Image transparency in imagepng() and imagegif()

2
votes

I want to resize 2 types of images (png, gif) with transparent background...

  1. But in png it works well in big size of the original image. eg. Original file dimension is 150x150 enter image description here

    change into 200x200 or exceeding the original size it works well. but in 100x100 it displays enter image description here

  2. Then the last GIF it doesn't work.

    Here my code for png

    $new_img = imagecreatetruecolor($max_w, $max_h);

    imagealphablending($new_img, false);
    imagesavealpha($new_img, true);

    $transparentindex = imagecolorallocatealpha($new_img, 255, 255, 255, 127);

    imagefill($new_img, 0, 0, $transparentindex);

    imagepng($new_img, $dir);

    Here my code for gif

    imagegif($new_img, $dir);
2
phpimage
How do you get a JPEG with a transparent background? That is not possible! Do you really mean you are resizing the images - or that you want to simply overlay them onto a bigger, transparent background? – Mark Setchell
sorry. i only need png and gif. It's my fault. – White Marcus
yes i want to resizing the images either bigger or smaller. in png bigger works fine. but smaller works with the error. then the other end gif totally not works. – White Marcus

2 Answers

2
votes

I know no PHP, but this seems to do the trick:

#!/usr/local/bin/php -f
<?php
    $neww=100;
    $newh=100;

    // Load original image and get its dimensions
    $img = imagecreatefrompng("badge.png");
    $w=imagesx($img);
    $h=imagesy($img);

    // Create output image, and fill with lots of transparency
    $out = imagecreatetruecolor($neww,$newh);
    imagealphablending($out,false);
    $transparentindex = imagecolorallocatealpha($out,0,0,0,127);
    imagefill($out,0,0,$transparentindex);
    imagesavealpha($out, true);

    // Copy original image, reized on top
    imagecopyresized($out,$img,0,0,0,0,$neww,$newh,$w,$h);
    imagepng($out,"out.png");
?>
2
votes

Here is a little hack :) Don't have any other ideas.

It involves a second image (1x1 trasparent gif)

  1. create image
  2. resize
  3. create a transparent background with same size as resized image
  4. use imagecolortransparent() to get the rgb index
  5. imagecopymerge() images
  6. voilà

.

$dir = 'http://i.stack.imgur.com/DbhrJ.png';
$max_w = 50;
$max_h = 50;

// get image size
list($src_w, $src_h) = getimagesize($dir);

if ($src_w > $max_w) {
    $ratio = $max_w / $src_w;
    $max_w = $src_w * $ratio;
}
else if ($src_h > $max_h) {
    $ratio = $max_h / $src_h;
    $max_h = $src_h * $ratio;
}

// resize image to $max_w and $max_h, and also save alpha
$src = imagecreatefromstring(file_get_contents($dir));
$new_img = imagecreatetruecolor($max_w, $max_h);
imagealphablending($new_img, false);
imagesavealpha($new_img, true);
imagecopyresampled($new_img, $src, 0, 0, 0, 0, $max_w, $max_h, $src_w, $src_h);

// create a new image with $max_w and $max_h
$maxsize = imagecreatetruecolor($max_w, $max_h);

// add 1x1 gif and resize, then copy over $maxsize
$background = imagecreatefromgif("http://i.imgur.com/atRjCdk.gif"); // transparent 1x1 gif
imagecopyresampled($maxsize, $background, 0, 0, 0, 0, $max_w, $max_h, 1, 1);

// allocate transparency
$transparent = imagecolortransparent($maxsize);
$transparent_index = imagecolorallocate($maxsize, $transparent['red'], $transparent['green'], $transparent['blue']);
imagecolortransparent($maxsize, $transparent_index);

// image copy
imagecopymerge($maxsize, $new_img, 0, 0, 0, 0, $max_w, $max_h, 100);

// save or output
imagegif($maxsize, $path_to_save);

// destroy images
imagedestroy($maxsize);
imagedestroy($new_img);
imagedestroy($background);
imagedestroy($src);