DCTQuantFwd8x8LS

Performs level shift, forward DCT and quantization of an 8x8 block.

Syntax

IppStatus ippiDCTQuantFwd8x8LS_JPEG_8u16s_C1R(const Ipp8u* pSrc, int srcStep, Ipp16s* pDst, const Ipp16u* pQuantFwdTable);

IppStatus ippiDCTQuantFwd8x8LS_JPEG_16u16s_C1R(const Ipp16u* pSrc, int srcStep, Ipp16s* pDst, const Ipp32f* pQuantFwdTable);

Parameters

pSrc	Pointer to the 8x8 block in the source image.
srcStep	Distance in bytes between starts of consecutive lines in the source image.
pDst	Pointer to the destination 8x8 block of the quantized DCT coefficients.
pQuantFwdTable	Pointer to the quantization table for the encoder.

Description

The function ippiDCTQuantFwd8x8LS_JPEG is declared in the ippj.h file. It operates with ROI (see Regions of Interest in Intel IPP).

This function performs a forward DCT, quantization of DCT coefficients, and data conversion. Data from the unsigned Ipp8u range [0..255] are converted to the signed Ipp16s range [-128..127].

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

Example “Using Combined DCT Functions” shows how to use the function ippiDCTQuantFwd8x8LS_JPEG_8u16s_C1R.

Return Values

ippStsNoErr	Indicates no error.
ippStsNullPtrErr	Indicates an error condition if any of the specified pointers is NULL.

Using Combined DCT Function

Ipp8u pQuantRawTable[64] = { 16,  11,  12,  14,  12,  10,  16,  14,

                             13,  14,  18,  17,  16,  19,  24,  40,

                             26,  24,  22,  22,  24,  49,  35,  37,

                             29,  40,  58,  51,  61,  60,  57,  51,

                             56,  55,  64,  72,  92,  78,  64,  68,

                             87,  69,  55,  56,  80, 109,  81,  87,

                             95,  98, 103, 104, 103,  62,  77, 113,

                            121, 112, 100, 120,  92, 101, 103,  99};

Ipp8u src[8*8] = {  4, 4, 4, 4, 4, 4, 4, 4,

                    4, 3, 3, 3, 3, 3, 3, 4,

                    4, 3, 2, 2, 2, 2, 3, 4,

                    4, 3, 2, 1, 1, 2, 3, 4,

                    4, 3, 2, 1, 1, 2, 3, 4,

                    4, 3, 2, 2, 2, 2, 3, 4,

                    4, 3, 3, 3, 3, 3, 3, 4,

                    4, 4, 4, 4, 4, 4, 4, 4};

Ipp16s dst[64];

Ipp16u pQuantFwdTable[64];

int quality = 75;

ippiQuantFwdRawTableInit_JPEG_8u ( pQuantRawTable, quality );

ippiQuantFwdTableInit_JPEG_8u16u ( pQuantRawTable, pQuantFwdTable );

ippiDCTQuantFwd8x8LS_JPEG_8u16s_C1R ( src, 8, dst, pQuantFwdTable );

result:

pQuantRawTable (with quality)

 8  6  6  7  6  5  8  7

 7  7  9  9  8  0 12 20

13 12 11 11 12 25 18 19

15 20 29 26 31 30 29 26

28 28 32 36 46 39 32 34

44 35 28 28 40 55 41 44

48 49 52 52 52 31 39 57

61 56 50 60 46 51 52 50

        pQuantFwdTable

4096 5461 6554 4096 2731 1638 1260 1057

5461 5461 4681 3277 2521 1130 1092 1170

4681 4681 4096 2731 1638 1130  936 1170

4681 3641 2979 2185 1260  745  819 1057

3641 2979 1725 1170  964  596  630  840

2731 1820 1170 1024  799  630  575  712

1311 1024  840  745  630  537  546  643

 910  712  683  669  585  655  630  655

dst

-125 0 1 0 0 0 0 0

0 0 0 0 0 0 0 0

1 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0