Updated 2010-06-23 17:46:03 by AKgnome

ulis A proc to display or export the colors [histogram] of a photo image.


Why? edit

I was interested to compare the histogram of a reduced image with the histogram of the original image.

How it does? edit

The proc counts the occurrence of each color component (RGB) for all of the image colors.

Proc edit

namespace eval ::histo {
    namespace export histo

    package require Tk

    proc histo {image {cmd -display}} {
        # get options
        switch -glob -- $cmd {
            -dis*   { set cmd -display }
            -exp*   { set cmd -export }
            default {
                error "use\n\t[histo image ?-display|-export?"
            }
        }
        # get the image size
        set width [image width $image]
        set height [image height $image]
        if {$width * $height == 0} {
            error "bad image"
        }
        # count colors components
        for {set i 0} {$i < 256} {incr i} {
            foreach c {r g b} {
                set counts($c:$i) 0
            }
        }
        set max 0
        for {set y 0} {$y < $height} {incr y} {
            for {set x 0} {$x < $width} {incr x} {
                foreach {r g b} [$image get $x $y] break
                foreach c {r g b} {
                    set n [incr counts($c:[set $c])]
                    if {$max < $n} {
                        set max $n
                    }
                }
            }
        }
        if {$cmd == "-display"} {
            # display
            # compute the coef
            set coef [expr {256.0 / $max}]
            # create toplevel
            set t _$image
            toplevel .$t
            wm title .$t $image
            # draw the histogram
            set c .$t.c
            canvas $c -width [expr {256 * 3 + 40}] -height [expr {256 + 40}]
            set x0 9
            set y0 267
            $c create rectangle $x0 9 [incr x0 258] $y0 \
                    -outline black -fill white
            incr x0 8
            $c create rectangle $x0 9 [incr x0 258] $y0 \
                    -outline black -fill white
            incr x0 8
            $c create rectangle $x0 9 [incr x0 258] $y0 \
                    -outline black -fill white
            set y1 272
            set x0 10
            for {set i 0} {$i < 17} {incr i} {
                $c create line $x0 $y0 $x0 $y1
                incr x0 16
            }
            set x0 276
            for {set i 0} {$i < 17} {incr i} {
                $c create line $x0 $y0 $x0 $y1
                incr x0 16
            }
            set x0 542
            for {set i 0} {$i < 17} {incr i} {
                $c create line $x0 $y0 $x0 $y1
                incr x0 16
            }
            incr y0 -1
            set xr 10
            set xg 276
            set xb 542
            for {set i 0} {$i < 256} {incr i} {
                    set yr [expr {10 + 256 - round($counts(r:$i) * $coef)}]
                set yg [expr {10 + 256 - round($counts(g:$i) * $coef)}]
                set yb [expr {10 + 256 - round($counts(b:$i) * $coef)}]
                $c create line $xr $y0 $xr $yr -fill red
                $c create line $xg $y0 $xg $yg -fill green
                $c create line $xb $y0 $xb $yb -fill blue
                incr xr; incr xg; incr xb
            }
            $c create text 10 276 -anchor nw \
                    -text "image: $image, max count: $max"
            pack $c
        } else {
            # export
            for {set i 0} {$i < 256} {incr i} {
                foreach c {r g b} {
                    lappend list$c $counts($c:$i)
                }
            }
            return [list $listr $listg $listb]
        }
    }
}

Demo edit

# example
# -----------
# to download the image:
# http://perso.wanadoo.fr/maurice.ulis/tcl/image1.png

package require Tk
package require Img
wm withdraw .
namespace import ::histo::histo
histo [image create photo -file image1.png]

See also