ColorTwist saturation giving wrong results

ColorTwist saturation giving wrong results

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I am using ColorTwist for image saturation manipulation. The image is 8u 3c.

[c]

// BGR to RGB

int swapStep;

Ipp8u* swap = ippiMalloc_8u_C3(roi.width, roi.height, &swapStep);

int swapOrder[] = { 2, 1, 0 };

status = ippiSwapChannels_8u_C3R(img, lineStep, swap, swapStep, roi, swapOrder);

// convert to float and scale 0.f - 1.f

int imgFStep;

Ipp32f* imgF = ippiMalloc_32f_C3(roi.width, roi.height, &imgFStep);

IppStatus ippStat = ippiScale_8u32f_C3R(swap, swapStep, imgF, imgFStep, roi, 0.f, 1.f);

const float rf = 0.299f;

const float gf = 0.587f;

const float bf = 0.114f;

float s = -1.f;

float a = (1.f - s) * rf + s;

float b = (1.f - s) * rf;

float c = (1.f - s) * rf;

float d = (1.f - s) * gf;

float e = (1.f - s) * gf + s;

float f = (1.f - s) * gf;

float g = (1.f - s) * bf;

float h = (1.f - s) * bf;

float i = (1.f - s) * bf + s;

const Ipp32f twist[3][4] =

{

a, b, c, 0.f,

d, e, f, 0.f,

g, h, i, 0.f,

};

ippStat = ippiColorTwist_32f_C3IR(imgF, imgFStep, roi, twist);

ippStat = ippiScale_32f8u_C3R(imgF, imgFStep, img, lineStep, roi, 0.f, 1.f);

// swap back to BGR

ippStat = ippiSwapChannels_8u_C3IR(img, lineStep, roi, swapOrder);

[/c]

 But the resulting image is green? It's supposed to be desaturated - I saw another thread with this issue - but I am not using any alpha channels.

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