RGB to HSV and vice versa conversion.

[heinz85]

Hello.
Can anybody refer me to a reliable code snippet of RGB to HSV and vice versa conversion?

Thanks,
Heinrich

[Thallius]

-(void)hsvToRGB:(struct rgbhsvColor*)color
{
	if(color->saturation==0.0)
	{
		color->red=round(color->vvalue*255.0);
		color->green=round(color->vvalue*255.0);
		color->blue=round(color->vvalue*255.0);
	}
	else 
	{
		float hTemp=0.0;
 
		if(color->hue==360.0)
			hTemp=0.0;
		else
			hTemp=color->hue/60.0;
 
		int i=trunc(hTemp);
		float f=hTemp-i;
 
		float p=color->vvalue*(1.0-color->saturation);
		float q=color->vvalue*(1.0-(color->saturation*f));
		float t=color->vvalue*(1.0-(color->saturation*(1.0-f)));
 
		switch (i) 
		{
			default:
			case 0:
			case 6:
				color->red=round(color->vvalue*255.0);
				color->green=round(t*255.0);
				color->blue=round(p*255.0);
				break;
			case 1:
				color->red=round(q*255.0);
				color->green=round(color->vvalue*255.0);
				color->blue=round(p*255.0);
				break;
			case 2:
				color->red=round(p*255.0);
				color->green=round(color->vvalue*255.0);
				color->blue=round(t*255.0);
				break;
			case 3:
				color->red=round(p*255.0);
				color->green=round(q*255.0);
				color->blue=round(color->vvalue*255.0);
				break;
			case 4:
				color->red=round(t*255.0);
				color->green=round(p*255.0);
				color->blue=round(color->vvalue*255.0);
				break;
			case 5:
				color->red=round(color->vvalue*255.0);
				color->green=round(p*255.0);
				color->blue=round(q*255.0);
				break;
		}
 
	}
	return;
}
 
// calc HSV values of rgbhsvColor from RGB values
-(void)rgbToHSV:(struct rgbhsvColor*)color
{
	UBYTE maxRGBValue=MAX(MAX(color->red,color->green),color->blue);
	float minValue=MIN(MIN(color->red,color->green),color->blue);
	float maxValue=maxRGBValue;
	float hue,saturation,vvalue,delta;
 
	minValue=minValue/255.0;
	maxValue=maxValue/255.0;
 
	vvalue=maxValue;
	delta=vvalue-minValue;
 
	if(delta==0)
		saturation=0;
	else 
		saturation=round(delta/vvalue);
 
	if(saturation==0)
		hue=0;
	else 
	{
		if(color->red==maxRGBValue)
			hue=60.0*(float)(color->green-color->blue)/255.0/delta;
		else 
		{
			if(color->green==maxRGBValue)
				hue=120.0+60.0*(float)(color->blue-color->red)/255.0/delta;
			else 
			{
				if(color->blue==maxRGBValue)
					hue=240.0+60.0*(float)(color->red-color->green)/255.0/delta;
			}
		}
		if(hue<0.0)
			hue+=360.0;
	}
	color->hue=round(hue);
	color->saturation=round(saturation);
	color->vvalue=round(vvalue);
	return;	
}

hope that helps

Thallius

[heinz85]

if(delta==0)
saturation=0;
???
are you sure it is not:

if (maxValue==0) saturation = 0; ?