DCTQuantInv8x8To4x4LS_JPEG, DCTQuantInv8x8To2x2LS_JPEG

Performs dequantization, inverse DCT, level shift, and downsampling of an 8x8 block.

Syntax

IppStatus ippiDCTQuantInv8x8To4x4LS_JPEG_16s8u_C1R(const Ipp16s* pSrc, Ipp8u* pDst, int dstStep, const Ipp16u* pQuantInvTable);

IppStatus ippiDCTQuantInv8x8To2x2LS_JPEG_16s8u_C1R(const Ipp16s* pSrc, Ipp8u* pDst, int dstStep, const Ipp16u* pQuantInvTable);

Parameters

pSrc

Pointer to the 8x8 block of quantized DCT coefficients.

pDst

Pointer to the block in the destination image.

dstStep

Distance in bytes between starts of consecutive lines in the destination image.

pQuantInvTable

Pointer to the quantization table for the decoder.

Description

These functions are declared in the ippj.h file. They operate with ROI (see Regions of Interest in Intel IPP).

These functions perform an inverse DCT, dequantization of DCT coefficients, downsamling and data conversion. The function ippiDCTQuantInv8x8To4x4LS_JPEG perfroms downsampling with factor 1:2, that is the output block contains 4x4 elements. The function ippiDCTQuantInv8x8To2x2LS_JPEG perfroms downsampling with factor 1:4, that is the output block contains 2x2 elements.

The functions convert data from the signed Ipp16s range [-128..127] to the unsigned Ipp8u range [0..255].

The function uses a quantization table suitable for fast decoding. This table must be prepared using the function ippiQuantInvTableInit_JPEG.

Return Values

ippStsNoErr

Indicates no error.

ippStsNullPtrErr

Indicates an error condition if any of the specified pointers is NULL.

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