Optimize Images on Upload for Wordpress

WP-Optimize-Image-On-Upload.php

<?php
/**
* Wordpress function to optimize image in accordance with Google Pagespeed recommendations upon 
* upload. Supports jpeg/jpg image types.
*
* Authored by: Wes Melton
* Source: https://gist.github.com/wmelton/bbf82ce43103fae7efe5946734e4de19
*
* This function compresses the image, converts it to a progressive JPEG, and strips ICC information. 
* It also converts it to sRGB colorspace, compresses to 85% quality and then saves it back.
* This ensures that photos uploaded to Wordpress are being uploaded at the correct optimization levels. Obviously
* the user needs to not upload a 4k image, as the compressed file size would still be enormous for mobiles.
*
* Original Google Recommendation: https://developers.google.com/speed/docs/insights/OptimizeImages
*
* ** I haven't battle tested this. Suggest fixes in the comments!
**/ 
function _optimize_on_upload( $obj ) {

    //Ensure the ImageMagick extension is installed.
    if( extension_loaded('imagick') || class_exists("Imagick") ){

      if( 'image' != substr( $obj['type'], 0, 5 ) )
      {
        return $obj;
      }

      $imageURL = $obj['file'];

      $pathParts = pathinfo($imageURL);

      if(strtolower( $pathParts['extension'] ) != 'jpg' && strtolower( $pathParts['extension'] ) != 'jpeg')
      {
        return $obj;
      }

      //New ImageMagick object.
      $img = new Imagick();

      $img->readImage($obj['file']);

      //Google PageSpeed requires progressive jpegs if jpeg.
      $img->setInterlaceScheme(Imagick::INTERLACE_PLANE);

      //Google requires compressions quality of 85.
      $img->setImageCompressionQuality(85);

      //Set colorspace to sRGB.
      $img->setImageColorspace(13);

      //Imagick library doesn't use the 4:2:0 pattern for chroma subsampling.
      //This is a PHP specific method of acheiving the same output.
      $img->setSamplingFactors(array('2x2', '1x1', '1x1'));

      //Strip image of ICC profiles, etc.
      $img->stripImage();

      //Save it back to the server.
      $img->writeImage();

    }

    return $obj;
}

add_filter( 'wp_handle_upload', '_optimize_on_upload' );