PHP 對 png 圖像進行縮放，支持透明背景

function smart_resize_image( $file, $width = 0, $height = 0, $proportional = false, $output = 'file', $delete_original = true, $use_linux_commands = false )
    {
        if ( $height <= 0 && $width <= 0 ) {
            return false;
        }
        $info = getimagesize($file);
        $image = '';


    $final_width = 0;
    $final_height = 0;
    list($width_old, $height_old) = $info;

    if ($proportional) {
        if ($width == 0) $factor = $height/$height_old;
        elseif ($height == 0) $factor = $width/$width_old;
        else $factor = min ( $width / $width_old, $height / $height_old);  
        $final_width = round ($width_old * $factor);
        $final_height = round ($height_old * $factor);

    }
    else {       
        $final_width = ( $width <= 0 ) ? $width_old : $width;
        $final_height = ( $height <= 0 ) ? $height_old : $height;
    }

    switch ($info[2] ) {
        case IMAGETYPE_GIF:
            $image = imagecreatefromgif($file);
        break;
        case IMAGETYPE_JPEG:
            $image = imagecreatefromjpeg($file);
        break;
        case IMAGETYPE_PNG:
            $image = imagecreatefrompng($file);
        break;
        default:
            return false;
    }

    $image_resized = imagecreatetruecolor( $final_width, $final_height );

    if ( ($info[2] == IMAGETYPE_GIF) || ($info[2] == IMAGETYPE_PNG) ) {
        $trnprt_indx = imagecolortransparent($image);
        // If we have a specific transparent color
        if ($trnprt_indx >= 0) {
            // Get the original image's transparent color's RGB values
            $trnprt_color    = imagecolorsforindex($image, $trnprt_indx);
            // Allocate the same color in the new image resource
            $trnprt_indx    = imagecolorallocate($image_resized, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);
            // Completely fill the background of the new image with allocated color.
            imagefill($image_resized, 0, 0, $trnprt_indx);
            // Set the background color for new image to transparent
            imagecolortransparent($image_resized, $trnprt_indx);
        }
        // Always make a transparent background color for PNGs that don't have one allocated already
        elseif ($info[2] == IMAGETYPE_PNG) {
            // Turn off transparency blending (temporarily)
            imagealphablending($image_resized, false);
            // Create a new transparent color for image
            $color = imagecolorallocatealpha($image_resized, 0, 0, 0, 127);

            // Completely fill the background of the new image with allocated color.
            imagefill($image_resized, 0, 0, $color);

            // Restore transparency blending
            imagesavealpha($image_resized, true);
        }
    }

    imagecopyresampled($image_resized, $image, 0, 0, 0, 0, $final_width, $final_height, $width_old, $height_old);

    if ( $delete_original ) {
        if ( $use_linux_commands )
            exec('rm '.$file);
        else
            @unlink($file);
    }

    switch ( strtolower($output) ) {
        case 'browser':
            $mime = image_type_to_mime_type($info[2]);
            header("Content-type: $mime");
            $output = NULL;
        break;
        case 'file':
            $output = $file;
        break;
        case 'return':
            return $image_resized;
        break;
        default:
        break;
    }

    switch ($info[2] ) {
        case IMAGETYPE_GIF:
            imagegif($image_resized, $output);
        break;
        case IMAGETYPE_JPEG:
            imagejpeg($image_resized, $output);
        break;
        case IMAGETYPE_PNG:
            imagepng($image_resized, $output);
        break;
        default:
            return false;
    }

    return true;
}</pre>