HarrisCorner

Implements Harris corner detection algorithm.

Syntax

IppStatus ippiHarrisCorner_8u32f_C1R(const Ipp8u* pSrc, int srcStep, Ipp32f* pDst, int dstStep, IppiSize roiSize, IppiDifferentialKernel filterType, IppiMaskSize filterMask, Ipp32u avgWndSize, float k, float scale, IppiBorderType borderType, Ipp8u borderValue, Ipp8u* pBuffer);

IppStatus ippiHarrisCorner_32f_C1R(const Ipp32f* pSrc, int srcStep, Ipp32f* pDst, int dstStep, IppiSize roiSize, IppiDifferentialKernel filterType, IppiMaskSize filterMask, Ipp32u avgWndSize, float k, float scale, IppiBorderType borderType, Ipp32f borderValue, Ipp8u* pBuffer);

Include Files

ippcv.h

Domain Dependencies

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

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

Parameters

pSrc

Pointer to the source image.

srcStep

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

pDst

Pointer to the destination image.

dstStep

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

roiSize

Size of the source and destination image ROI in pixels.

filterType

Type of the derivative operator. Possible values are:

ippKernelSobel	Sobel filter
ippKernelScharr	Scharr filter
ippKernelCentralDiff	Central differences operator

filterMask

Size of the derivative filter aperture. The list of possible values depends on the filterType value:

Filter Type	Filter Mask
ippKernelSobel	ippMskSize3x3, ippMskSize5x5
ippKernelScharr	ippMskSize3x3
ippKernelCentralDiff	ippMskSize3x3

avgWndSize

Linear size of a neighborhood block for averaging.

k

Harris detector free coefficient.

scale

Destination image scale factor.

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.
ippBorderMirror	Border pixels are mirrored from the source image boundary pixels.

Mixed borders are also supported. They can be obtained by the bitwise operation OR between ippBorderRepl or ippBorderConst and the following flags:

ippBorderInMemTop
ippBorderInMemBottom
ippBorderInMemLeft
ippBorderInMemRight

Each of these flags means that for the corresponding border the outside pixels of the source image are in memory.

borderValue

Constant value(s) to assign to pixels of the constant border. This parameter is applicable only to the ippBorderConst border type. The ippiHarrisCorner function uses the specified constant value only at the first stage of the algorithm. At the third stage, the function uses zero constant border.

pBuffer

Pointer to the pre-allocated temporary buffer. To calculate the size of the temporary buffer, use the HarrisCornerGetBufferSize function.

Description

This function goes through the following stages to implement the Harris corner detection algorithm:

Computes I^{(x, y)}_x and I^{(x, y)}_y gradients for each (x, y) pixel of the image. The function computes gradients using the derivative operator specified by the filterType and filterMask parameters.
Computes products of the gradients at each (x, y) pixel of the image:
Performs averaging of the products of gradients over a rectangular neighborhood block at each pixel of the image. The block size is specified by the avgWndSize value.
Defines 2x2 gradient covariance matrix H^{(x , ^y)} over a rectangular neighborhood block for each (x, y) pixel of the image.
Computes the corner response at each pixel of the image:

where

k is the Harris detector free parameter

The first and third stages of the function algorithm are filtering operations; they use border processing approach that is specified by the borderType parameter.

The scale parameter is applied to the output image.

Before using this function, compute the size of the temporary work buffer using the HarrisCornerGetBufferSize function.

Return Values

ippStsNoErr	Indicates no error. Any other value indicates an error or a warning.
ippStsNullPtrErr	Indicates an error when pSrc, pDst, or pBufferSize is `NULL`.
ippStsSizeErr	Indicates an error in the following cases: when roiSize is less than, or equal to zero when avgWndSize is equal to zero
ippStsNotEvenStepErr	Indicates an error when one of the step values is not divisible by 4 for floating point images.
ippStsFilterTypeErr	Indicates an error when filterType has an illegal value.
ippStsMaskSizeErr	Indicates an error when filterMask has an illegal value.
ippStsBorderErr	Indicates an error when borderType has an illegal value.
ippStsStepErr	Indicates an error when srcStep or dstStep has a negative value.
ippStsInplaceModeNotSupportedErr	Indicates an error when pSrc and pDst point to the same image.

Example

The code example below demonstrates how to use the ippiHarrisCorner_8u32f_C1R and ippiHarrisCornerGetBufferSize functions.

    ...
    int    bufSize = 0;
    Ipp8u* pBuffer  = 0;
    Ipp32u numChannels = 1;
    IppStatus status = ippStsNoErr;
    IppiBorderType borderType = ippBorderRepl;
    IppiDifferentialKernel filterType = ippFilterSobel;
    IppiMaskSize filterMask = ippMskSize5x5;
    Ipp32u avgWndSize = 3;
    Ipp32f scale = 1.0f;

    /* Computes the temporary work buffer size */
    status = ippiHarrisCornerGetBufferSize(roiSize, filterMask, avgWndSize, ipp8u, numChannels, &bufSize);

    /* Memory allocation */
    if (status != ippStsNoErr) pBuffer = ippsMalloc_8u(bufSize);

    if (pBuffer != NULL)
    {
        /* Harris Corner processing */
        status = ippiHarrisCorner_8u32f_C1R(pSrc, srcStep, pDst, dstStep, roiSize, filterType, filterMask, avgWndSize, 0.04f,
            scale, borderType, 0, pBuffer);

        ippsFree(pBuffer);
    }
    ...