Code Examples -> imageconvolution() does not appear in PHP with non-bundled GD libraries or a PHP version lower than 5.1. I wrote a replication of imageconvolution() in PHP.

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PHP Code Examples

Title :	imageconvolution() does not appear in PHP with non-bundled GD libraries or a PHP version lower than 5.1. I wrote a replication of imageconvolution() in PHP.
Categories :	PHP, GD image library, Graphics	Chao Xu
Date :	Mar 13th 2007
Grade :	1 of 5 (graded 1 times)
Viewed :	5632
File :	No file for this code example.
Images :	No Images for this code example.

Search :	More code by Chao Xu
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Tools :	My Examples List

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imageconvolution() does not appear in PHP with non-bundled GD libraries or a PHP version lower than 5.1.
It is a rare situation(if PHP developers are smart and use a PHP5 hosting), but it still happens. That’s why I wrote a replication of imageconvolution() in PHP, because it’s written in PHP, it is 50 times slower than the bundled version. But compare to the one listed on PHP.net’s comment by interghost at crovortex dot com, this is 30% faster and supports offset.

imageconvolution() does not appear in PHP with non-bundled GD libraries or a PHP version lower than 5.1.
It is a rare situation(if PHP developers are smart and use a PHP5 hosting), but it still happens. That’s why I wrote a replication of imageconvolution() in PHP, because it’s written in PHP, it is 50 times slower than the bundled version. But compare to the one listed on PHP.net’s comment by interghost at crovortex dot com, this is 30% faster and supports offset.

<?php
if(!function_exists(‘imageconvolution’)){
function imageconvolution($src, $filter, $filter_div, $offset){
if ($src==NULL) {
return false;
}

$sx = imagesx($src);
$sy = imagesy($src);
$srcback = ImageCreateTrueColor ($sx, $sy);
ImageCopy($srcback, $src,0,0,0,0,$sx,$sy);

if($srcback==NULL){
return 0;
}

for ($y=0; $y<$sy; ++$y){
for($x=0; $x<$sx; ++$x){
$new_r = $new_g = $new_b = 0;
$alpha = imagecolorat($srcback, $pxl[0], $pxl[1]);
$new_a = $alpha >> 24;

for ($j=0; $j<3; ++$j) {
$yv = min(max($y - 1 + $j, 0), $sy - 1);
for ($i=0; $i<3; ++$i) {
$pxl = array(min(max($x - 1 + $i, 0), $sx - 1), $yv);
$rgb = imagecolorat($srcback, $pxl[0], $pxl[1]);
$new_r += (($rgb >> 16) & 0xFF) * $filter[$j][$i];
$new_g += (($rgb >> 8) & 0xFF) * $filter[$j][$i];
$new_b += ($rgb & 0xFF) * $filter[$j][$i];
}
}

$new_r = ($new_r/$filter_div)+$offset;
$new_g = ($new_g/$filter_div)+$offset;
$new_b = ($new_b/$filter_div)+$offset;

$new_r = ($new_r > 255)? 255 : (($new_r < 0)? 0:$new_r);
$new_g = ($new_g > 255)? 255 : (($new_g < 0)? 0:$new_g);
$new_b = ($new_b > 255)? 255 : (($new_b < 0)? 0:$new_b);

$new_pxl = ImageColorAllocateAlpha($src, (int)$new_r, (int)$new_g, (int)$new_b, $new_a);
if ($new_pxl == -1) {
$new_pxl = ImageColorClosestAlpha($src, (int)$new_r, (int)$new_g, (int)$new_b, $new_a);
}
if (($y >= 0) && ($y < $sy)) {
imagesetpixel($src, $x, $y, $new_pxl);
}
}
}
imagedestroy($srcback);
return true;
}
}
?>

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