Pastel Colors

Keith Vetter 2003-11-06 : Picking good colors seems to be a never ending problem (see Selecting visually different RGB colors). This time I wanted random light colors as background for some black text.

The procedure Pastel below generates a random pastel color. It is based on the old X Windows tool xcolorize. It works by creating a random color in a specific region in the HSV color model.

But the results were a bit too light for my needs so I wrote the procedure LightColor which gives better results for what I need. Conceptually it works by creating a random RGB color, converting into HSV space and rejecting any color with V less than .7 (but the code is really simple). This is the same algorithm used in Named Colors to determine if the label should be in black or white.

There's a simple little demo.

 ##+##########################################################################
 #
 # pastel.tcl
 # by Keith Vetter
 #
 # Revisions:
 # KPV Nov 06, 2003 - initial revision
 #  RT Oct 18, 2004 - a button to view 12 pastels side-by-side
 #
 ##+##########################################################################
 #############################################################################

 package require Tk

 proc DoDisplay {} {
    frame .f2 -bd 2 -relief ridge
    label .f -text "W" -font {Times 48}
    label .rgb -textvariable rgb

    button .pastel -text "Pastel" -command RandomPastel
    button .light -text "Light" -command RandomLight
    button .see12 -text "P 12" -command See12Pastel
    grid .f2 .pastel
    grid ^ .light
    grid ^ .see12
    grid .f -in .f2
    grid .rgb -in .f2
    grid columnconfigure . 1 -pad 10
    RandomPastel
 }

 ##+##########################################################################
 #
 # LightColor -- returns a "light" color. A light color is one in
 # which the V value in the HSV color model is greater than .7. Since
 # the V value is simply the maximum of R,G,B we simply need at least
 # one of R,G,B must be greater than .7.
 #
 proc LightColor {} {
    set light [expr {255 * .7}]                 ;# Value threshold
    while {1} {
        set r [expr {int (255 * rand())}]
        set g [expr {int (255 * rand())}]
        set b [expr {int (255 * rand())}]
        if {$r > $light || $g > $light || $b > $light} break
    }
    return [format "\#%02x%02x%02x" $r $g $b]
 }
 ##+##########################################################################
 #
 # Pastel -- returns a "pastel" color. Code is from X Windows tool xcolorize
 # Pick "random" color in a subspace of the HSV color model and convert to RGB.
 #
 proc Pastel {} {
    set rand [expr {rand() * 262144}]
    set h [fmod $rand 360]
    set rand [expr {$rand / 359.3}]
    set s [expr {([fmod $rand 9] + 12) / 100.0}]
    set v 1

    # Convert to rgb space
    if {$h == 360} { set h 0 }
    set h [expr {$h/60}]
    set i [expr {int(floor($h))}]
    set f [expr {$h - $i}]
    set p1 [expr {$v*(1-$s)}]
    set p2 [expr {$v*(1-($s*$f))}]
    set p3 [expr {$v*(1-($s*(1-$f)))}]
    switch -- $i {
        0 { set r $v  ; set g $p3 ; set b $p1 }
        1 { set r $p2 ; set g $v  ; set b $p1 }
        2 { set r $p1 ; set g $v  ; set b $p3 }
        3 { set r $p1 ; set g $p2 ; set b $v  }
        4 { set r $p3 ; set g $p1 ; set b $v  }
        5 { set r $v  ; set g $p1 ; set b $p2 }
    }
    foreach a {r g b} { set $a [expr {int ([set $a] * 255)}] }
    return [format "\#%02x%02x%02x" $r $g $b]
 }
 proc fmod {num mod} {                           ;# Floating point modulus
    foreach {int frac} [split $num "."] break
    set frac "0.$frac"
    return [expr {($int % $mod) + $frac}]
 }

 proc RandomLight {} {
    set ::rgb [LightColor]
    .f config -bg $::rgb
 }
 proc RandomPastel {} {
    set ::rgb [Pastel]
    .f config -bg $::rgb
 }

 ##+##########################################################################
 #
 # See12Pastel - generate a list of pastels and pass to display proc
 # ShowColorLIst - show side by side list of colors with RGB labels
 #
 proc See12Pastel {} {
     for {set i 0} {$i < 12} {incr i} {
         lappend clist [Pastel]
     }
     ShowColorList $clist
 }
 proc ShowColorList {list} {
     set tl .colorlist
     if {[winfo exists $tl]} {
         eval destroy [winfo children $tl]
     } else {
         toplevel $tl
     }
     set column 0
     foreach c $list {
         grid [label $tl.lc$column -bg $c] -column $column -row 0  -sticky news
         grid [label $tl.lt$column -text $c] -column $column -row 1 
         incr column
     }
 }
 DoDisplay

uniquename 2013aug18

For the reader who does not have the time/facilities/whatever to setup the code and execute it, here are a couple of images of the windows created by the code above.

The following 'colorlist' window pops up when the 'P12' button on the main GUI above is clicked.

Category Application

Category GUI