFormat Test to see if the image stream format is understood by this decoder. This should be implemented in each subclass of ImageReadWriter so that a proper decoder can be selected without ImageReadWriter having to know about all possible image file types.

	chunks	top
	processBackgroundChunk Transcript show: ' BACKGROUND: ',chunk printString.
	processIDATChunk
	processIHDRChunk
	processInterlaced
	processNextChunk
	processNonInterlaced
	processPLTEChunk
	processPhysicalPixelChunk Transcript show: ' PHYSICAL: ',chunk printString.
	processTransparencyChunk Transcript show: ' TRANSPARENCY ',chunk printString.

	filtering	top
	filterAverage: Use the average of the pixel to the left and the pixel above as a predictor
	filterHorizontal: Use the pixel to the left as a predictor
	filterNone:
	filterPaeth: Select one of (the pixel to the left, the pixel above and the pixel to above left) to predict the value of this pixel
	filterScanline:count:
	filterVertical: Use the pixel above as a predictor
	paethPredictLeft:above:aboveLeft: Predicts the value of a pixel based on nearby pixels, based on Paeth (GG II, 1991)

	miscellaneous	top
	doPass: Certain interlace passes are skipped with certain small image dimensions
	grayColorsFor: return a color table for a gray image

	pixel copies	top
	copyPixels: Handle non-interlaced pixels of supported colorTypes
	copyPixels:at:by: Handle interlaced pixels of supported colorTypes
	copyPixelsGray: Handle non-interlaced grayscale color mode (colorType = 0)
	copyPixelsGray:at:by: Handle interlaced grayscale color mode (colorType = 0)
	copyPixelsGrayAlpha: Handle non-interlaced grayscale with alpha color mode (colorType = 4)
	copyPixelsGrayAlpha:at:by: Handle interlaced grayscale with alpha color mode (colorType = 4)
	copyPixelsIndexed: Handle non-interlaced indexed color mode (colorType = 3)
	copyPixelsIndexed:at:by: Handle interlaced indexed color mode (colorType = 3)
	copyPixelsRGB: Handle non-interlaced RGB color mode (colorType = 2)
	copyPixelsRGB:at:by: Handle interlaced RGB color mode (colorType = 2)
	copyPixelsRGBA: Handle non-interlaced RGBA color modes (colorType = 6)
	copyPixelsRGBA:at:by: Handle interlaced RGBA color modes (colorType = 6)

	as yet unclassified	top
	createAFormFrom:
	debugging:
	initialize PNGReadWriter initialize
	insertMorph:named:into:
	test1 PNGReadWriter test1