imagecolorset
To correct m4551 at abasoft dot it example:
ImageTrueColorToPalette($im,1,$t);
might give less colors than $t, so the for loop should call "$i<ImageColorsTotal($im)" instead of "$i<$t" just to be sure, or you'll get the warning: Color index [0-9] out of range
imagecolorsforindex
(PHP 4, PHP 5)
imagecolorsforindex — Ermittelt die Farbwerte einer angegebenen Farb-Palette
Beschreibung:
array imagecolorsforindex
( resource
$im
, int $index
)
Gibt ein assoziatives Array mit Rot-, Grün- und Blau-Werten
zurück, die die Werte des Farb-Paletten-Index von
im darstellen.
Siehe auch imagecolorat() und imagecolorexact().
add a note
User Contributed Notesimagecolorsforindex
adspeed.com
24-Aug-2005 01:05
24-Aug-2005 01:05
strozek(a)deas()harvard()edu
25-Jun-2004 10:32
25-Jun-2004 10:32
Regarding m4551's method of conversion -- the actual CCIR-approved RGB-to-grayscale conversion is as follows:
grayscale component = 0.2125*R + 0.7154*G + 0.0721*B
(cf. CCIR Recommendation 709 for modern monitors)
m4551 at abasoft dot it
23-Apr-2004 06:23
23-Apr-2004 06:23
here's a function to greyscale an image even from a truecolor source (jpeg or png).
slightly poor quality, but very fast...
function imagegreyscale(&$img, $dither=1) {
if (!($t = imagecolorstotal($img))) {
$t = 256;
imagetruecolortopalette($img, $dither, $t);
}
for ($c = 0; $c < $t; $c++) {
$col = imagecolorsforindex($img, $c);
$min = min($col['red'],$col['green'],$col['blue']);
$max = max($col['red'],$col['green'],$col['blue']);
$i = ($max+$min)/2;
imagecolorset($img, $c, $i, $i, $i);
}
}