MinEigenVal output normalization depends from derivative kernels

MinEigenVal output normalization depends from derivative kernels

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Lorenzo C.
Mo, 17/12/2012 - 06:43

Hi,

while comparing the minimum eigenvalue computed for an image using ippiEigenValsVecs_8u32f_C1R / ippiEigenValsVecs_32f_C1R with the same feature evaluated from scratch with the given formulas, it seems that the output is being normalized by a factor that depends from the employed derivative kernel. In particular, results are normalized by 4080 (255 << 4) and 65280 (255 << 8) in case of Sobel 3x3 and Sobel 5x5, respectively. The normalization factor for Scharr 3x3 seems about 6661.23.... where does this values come from? Anybody can answer?

thanks

PS: i am using IPP 6.0

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Chao Y (Intel)
Fr, 28/12/2012 - 00:28

IPP computer vision functionality corresponds to OpenCV one – so normalization is done by the the same way as in OpenCV (in order to be compatible with OpenCV), so Normalization is as the following ways

…………
denom = 1.0f/(Ipp32f)((1<<(2*apertureSize-2))*255);
if (kernType==ippKernelSobel) {
…………………….
} else { // kernType==ippKernelScharr
denom *= 0.6125f;
………………………………
}
……………
calcValues (bufXXomp,bufYYomp,bufXYomp,step32f,pEigenVV,eigStep,roiSize,denom,sign)

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Lorenzo C.
Mi, 02/01/2013 - 00:24

Many thanks, compatibility with OpenCV makes sense.

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