PHP resizing PNG images generate black background

Question

This is the part of the code I use to display or resize and display with Cache headers. It works fine for JPG images. But PNG images get added with black background. This type of questions are available in SO and Google but almost the solutions accepted or suggested are same: imagealphablending - FALSE and imagesavealpha - TRUE. But in my case, nothing works. What would be the problem?

$image_information=getimagesize($img);
if($image_information['mime']=='image/gif')
{
    $img=imagecreatefromgif($img);
    $type="gif";
    $image_header="image/gif";
}
elseif($image_information['mime']=='image/png')
{
    $img=imagecreatefrompng($img);
    $type="png";
    $image_header="image/png";
}
else
{
    $img=imagecreatefromjpeg($img);
    $type="jpg";
    $image_header="image/jpeg";
}

$width=imagesx($img);
$height=imagesy($img);

if((isset($w))&(!isset($h))) // If Width or Height is posted, calculate the aspect dimensions
{
    $h=($height/$width*$w);
}

if((isset($h))&(!isset($w)))
{
    $w=(($h*$width)/$height);
}

if(!isset($w))
{
    $w=$width;
}

if(!isset($h))
{
    $h=$height;
}


$new_image=imagecreatetruecolor($w, $h);

if($type=="gif")
{
    $background=imagecolorallocate($new_image, 0, 0, 0);
    // removing the black from the placeholder
    imagecolortransparent($new_image, $background); 
}
elseif($type=="png")
{
    imagealphablending($new_image, FALSE);
        imagesavealpha($new_image, TRUE);
    $transparent = imagecolorallocatealpha($new_image, 255, 255, 255, 127);
        imagefilledrectangle($new_image, 0, 0, $w, $h, $transparent);
}

imagecopyresampled($new_image,$img,0,0,0,0,$w,$h,$width,$height);
$seconds_to_cache = 864000; // Add cache headers
$ts = gmdate("D, d M Y H:i:s", time() + $seconds_to_cache) . " GMT";
header("Expires: $ts");
header("Pragma: cache");
header("Cache-Control:max-age=$seconds_to_cache, must-revalidate");
header("Last-Modified: ".gmdate("D, d M Y H:i:s", $lastModified)." GMT");


header('Content-Type: $image_header');
if($type="jpg")
imagejpeg($new_image, NULL, 75);
elseif($type=="png")
imagepng($new_image, NULL, 75);
elseif($type=="gif")
imagegif($new_image, NULL);
imagedestroy($new_image);

Edit: I saved the image to my system, tried opening in,

Picasa Photo Viewer - Image opens with Black BG.
Ms Paint - Image opens with Black BG.
Photoshop CS6 - Error message pops out: Could not open because of Program error.

Is this usefull? http://stackoverflow.com/questions/2587972/php-script-to-resize-transparent-png-images — Timvp, May 06 '14 at 18:59
To clarify, is the problem with *saving* the image through PHP or *displaying* the image on the webpage through PHP? — khaverim, May 06 '14 at 19:07
Displaying the images with PHP. When needed in multiple sizes, I use the following stricture, "images/image-name.extension/int/int" -> extension will be jpg or png or gif and first int will be width in numbers and second will be height in numbers. Wither or both the int values can be omitted. — Sarvap Praharanayuthan, May 06 '14 at 19:18

cmorrissey · Answer 1 · 2014-05-06T19:39:42.923

0

You are not saving the alpha channel from your original image.

add

imagealphablending($img, true);

right above the following code

$width=imagesx($img); $height=imagesy($img);

EDIT:

and then try this

$transparent = imagecolortransparent($new_image, imagecolorallocatealpha($new_image, 255, 255, 255, 127));
imagefill($new_image, 0, 0, $transparent);

instead of your transparent code with filled rectangle

edited May 06 '14 at 19:39

answered May 06 '14 at 19:07

cmorrissey

8,493
2
23
27

score 0 · Answer 2 · answered May 06 '14 at 19:45

0

I would suggest you use a well coded class to do image manipulation. Verot.net's php class for image upload offers, on top of the upload manipulation, all sorts of image manipulation functionalities in a DRY, well structured API. In the end, your code will be much more portable and futureproof.

answered May 06 '14 at 19:45

pixeline

17,669
12
84
109

Thank you pixeline, but I just wanted to know the reason for my code does not work. I saw similar scripts available in the Internet already. – Sarvap Praharanayuthan May 06 '14 at 19:47
OK. I would then look at what image manipulation library your specific server configuration is using. Is it GD? GD2? ImageMagick? From my experience, ImageMagick is the best and most versatile. See which is installed (phpinfo() will give you that). Otherwise, you're shooting in the dark. – pixeline May 07 '14 at 21:34

PHP resizing PNG images generate black background

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