I made a progress. Here is what I have now. However, the quality is very low. Advices please.
Code: Select all
$im = imagecreatefrompng('public/images/bg-tmp.png');
$pixels = array();
for($y = 0; $y < 24; $y++)
{
for($x = 0; $x < 24; $x++)
{
$rgb = imagecolorat($im, $x, $y);
$pixels[] = array($x, $y, calc_alpha_diff(0, 0, 0, ($rgb >> 16) & 0xFF, ($rgb >> 8) & 0xFF, $rgb & 0xFF));
}
}
function calc_alpha_diff($R1,$G1,$B1,$R2,$G2,$B2)
{
$color_diff = max($R1,$R2) - min($R1,$R2) + max($G1,$G2) - min($G1,$G2) + max($B1,$B2) - min($B1,$B2);
$array = array
(
100 => 510, // 1
75 => 382, // 0.75
50 => 256, // 0.5
25 => 128, // 0.25
0 => 0 // 0
);
// find the nearest value
foreach($array as $key => $val)
{
$delta = abs($val - $color_diff);
if(!isset($min_delta) || $min_delta > $delta)
{
$min_delta = $delta;
$alpha = $key;
}
}
return $alpha;
}
$im = imagecreatetruecolor(24, 24);
foreach($pixels as $p)
{
if($p[2] != 0)
{
imagesetpixel($im, $p[0], $p[1], imagecolorallocatealpha($im, 255, 0, 0, $p[2]));
}
}
// make image transperant
imagecolortransparent($im, 0);
imagepng($im);
imagedestroy($im);
header('Content-type: image/png');
exit;