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);
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; 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
The function ippiMinEigenVal is declared in the ippcv.h file. It 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. 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 (λ ≥ 0) 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. |