Intel® Integrated Performance Primitives (Intel® IPP) Developer Guide and Reference

ID 790148
Date 3/22/2024
Public
Document Table of Contents

FilterSobel

Filters an image using a Sobel filter.

Syntax

IppStatus ippiFilterSobel_<mod>(const Ipp<srcdatatype>* pSrc, int srcStep, Ipp<dstdatatype>* pDst, int dstStep, IppiSize dstRoiSize, IppiMaskSize maskSize, IppNormType normType, IppiBorderType borderType, Ipp<srcdatatype> borderValue, Ipp8u* pBuffer);

Supported values for mod:

8u16s_C1R 16s32f_C1R 16u32f_C1R 32f_C1R

IppStatus ippiFilterSobel_<mod>_T(const Ipp8u* pSrc, int srcStep, Ipp16s* pDst, int dstStep, IppiBorderType border, const Ipp8u borderValue, IppiFilterSobelSpec_T* pSpec, Ipp8u* pBuffer);

Supported values for mod:

8u16s_C1R_T

Include Files

ippi.h

Domain Dependencies

Headers: ippcore.h, ippvm.h, ipps.h

Libraries: ippcore.lib, ippvm.lib, ipps.lib

Parameters

pSrc

Pointer to the source image ROI.

srcStep

Distance, in bytes, between the starting points of consecutive lines in the source image.

pDst

Pointer to the destination image ROI.

dstStep

Distance, in bytes, between the starting points of consecutive lines in the destination image.

dstRoiSize

Size of the source and destination ROI in pixels.

maskSize

Size of the predefined mask. Possible values are ippMskSize3x3 or ippMskSize5x5.

normType

Normalization mode of IppNormType.

borderType

Type of border. Possible values are:

ippBorderConst

Values of all border pixels are set to constant.

ippBorderRepl

Border is replicated from the edge pixels.

ippBorderInMem

Border is obtained from the source image pixels in memory.

Mixed borders are also supported. They can be obtained by the bitwise operation OR between any of the ippBorderRepl or ippBorderConst values and the ippBorderInMemTop, ippBorderInMemBottom, ippBorderInMemLeft, ippBorderInMemRight values.

borderValue

Constant value to assign to pixels of the constant border. This parameter is applicable only to the ippBorderConst border type.

pBuffer

Pointer to the work buffer.

Description

Before using this function, you need to compute the size of the work buffer pBuffer using the ippiFilterSobelBufferSize function.

Call the ippiFilterSobelInit_T function before using the ippiFilterSobel*_T function.

This function applies a Sobel filter to the source image with the specified kernel size and normalization type. The values of border pixels are assigned in accordance with the borderType and borderValue parameters. The kernel of the filter is a matrix of 3x3 or 5x5 size depending on the maskSize value. The formulas below describe the algorithm for the 3x3 and 5x5 Sobel operators.

3x3 Sobel operator:

5x5 Sobel operator:

where

  • A is the source image

  • * is the 2D convolution operator

  • Gx and Gy are horizontal and vertical magnitude of the source image, respectively

Sobel filter output G, as overall gradient magnitude, is generated through L1 and L2 normalization of Gx and Gy.

L1 normalization:

L2 normalization:

Return Values

ippStsNoErr

Indicates no error.

ippStsNullPtrErr

Indicates an error when one of the specified pointers is NULL.

ippStsSizeErr

Indicates an error when dstRoiSize has a field with a zero or negative value.

ippStsMaskSizeErr

Indicates an error when maskSize has an illegal value.

ippStsStepErr

Indicates an error when srcStep or dstStep is less than, or equal to zero.

ippStsNotEvenStepErr

Indicates an error when one of the step values is not divisible by 4 for floating-point images, or by 2 for short-integer images.

ippStsBorderErr

Indicates an error when borderType has an illegal value.

Example

The code example below demonstrates how to use the ippiFilterSobelGetBufferSize and ippiFilterSobel_8u16s_C1R functions.

IppStatus filter_sobel_8u16s_c1( void ) {
    Ipp8u pSrc[9*8] =
    {
        0, 1, 2, 120, 121, 122, 50, 51, 52,
        1, 2, 3, 121, 122, 123, 52, 52, 53,
        3, 4, 5, 130, 131, 132, 63, 64, 65,
        4, 5, 6, 131, 132, 133, 64, 65, 66,
        5, 6, 7, 132, 133, 134, 65, 66, 67,
        8, 7, 6, 134, 133, 132, 67, 66, 65,
        7, 6, 5, 133, 132, 131, 66, 65, 64,
        6, 5, 4, 132, 131, 130, 65, 64, 63
    };
    Ipp16s   pDst[8*7];
    IppiSize roiSize = {8, 7};
   	IppiMaskSize mask = ippMskSize3x3;
    IppiBorderType borderType = ippBorderConst | ippBorderInMemTop | ippBorderInMemRight;
    int     srcStep = 9 * sizeof(Ipp8u);
    int     dstStep = 8 * sizeof(Ipp16s);
    int     bufferSize;
    IppStatus status;
    Ipp8u   *pBuffer;
    IppNormType normType = ippNormL1;

    ippiFilterSobelGetBufferSize(roiSize, mask, normType, ipp8u, ipp16s, 1, &bufferSize);
    pBuffer = ippsMalloc_8u(bufferSize);
    status = ippiFilterSobel_8u16s_C1R(pSrc+srcStep, srcStep, pDst, dstStep, roiSize, mask, normType, borderType, 33, pBuffer);
    ippsFree(pBuffer);

    return status;
}

The result is as follows:

pDst -->
    132     20    502    516     48    322    330     58
    126     20    516    530     48    316    322     58
    118     16    512    512     16    280    280     16
    118     12    510    512      8    272    276      8
    110      4    510    508      8    272    268      8
    114     16    516    516     16    272    272     16
    162    114    398    652    402    526    394    134