Convert RGB to HSV

[Richmond Mathewson]

The "magic numbers" (i.e. the conversion algorithms) are laid out very 
clearly here:

http://en.wikipedia.org/wiki/HSB_color_space

which seems to predate Monte Goulding.

James Hurley wrote:
> What I have been using are the following two functions. I believe they 
> originated with Monte Goulding. (With a slight addition to allow for a 
> single parameter input containing the rgb values.)
> They have been VERY useful. There are times when HSV is critical.
> (Of course neither is useful in getting the RGB--or HSV--values from 
> the color names.)
>
> Jim Hurley
>
> function RGBtoHSV r, g, b
>    if the paramcount is 1 then
>       put item 3 of r into b
>       put item 2 of r into g
>       put item 1 of r into r
>    end if
>    local maxv, minv, diff, s, rc, gc, bc, h
>    set the numberFormat to "0.###############"
>    put r / 255 into r
>    put g / 255 into g
>    put b / 255 into b
>    put max(r,g,b) into maxv
>    put min(r,g,b) into minv
>    put maxv - minv into diff
>    if maxv <> 0 and diff <> 0 then
>       put diff / maxv into s
>       put (maxv - r) / diff into rc
>       put (maxv - g) / diff into gc
>       put (maxv - b) / diff into bc
>       if r = maxv then put bc - gc into h
>       else if g = maxv then put 2 + rc - bc into h
>       else if b = maxv then put 4 + gc - rc into h
>       multiply h by 60
>       if h < 0 then
>          add 360 to h
>       end if
>    else
>       put 0 into s
>       put 0 into h
>    end if
>    return round(h),round(s * 100),round(maxv * 100)
> end RGBtoHSV
>
> function HSVtoRGB h, s, v
>      if the paramcount is 1 then
>       put item 3 of h into v
>       put item 2 of h into s
>       put item 1 of h into h
>    end if
>   local rgb, i, f, p, q, t
>   set the numberFormat to "0.###############"
>   divide s by 100
>   divide v by 100
>   if s is 0 then put v,v,v into rgb
>   else
>     divide h by 60
>     put trunc(h) into i
>     put h - i into f
>     put v * (1 - s) into p
>     put v * (1 - s * f) into q
>     put v * (1 - s * (1- f)) into t
>     if i is 0 then put v,t,p into rgb
>     if i is 1 then put q,v,p into rgb
>     if i is 2 then put p,v,t into rgb
>     if i is 3 then put p,q,v into rgb
>     if i is 4 then put t,p,v into rgb
>     if i is 5 then put v,p,q into rgb
>   end if
>   return round(item 1 of rgb * 255), round(item 2 of rgb * 255), 
> round(item 3 of rgb * 255)
> end HSVtoRGB
>
>
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