Richard Suchenwirth 2004-08-18 - This routine takes a photo image and creates a new one, in which pixels whose color (an {r g b} list) is contained in a list of wanted colors are left unchanged; other pixels are set to the specified background colour. Additionally, you can specify a "dropout" color: pixels in this color are changed to the previous pixel's color (wanted or background) - that was helpful to filter out meridians from a timezone map. The filtered image handle is returned.
proc image'filter {img bg colors {dropout ""}} {
set w [image width $img]
set h [image height $img]
set res [image create photo -width $w -height $h]
for {set row 0} {$row<$h} {incr row} {
set outrow {}
set last $bg
for {set col 0} {$col<$w} {incr col} {
set rgb [$img get $col $row]
if {$rgb eq $dropout} {set rgb $last}
if {[lsearch -exact $colors $rgb]>=0} {
lappend outrow [rgb2color $rgb]
set last $rgb
} else {
lappend outrow $bg
set last $bg
}
}
$res put [list $outrow] -to 0 $row [expr {$w-1}] [expr {$row+1}]
}
set res
}
proc rgb2color rgb {
foreach {r g b} $rgb break
format #%02X%02X%02X $r $g $b
}