Pixelation in the RGBToHSV color conversion function

[bmeeder]

Hello again,

I am experiencing pixelation when performing RGBToHSV color conversion.

A picture of this can be found here:

Before the conversion process

http://www.andrew.cmu.edu/user/bmeeder/noConv.bmp

After the conversion process

http://www.andrew.cmu.edu/user/bmeeder/conv.bmp

Is there anything that I should know about this function that would affect how it is performing? The code that I am using is as follows:

void HSVThresholdGTVal_I(CBuffer *buf, RECTANGLE region, int val, int satisfyValue, int data)
{
#define iw buf->w()
#define ih buf->h()

assert(region.top >= 0 && region.top < region.bottom && region.left >= 0 && region.right > region.left);

//code to figure out the region of interest that we are going to be dealing with
int roiW, roiH;
int offset;
int tempSB;
int paneSB;

//the region of interest should be contained within the image
if(region.left < iw && region.top < ih)
{
if(region.right <= iw)
roiW = region.right - region.left;
else
roiW = iw - region.left;
if(region.bottom <= ih)
roiH = region.bottom - region.top;
else
roiH = ih - region.top;

IppiSize roi = {roiW, roiH};
offset = (region.top * buf->StepSize() + region.left)*3;

Ipp8u* temp = ippiMalloc_8u_C3(roiW, roiH, &tempSB);
Ipp8u* pane = ippiMalloc_8u_C1(roiW, roiH, &paneSB);

ippiRGBToHSV_8u_C3R(buf->Buffer() + offset, buf->StepSize(), temp, tempSB, roi);
//copy the right part of the buffer over
//data specifies whether hue, sat. or value is copied

ippiCopy_8u_C3C1R(temp + data, tempSB, pane, paneSB, roi);

//clear the region that we are looking at

ippiSet_8u_C3R(BLACK, buf->Buffer() + offset, buf->StepSize(), roi);

ippiCopy_8u_C1C3R(pane, paneSB, buf->Buffer() + offset, buf->StepSize(), roi);
ippiCopy_8u_C1C3R(pane, paneSB, buf->Buffer() + offset+1, buf->StepSize(), roi);
ippiCopy_8u_C1C3R(pane, paneSB, buf->Buffer() + offset+2, buf->StepSize(), roi);

}

#undef iw
#undef ih
}

Many thanks,

Brendan Meeder

[bmeeder]

Let me perhaps as a different question:

Does RGBToHSV perform the function on every single pixel in the image, or does it work on groups of pixels to increase performance?

Many thanks,

Brendan

[Vladimir_Dudnik]

Hi, ippiRGBToHSV work on pixel by pixel basis in reference implementation. Of course, it might use some optimization technics in optimized code. The pseudo code looks like that:

// Reference:
// David F.Rogers
// Procedural elements for computer graphics
// 1985.pp.(401-403)
//
// H is the hue red at 0 degrees, which has range [0 .. 360 degrees],
// S is the saturation,
// V is the value
// The RGB to HSV conversion algorithm in pseudocode:
// Value:
// V = max(R,G,B);
// Saturation:
// temp = min(R,G,B);
// if V = 0 then // achromatics case
// S = 0
// H = 0
// else // chromatics case
// S = (V - temp)/V
// Hue:
// Cr = (V - R) / (V - temp)
// Cg = (V - G) / (V - temp)
// Cb = (V - B) / (V - temp)
// if R = V then H = Cb - Cg
// if G = V then H = 2 + Cr - Cb
// if B = V then H = 4 + Cg - Cr
// H = 60*H
// if H < 0 then H = H + 360
//
// The HSV to RGB conversion algorithm in pseudocode:
// if S = 0 then
// R = G = B = V
// else
// if H = 360 then
// H = 0
// else
// H = H/60
// I = floor(H)
// F = H - I;
// M = V * ( 1 - S);
// N = V * ( 1 - S * F);
// K = V * ( 1 - S * (1 - F));
// if(I == 0)then{ R = V;G = K;B = M;}
// if(I == 1)then{ R = N;G = V;B = M;}
// if(I == 2)then{ R = M;G = V;B = K;}
// if(I == 3)then{ R = M;G = N;B = V;}
// if(I == 4)then{ R = K;G = M;B = V;}
// if(I == 5)then{ R = V;G = M;B = N;}
//
// in the range [0..IPP_MAX_8u ] for the 8u depth,
// in the range [0..IPP_MAX_16u] for the 16u depth,

Regards,
Vladimir

[ozgurovic]

Hello everybody,

I am using IPL2.5 (ok ancient tool, but at the end we are a university;)) I want to ask a question about the rgb2HSV tool used by IPL. I used the one embedded in IPL, and compared it with theoretical values, however I observed differences between them. (The theoretical values I used were the one described in here, and the formula described in Gonzalez's book with arccos)Does anybody know what conversion is using IPL's RGB2HSV tool?

[Vladimir_Dudnik]

IPL library not released for several years. You should know that there are University license for IPP, see IPP web page for more details

Regards,
Vladimir