#321 wrong calculation RGB gamma in YUV

[alexey]

RGB gammacorrection in filter "Picture properties" wrong calculated, if input colorspace is YUV.

See attachment for image, in which you see difference between processing in RGB, and YUV colorspace, and source videos in RGB and YUV colorspace for test.

[alexey]

image with processing in RGB and YUV

[alexey]

erroneous code in the file TimgFilterLuma.cpp

void TimgFilterGammaRGB::processGammaYUV(...) {
...
double gY = 1.0/(0.299*gammaR+0.587*gammaG+0.114*gammaB);
double gU = 1.0/sqrt (gammaB / gammaG);
double gV = 1.0/sqrt (gammaR / gammaG);
for(int i=0; i<256; i++)
{
gammaTabYUV[0][i]=(unsigned char)(255.0*pow((i/255.0),gY));
gammaTabYUV[1][i]=(unsigned char)(255.0*pow((i/255.0),gU));
gammaTabYUV[2][i]=(unsigned char)(255.0*pow((i/255.0),gV));
}
...
}

YUV can not be converted using color mapping, only RGB.
you must convert YUV to RGB, perform gamma-processing by color mapping, and then convert RGB to YUV.

[alexey]

Video in YUV colorspace

[alexey]

Video in RGB colorspace