How do i resize and convert an uploaded image to a PNG using GD

Mar 12, 2012   //   by   //   Blog, PHP Tutorial  //  No Comments

I want to allow users to upload avatar-type images in a variety of formats (GIF,JPEG,PNG at least), but to save them all as PNG database BLOBs. If the images are oversize, pixelwise, i want to resize them before DB-insertion.

Resizes an image and converts it to PNG returning the PNG data as a string
function imageToPng($srcFile, $maxSize = 100) {  
    list($width_orig, $height_orig, $type) = getimagesize($srcFile);        

    // Get the aspect ratio
    $ratio_orig = $width_orig / $height_orig;

    $width  = $maxSize; 
    $height = $maxSize;

    // resize to height (orig is portrait) 
    if ($ratio_orig < 1) {
        $width = $height * $ratio_orig;
    // resize to width (orig is landscape)
    else {
        $height = $width / $ratio_orig;

    // Temporarily increase the memory limit to allow for larger images
    ini_set('memory_limit', '32M'); 

    switch ($type) 
        case IMAGETYPE_GIF: 
            $image = imagecreatefromgif($srcFile); 
        case IMAGETYPE_JPEG:  
            $image = imagecreatefromjpeg($srcFile); 
        case IMAGETYPE_PNG:  
            $image = imagecreatefrompng($srcFile);
            throw new Exception('Unrecognized image type ' . $type);

    // create a new blank image
    $newImage = imagecreatetruecolor($width, $height);

    // Copy the old image to the new image
    imagecopyresampled($newImage, $image, 0, 0, 0, 0, $width, $height, $width_orig, $height_orig);

    // Output to a temp file
    $destFile = tempnam();
    imagepng($newImage, $destFile);  

    // Free memory                           

    if ( is_file($destFile) ) {
        $f = fopen($destFile, 'rb');   
        $data = fread($f);       

        // Remove the tempfile
        return $data;

    throw new Exception('Image conversion failed.');

Leave a comment

Share This Post

RSS Wordpress News

  • The Year in Review (and Resolutions for 2018) January 3, 2018
    It was quite a year for the community, and we've got a lot to look forward to.
  • Managing Your Blog On a Mobile Device December 13, 2017
    A few enhancements we've added to the iOS and Android apps for easier blogging.
  • New Premium Themes: Small Business and Photo Blog December 7, 2017
    Introducing two new premium themes: Small Business, made for your entrepreneurial endeavors, and Photo Blog, designed to make your photography shine.
  • Updated Privacy Policy December 4, 2017
    As part of our commitment to privacy and transparency, we’re updating our Privacy Policy. We want to give you more information about how we collect and use personal information — in a more organized and readable format. “Your privacy is critically important to us.” These are the first words of …
  • Update Your Avatar on October 12, 2017
    Manage, upload, and edit your profile photo at
  • A New Media Picker for the iOS WordPress App October 9, 2017
    Sometimes it’s the extra touches that make all the difference; on your website, that’s the photos and video that give your content life. You asked for streamlined access to your media library and the camera and photos on your device, to make uploading and inserting photos and videos easier. We …