colours

By: Unknown on 00:31

Color Handling
 
For images with an 8-bit indexed palette it can be tricky to manage colors.
<?
$im = ImageCreate(300,256);
for($r=0; $r<256; $r++) {
$col = ImageColorAllocate($im,$r,0,0);
ImageLine($im, 0,$r, 100, $r, $col);
}
for($g=0; $g<256; $g++) {
$col = ImageColorAllocate($im,0,$g,0);
ImageLine($im, 100,255-$g, 200, 255-$g, $col);
}
for($b=0; $b<256; $b++) {
$col = ImageColorAllocate($im,0,0,$b);
ImageLine($im, 200,$b, 300, $b, $col);
}
Header('Content-Type: image/png');
ImagePNG($im);
?> Output:

 

For paletted images the following functions can be useful:
o ImageColorClosest
o ImageColorExact 
o ImageColorDeallocate

Colour Handling
 
For Truecolor images we have no such issues.
<?
$im = ImageCreateTruecolor(300,256);
for($r=0; $r<256; $r++) {
$col = ImageColorAllocate($im,$r,0,0);
ImageLine($im, 0,$r, 100, $r, $col);
}
for($g=0; $g<256; $g++) {
$col = ImageColorAllocate($im,0,$g,0);
ImageLine($im, 100,255-$g, 200, 255-$g, $col);
}
for($b=0; $b<256; $b++) {
$col = ImageColorAllocate($im,0,0,$b);
ImageLine($im, 200,$b, 300, $b, $col);
}
Header('Content-Type: image/png');
ImagePNG($im);
?>
Output:






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