Intel® Integrated Performance Primitives Developer Guide and Reference

ID 790148
Date 11/07/2023
Public

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Document Table of Contents

MinEigenVal

Calculates the minimal eigen value of image blocks for corner detection.

Syntax

IppStatus ippiMinEigenVal_8u32f_C1R(const Ipp8u* pSrc, int srcStep, Ipp32f* pMinEigenVal, int minValStep, IppiSize roiSize, IppiKernelType kernType, int apertureSize, int avgWindow, Ipp8u* pBuffer);

IppStatus ippiMinEigenVal_32f_C1R(const Ipp32f* pSrc, int srcStep, Ipp32f* pMinEigenVal, int minValStep, IppiSize roiSize, IppiKernelType kernType, int apertureSize, int avgWindow, 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 ROI.
srcStep
Distance in bytes between starts of consecutive lines in the source image.
pMinEigenVal
Pointer to the image that is filled with the minimal eigen values.
minValStep
Distance in bytes between starts of consecutive lines in the output image.
roiSize
Size of the source image ROI in pixels.
kernType
Specifies the type of kernel used to compute derivatives, possible values are:

ippKernelSobel

Sobel kernel 3x3 or 5x5

ippKernelSobelNeg

Negative Sobel kernel 3x3 or 5x5

ippKernelScharr

Scharr kernel 3x3
apertureSize
Size of the derivative operator in pixels, possible values are 3 or 5.
avgWindow
Size of the averaging window in pixels, possible values are 3 or 5.
pBuffer
Pointer to the temporary buffer.

Description

This function operates with ROI (see Regions of Interest in Intel IPP). This function takes a block around the pixel and computes the first derivatives Dx and Dy. When using the MinEigenVal function, you need to verify that the processing pixels beyond the ROI are available in memory. This operation is performed for every pixel of the image using either Sobel or Scharr kernel in accordance with the kernType parameter. The size of the Sobel kernel may be specified the parameter apertureSize. If this parameter is set to 3, the function used 3x3 kernel, if it is set to 5, the function uses 5x5 kernel. Only 3x3 size is available for the Scharr kernel, therefore the parameter apertureSize must be set to 3 if the Scharr kernel is used.

CAUTION:

If the parameter apertureSize is set to 5 for operation with the Scharr kernel, the function returns error status.

Then, the function computes the minimal eigen value λ (λ0) of the following matrix:



The summation is performed over the full block with averaging over the blurring window with size avgWindow.

The function requires a temporary working buffer; its size should be computed previously by calling the function ippiMinEigenValGetBufferSize.

CAUTION:

The parameters apertureSize and avgWindow must be the same for both functions ippiMinEigenValGetBufferSize and ippiMinEigenVal.

Return Values

ippStsNoErr

Indicates no error. Any other value indicates an error or a warning.

ippStsNullPtrErr

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

ippStsSizeErr

Indicates an error condition if pRoiSize has a field with zero or negative value, or if apertureSize or avgWindow has an illegal value; or if kernType has wrong value.

ippStsStepErr

Indicates an error condition if srcStep is less than roiSize.width*<pixelSize>, or eigenvvStep is less than roiSize.width*sizeof(Ipp32f).

ippStsNotEvenStepErr

Indicates an error condition if steps for floating-point images are not divisible by 4.