Changing PNG Transparency using PHP

bigred · 10 Jan 2008 at 20:47

Hi,

For a project I need to create a dynamically generated heatmap which is overlaid on a Google Map. This works fine, however you can no longer see the map view as it is covered by the heatmap image. Theres no methods available within the Google Map API for changing transparency/etc, however as this is a PNG image I could simple change the opacity of the overlay image.

Therefore, does anyone know of any way of changing the opacity of a (PNG) image using PHP?

Thanks,
Alex

psyr33n · 10 Jan 2008 at 21:30

imagecolortransparent() sets a designated colour to transparent, so for instance if the part of the image covering the map is white it will be:

Code:

<?php

imagecolortransparent($img, imagecolorallocate($img, 255, 255, 255));

?>

Confused · 10 Jan 2008 at 21:32

Could you not make the PNG transparent in the first place? Or am I barking up the wrong tree...?

Ross1234 · 10 Jan 2008 at 22:12

think he means completely transparent ie you cant see it at all

bigred · 10 Jan 2008 at 23:30

psyr33n said:
imagecolortransparent() sets a designated colour to transparent, so for instance if the part of the image covering the map is white it will be:

Code:

<?php imagecolortransparent($img, imagecolorallocate($img, 255, 255, 255)); ?>

Thanks, I've already done that which solves half the problem by removing the white background colour; however I need the transparency level of the rest of the image to be semi-transparent too.

This screenshot might explain things clearer (ignore the white squares, thats just for testing); http://www.dur.ac.uk/alexander.marshall/temp/screenshot.png

Augmented · 11 Jan 2008 at 00:51

Have you considered doing it with CSS/Javascript?

Mozilla etc.

Code:

img {
opacity: .5}

IE

Code:

img {
filter: alpha(opacity=50);}

http://www.quirksmode.org/css/opacity.html