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Convert HSV colorspace to RGB (Tcl recipe) by andreas kupries
ActiveState Code (http://code.activestate.com/recipes/133527/)

Author: Jeff Hobbs.

Converts a color specified as Hue, Saturation and Value into an RGB triple. The result can be processed by "dec2rgb" (See recipe "Color Manipulation").

Tcl, 35 lines
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# hsv2rgb --
#
#   Convert hsv to rgb
#
# Arguments:
#   h		hue
#   s		saturation
#   v		value
# Results:
#   Returns an rgb triple from hsv
# 
proc hsv2rgb {h s v} {
    if {$s <= 0.0} {
	# achromatic
	set v [expr {int($v)}]
	return "$v $v $v"
    } else {
	set v [expr {double($v)}]
        if {$h >= 1.0} { set h 0.0 }
        set h [expr {6.0 * $h}]
        set f [expr {double($h) - int($h)}]
        set p [expr {int(256 * $v * (1.0 - $s))}]
        set q [expr {int(256 * $v * (1.0 - ($s * $f)))}]
        set t [expr {int(256 * $v * (1.0 - ($s * (1.0 - $f))))}]
	set v [expr {int(256 * $v)}]
        switch [expr {int($h)}] {
            0 { return "$v $t $p" }
            1 { return "$q $v $p" }
	    2 { return "$p $v $t" }
	    3 { return "$p $q $v" }
	    4 { return "$t $p $v" }
	    5 { return "$v $p $q" }
        }
    }
}
Tags: graphics, math

3 comments

Open Geek 18 years, 8 months ago  # | flag

If you're looking to convert colorspaces, there is a python builtin module colorsys that does that stuff: http://aspn.activestate.com/ASPN/docs/ActivePython/2.4/python/lib/module-colorsys.html

Also, there is a recipe for RGB to hex/HTML colors: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/266466

Open Geek 18 years, 8 months ago  # | flag

whoops. i'm not trying to convert anyone to python, that comment was meant for this page:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/266466

Mike Holenderski 10 years, 7 months ago  # | flag

The above code gives problems when trying to convert to the hexadecimal RGB notation (e.g. #123456) when value equals 1. Also, if saturation equals 0, then the value should be multiplied by 255, like it is for saturation greater than 0. Herewith the modified code:

proc hsv2rgb {h s v} {
  if {$s <= 0.0} {
    # achromatic
    set v [expr {int(255 * $v)}]
    return "$v $v $v"
  } else {
    set v [expr {double($v)}]
    if {$h >= 1.0} { set h 0.0 }
    set h [expr {6.0 * $h}]
    set f [expr {double($h) - int($h)}]
    set p [expr {int(255 * $v * (1.0 - $s))}]
    set q [expr {int(255 * $v * (1.0 - ($s * $f)))}]
    set t [expr {int(255 * $v * (1.0 - ($s * (1.0 - $f))))}]
    set v [expr {int(255 * $v)}]
    switch [expr {int($h)}] {
      0 { return "$v $t $p" }
      1 { return "$q $v $p" }
      2 { return "$p $v $t" }
      3 { return "$p $q $v" }
      4 { return "$t $p $v" }
      5 { return "$v $p $q" }
    }
  }
}
Created by andreas kupries on Mon, 17 Jun 2002 (MIT)
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