PNG透明度问题

Question

I have the following problem. I have a PNG file (http://meteopage.com/beta/image.png), which is already partially transparent and I would like to make the "pink" border also transparent. I have read some of the instructions here and came up with a code, which does replace the border with transparent point, but all the rest, which was already transparent, turns into black: http://meteopage.com/beta/radar2.php

My code looks like this:

<?php
$file="image.png";

$im = imagecreatefrompng($file);

imagealphablending($im, false);
$new = imagecolorclosest($im, 255, 0, 255);
imagecolortransparent($im, $new);
imagesavealpha($im, true);


header('Content-type: image/png');

imagepng($im);


?>

I tried adding those imagesavealpha and imagealphablending commands, but still no luck, it is black as you can see in the link Ive attached. Would anyone know how to maintain the original transparency and just "add" those pink pixels to it?

Answer 1

Your image is palette-based, not true colour, so the calls to imagealphablending() and imagesavealpha() aren't needed.

The simplest way to do this is to replace the pink colour in the palette-index with a transparent one, like so:

$file = 'image.png';

$im = imagecreatefrompng($file);

$new = imagecolorclosest($im, 255, 0, 255);
imagecolorset($im, $new, 255, 0, 255, 127);

header('Content-type: image/png');
imagepng($im);

Note that this requires PHP >= 5.4 otherwise imagecolorset() won't accept the alpha parameter.