vImage Decompression Filtering Reference

Framework	Accelerate/vImage
Companion guide	vImage Programming Guide
Declared in	BasicImageTypes.h

Overview

The vImage framework provides one function for filtering data prior to decompression.

Functions

vImagePNGDecompressionFilter

Performs PNG decompression filtering.

vImage_Error  vImagePNGDecompressionFilter( const vImage_Buffer *buffer,
   vImagePixelCount    startScanline,
   vImagePixelCount    scanlineCount,
   uint32_t   bitsPerPixel,
   uint32_t  filterMethodNumber,
   uint32_t  filterType,
   vImage_Flags flags)

Parameters

buffer: On input, the image data to filter. On output, the filtered data. The filtering is always applied in place.
startScanline: The starting scanline.
scanlineCount: The number of scanlines in the buffer.
bitsPerPixel: The bits per pixel.
filterMethodNumber: The filter method number. You must pass 0, because this is the only filtering method offered by this function.
filterType: The filtering algorithm to apply to the image data. For filter method 0, you can pass any of the constants described in “PNG Filter Types.”
flags: The options to use when performing this operation. Set the kvImageDoNotTile flag if you plan to perform your own tiling or use multithreading. See vImage Data Types and Constants Reference for a complete description of vImage processing flags.

Discussion

This function implements PNG decompression filtering for filter method 0 of the PNG standard, section 9.2, as described in: http://www.w3.org/TR/PNG-Filters.html. When a pixel that is needed for a filtering calculation falls outside the source buffer, its value is presumed to be 0.

Availability

Available in iOS 5.0 and later.

Declared In

BasicImageTypes.h

Constants

PNG Filter Types

Filtering algorithms to apply to image data before compressing the data.

enum
{
   
   kvImage_PNG_FILTER_VALUE_NONE  = 0,
   kvImage_PNG_FILTER_VALUE_SUB   = 1,
   kvImage_PNG_FILTER_VALUE_UP    = 2,
   kvImage_PNG_FILTER_VALUE_AVG   = 3,
   kvImage_PNG_FILTER_VALUE_PAETH = 4
};