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

<?php
/*
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);
            break;
        case IMAGETYPE_JPEG:
            $image = imagecreatefromjpeg($srcFile);
            break;
        case IMAGETYPE_PNG:
            $image = imagecreatefrompng($srcFile);
            break;
        default:
            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
    imagedestroy($newImage);

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

        // Remove the tempfile
        unlink($destFile);
        return $data;
    }

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

<?php
   //Input file
   $file = "myImage.png";
   $img = ImageCreateFromPNG($file);

   //Dimensions
   $width = imagesx($img);
   $height = imagesy($img);
   $max_width = 300;
   $max_height = 300;
   $percentage = 1;

   //Image scaling calculations
   if ( $width > $max_width ) {
      $percentage = ($height / ($width / $max_width)) > $max_height ?
           $height / $max_height :
           $width / $max_width;
   }
   elseif ( $height > $max_height) {
      $percentage = ($width / ($height / $max_height)) > $max_width ?
           $width / $max_width :
           $height / $max_height;
   }
   $new_width = $width / $percentage;
   $new_height = $height / $percentage;

   //scaled image
   $out = imagecreatetruecolor($new_width, $new_height);
   imagecopyresampled($out, $img, 0, 0, 0, 0, $new_width, $new_height, $width, $height);

   //output image
   imagepng($out);
?>