Gaussian blur with image convolution

Question

I've been trying to blur some text for a while now using the following code in PHP:

$image = imagecreate(150,25);
$background = ImageColorAllocate($image, 255, 255, 255);
$foreground = ImageColorAllocate($image, 0, 0, 0);

ImageColorTransparent($image, $background);
ImageInterlace($image, false);

ImageTTFText($image, 20, 0, 0, 20, $foreground, "font.ttf", "some text");

$gaussian = array(array(1.0, 2.0, 1.0), array(2.0, 4.0, 2.0), array(1.0, 2.0, 1.0));
imageconvolution($image, $gaussian, 16, 0);

imagePNG($image)

However the image does not blur, it only decreases in resolution, becoming grainy... Demo here..

Something tells me the resulting colors (grey, somewhere in between black and white) are not automatically allocated by `imageconvolution`. The reason you get a black and white result is because it picks the most similar colors to the blurred pixel values. Try creating the image with [`imagecreatetruecolor`](http://www.php.net/manual/en/function.imagecreatetruecolor.php). (I commented instead of answered because I'm not sure and I'm not in the position to test from here.) — TaZ, Oct 29 '12 at 00:11

score 2 · Accepted Answer · answered Oct 29 '12 at 00:14

Remove ImageColorTransparent($image, $background); to see the effect

Example

$image = imagecreate(150,25);
$background = ImageColorAllocate($image, 255, 255, 255);
$foreground = ImageColorAllocate($image, 0, 0, 0);

ImageInterlace($image, false);
ImageTTFText($image, 20, 0, 0, 20, $foreground, "verdana.ttf", "some text");

$gaussian = array(array(1.0,2.0,1.0),array(2.0,4.0,2.0),array(1.0,2.0,1.0));
imageconvolution($image, $gaussian, 16, 0);

header('Content-Type: image/png');
imagepng($image, null, 9);

Output

enter image description here

 ^ Before ^           ^ After ^

Is it possible to control the amount of blur? – Tony Bogdanov Jun 24 '13 at 20:04 — Tony Bogdanov, Jun 24 '13 at 20:04

Gaussian blur with image convolution

1 Answers1