Re: RGB->HSI->RGB

Pete wrote:

> Hello
> 
> I'm having quantisation problems swapping between different colour spaces
> in a reversible way and wondered if anyone had a solution or a suggestion
> to the problem.
> 
> At present I'm using fp arithmetic to convert 3 byte rgb to 3 byte hsi.
> Unfortunately the reverse of this procedure does not give exactly the same
> rgb and after a few loops around this process there is a significant
> shift.

Have you already tried this with floating point values? Since the conversion
functions use real numbers, using fixed point / integer variables doesn't
seem to be the best way here.  An exact solution to problem is not
possibkle at all, I think (Just look at all those PI's in the formulas...)
Also you should think about the fact if it's really appropiate to convert
the image into another color space. In many applications its more useful to
create a HSI image from an RGB image and retain the original.
 
> I suppose one solution would be to use some form of look-up table and its
> inverse, but the number of permutations seems too large for that.

I agree with that. 

-- 
Dipl.-Inform. Hendrik Belitz
Central Laboratory of Electronics
Research Center Juelich