Question

Well I have a small problem. My script goes through a directory based on url query. While doing this it creates thumbnails for those images. Now the problem is that it creates PNG thumbnails but instead of transparent or at-least white background it puts in standard black.

Here is the code can any one point out my issue in the code, or possibly something I may have missed

<?php

$folder = $_GET['folder']; //POST if from form, GET if from URL
$thisdir = getcwd();
if(!file_exists($thisdir ."/"."$folder/thumbs")) {
    mkdir($thisdir ."/"."$folder/thumbs" , 0777);
}

function returnimages($dirname="") {

    $pattern="(\.jpg$)|(\.png$)|(\.jpeg$)|(\.gif$)"; //valid image extensions
    $handle  = opendir($dirname);
    while(false !== ($filename = readdir($handle))) {
        if(eregi($pattern, $filename)){ //if this file is a valid image
            $files[] = $filename;
        }
    }
    if (count($files)<>0) {
        sort($files);
    }

    $curimage=0;

    while($curimage !== count($files)){
        $cropfile=$dirname.'/'.$files[$curimage];echo '<br>'.$cropfile;

         if(preg_match('/[.](jpg)|(jpeg)$/', $cropfile)) {
             $source_img = imagecreatefromjpeg($cropfile);
         } elseif(preg_match('/[.](png)$/', $cropfile)) {
             imagealphablending($source_img, false);
             imagesavealpha($source_img, true);
             $source_img = imagecreatefrompng($cropfile);
         } elseif(preg_match('/[.](gif)$/', $cropfile)) {
             $source_img = imagecreatefromgif($cropfile);
         } else {
             echo "Code 43: Unable to read file type.";
             exit(0);
         }

        if (!$source_img) {
            echo "could not create image handle";
            exit(0);
        }
        $new_w = 480;
        $new_h = 480;

        $orig_w = imagesx($source_img);
        $orig_h = imagesy($source_img);

        $w_ratio = ($new_w / $orig_w);
        $h_ratio = ($new_h / $orig_h);

        if ($orig_w > $orig_h ) {//landscape from here new
            $crop_w = round($orig_w * $h_ratio);
            $crop_h = $new_h;
            $src_x = ceil( ( $orig_w - $orig_h ) / 2 );
            $src_y = 0;
        } elseif ($orig_w < $orig_h ) {//portrait
            $crop_h = round($orig_h * $w_ratio);
            $crop_w = $new_w;
            $src_x = 0;
            $src_y = ceil( ( $orig_h - $orig_w ) / 2 );
        } else {//square
            $crop_w = $new_w;
            $crop_h = $new_h;
            $src_x = 0;
            $src_y = 0;
        }
        $dest_img = imagecreatetruecolor($new_w,$new_h);
        imagecopyresampled($dest_img, $source_img, 0 , 0 , $src_x, $src_y, $crop_w, $crop_h, $orig_w, $orig_h); //till here
        if(imagejpeg($dest_img, $dirname."/thumbs/".$files[$curimage], 80)) {
            imagedestroy($dest_img);
            imagedestroy($source_img);
        } else {
            echo "could not make thumbnail image";
            exit(0);
        }
        $curimage++;
    }
}
returnimages($name=$folder);

?>

Answer 1

This is because you’re using imagejpeg as an output function for every possible type of images. I changed your code in a while loop to make it work:

// Add these defines somewhere at the top
define('TYPE_JPEG', 0);
define('TYPE_PNG', 1);
define('TYPE_GIF', 2);

// ... skipping some code. Here goes while loop iterating over every image
while($curimage !== count($files)){
    $cropfile=$dirname.'/'.$files[$curimage];echo '<br>'.$cropfile;

     // Determine type of the image
     if(preg_match('/[.](jpg)|(jpeg)$/', $cropfile)) {
         $source_img = imagecreatefromjpeg($cropfile);
         $type = TYPE_JPEG;
     } elseif(preg_match('/[.](png)$/', $cropfile)) {
         $source_img = imagecreatefrompng($cropfile);
         $type = TYPE_PNG;
     } elseif(preg_match('/[.](gif)$/', $cropfile)) {
         $source_img = imagecreatefromgif($cropfile);
         $type = TYPE_GIF;
     } else {
         echo "Code 43: Unable to read file type.";
         exit(0);
     }

    if (!$source_img) {
        echo "could not create image handle";
        exit(0);
    }
    $new_w = 480;
    $new_h = 480;

    $orig_w = imagesx($source_img);
    $orig_h = imagesy($source_img);

    $w_ratio = ($new_w / $orig_w);
    $h_ratio = ($new_h / $orig_h);

    if ($orig_w > $orig_h ) {//landscape from here new
        $crop_w = round($orig_w * $h_ratio);
        $crop_h = $new_h;
        $src_x = ceil( ( $orig_w - $orig_h ) / 2 );
        $src_y = 0;
    } elseif ($orig_w < $orig_h ) {//portrait
        $crop_h = round($orig_h * $w_ratio);
        $crop_w = $new_w;
        $src_x = 0;
        $src_y = ceil( ( $orig_h - $orig_w ) / 2 );
    } else {//square
        $crop_w = $new_w;
        $crop_h = $new_h;
        $src_x = 0;
        $src_y = 0;
    }
    $dest_img = imagecreatetruecolor($new_w,$new_h);
    $dest_path = $dirname."/thumbs/".$files[$curimage];
    switch ($type) {
        case TYPE_JPEG:
            imagecopyresampled($dest_img, $source_img, 0 , 0 , $src_x, $src_y, $crop_w, $crop_h, $orig_w, $orig_h);
            $success = imagejpeg($dest_img, $dest_path, 80);
            break;

        case TYPE_PNG:
            // Preserve alpha
            imagesavealpha($dest_img, true);
            // Create transparent color
            $color = imagecolorallocatealpha($dest_img, 0, 0, 0, 127);
            // Fill in background
            imagefill($dest_img, 0, 0, $color);
            // Copy from source
            imagecopyresampled($dest_img, $source_img, 0 , 0 , $src_x, $src_y, $crop_w, $crop_h, $orig_w, $orig_h);
            $success = imagepng($dest_img, $dest_path);
            break;

        default:
            $black = imagecolorallocate($dest_img, 0, 0, 0);
            // This will make the background transparent
            imagecolortransparent($dest_img, $black);
            // Copy from source
            imagecopyresampled($dest_img, $source_img, 0 , 0 , $src_x, $src_y, $crop_w, $crop_h, $orig_w, $orig_h);
            $success = imagegif($dest_img, $dest_path);
            break;
    }
    if($success) {
        imagedestroy($dest_img);
        imagedestroy($source_img);
    } else {
        echo "could not make thumbnail image";
        exit(0);
    }
    $curimage++;
}

As you can see, depending on the filetype we’re using different output functions: imagejpeg, imagepng and imagegif. PNG and GIF files require some extra actions in order to preserve transparency. I’ve tested it on PHP 5.2.13 under Windows using JPEG, GIF and PNG (transparent and regular) files and seems like everything is working. You can tweak additional parameters, for example imagepng takes optional $quality and $filters parameters.

Also, regarding the code:

• The most important rule: do not trust user input. You’re creating directories depending on the value of $_GET, this may be unsafe, because user can pass something like ‘/../../../../etc’
• Some cleanup won’t hurt. Use foreach instead of while with loop counter. I think glob can retrieve list of files. And returnimages($name=$folder); call doesn’t make sense to me. Do you really need to assign and call in one line?