I made a test on GTmetrix.com and I got a pretty bad grade regarding the Page Speed (D or F). The worse error is the following:

Serve scaled images (grade F):
some image URL is resized in HTML or CSS from 1024x539 to 530x279. Serving a scaled image could save 70.3KiB (73% reduction).

What should I do to get a better grade? How can I solve this issue? What can I do to prevent the resizing in HTML? Is it better to upload to WP smaller images? What would be the best resolution?

5 Answers 5


The best way would be to resize them before uploading them.

You could also try using this function to resize the image on the fly.

 * Resize images dynamically using wp built in functions
 * Victor Teixeira
 * php 5.2+
 * Exemplo de uso:
 * <?php 
 * $thumb = get_post_thumbnail_id(); 
 * $image = vt_resize( $thumb, '', 140, 110, true );
 * ?>
 * <img src="<?php echo $image[url]; ?>" width="<?php echo $image[width]; ?>" height="<?php echo $image[height]; ?>" />
 * @param int $attach_id
 * @param string $img_url
 * @param int $width
 * @param int $height
 * @param bool $crop
 * @return array
if ( !function_exists( 'vt_resize') ) {
    function vt_resize( $attach_id = null, $img_url = null, $width, $height, $crop = false ) {

        // this is an attachment, so we have the ID
        if ( $attach_id ) {

            $image_src = wp_get_attachment_image_src( $attach_id, 'full' );
            $file_path = get_attached_file( $attach_id );

        // this is not an attachment, let's use the image url
        } else if ( $img_url ) {

            $file_path = parse_url( $img_url );
            $file_path = $_SERVER['DOCUMENT_ROOT'] . $file_path['path'];

            // Look for Multisite Path
            if(file_exists($file_path) === false){
                global $blog_id;
                $file_path = parse_url( $img_url );
                if (preg_match("/files/", $file_path['path'])) {
                    $path = explode('/',$file_path['path']);
                    foreach($path as $k=>$v){
                        if($v == 'files'){
                            $path[$k-1] = 'wp-content/blogs.dir/'.$blog_id;
                    $path = implode('/',$path);
                $file_path = $_SERVER['DOCUMENT_ROOT'].$path;
            //$file_path = ltrim( $file_path['path'], '/' );
            //$file_path = rtrim( ABSPATH, '/' ).$file_path['path'];

            $orig_size = getimagesize( $file_path );

            $image_src[0] = $img_url;
            $image_src[1] = $orig_size[0];
            $image_src[2] = $orig_size[1];

        $file_info = pathinfo( $file_path );

        // check if file exists
        $base_file = $file_info['dirname'].'/'.$file_info['filename'].'.'.$file_info['extension'];
        if ( !file_exists($base_file) )

        $extension = '.'. $file_info['extension'];

        // the image path without the extension
        $no_ext_path = $file_info['dirname'].'/'.$file_info['filename'];

        $cropped_img_path = $no_ext_path.'-'.$width.'x'.$height.$extension;

        // checking if the file size is larger than the target size
        // if it is smaller or the same size, stop right here and return
        if ( $image_src[1] > $width ) {

            // the file is larger, check if the resized version already exists (for $crop = true but will also work for $crop = false if the sizes match)
            if ( file_exists( $cropped_img_path ) ) {

                $cropped_img_url = str_replace( basename( $image_src[0] ), basename( $cropped_img_path ), $image_src[0] );

                $vt_image = array (
                    'url' => $cropped_img_url,
                    'width' => $width,
                    'height' => $height

                return $vt_image;

            // $crop = false or no height set
            if ( $crop == false OR !$height ) {

                // calculate the size proportionaly
                $proportional_size = wp_constrain_dimensions( $image_src[1], $image_src[2], $width, $height );
                $resized_img_path = $no_ext_path.'-'.$proportional_size[0].'x'.$proportional_size[1].$extension;

                // checking if the file already exists
                if ( file_exists( $resized_img_path ) ) {

                    $resized_img_url = str_replace( basename( $image_src[0] ), basename( $resized_img_path ), $image_src[0] );

                    $vt_image = array (
                        'url' => $resized_img_url,
                        'width' => $proportional_size[0],
                        'height' => $proportional_size[1]

                    return $vt_image;

            // check if image width is smaller than set width
            $img_size = getimagesize( $file_path );
            if ( $img_size[0] <= $width ) $width = $img_size[0];

            // Check if GD Library installed
            if (!function_exists ('imagecreatetruecolor')) {
                echo 'GD Library Error: imagecreatetruecolor does not exist - please contact your webhost and ask them to install the GD library';

            // no cache files - let's finally resize it
            $new_img_path = image_resize( $file_path, $width, $height, $crop );         
            $new_img_size = getimagesize( $new_img_path );
            $new_img = str_replace( basename( $image_src[0] ), basename( $new_img_path ), $image_src[0] );

            // resized output
            $vt_image = array (
                'url' => $new_img,
                'width' => $new_img_size[0],
                'height' => $new_img_size[1]

            return $vt_image;

        // default output - without resizing
        $vt_image = array (
            'url' => $image_src[0],
            'width' => $width,
            'height' => $height

        return $vt_image;

Just put that in your theme's functions.php file. You can use it in your theme like this:

<?php $image = vt_resize(get_post_thumbnail_id(), '', 277, 115, true); ?>
    <img src="<?php echo $image[url]; ?>"  width="<?php echo $image[width]; ?>" height="<?php echo $image[height]; ?>" />

This page outlines some steps you can do to further optimize your site and is based on the recommendations by YSlow. I highly recommend W3 Total Cache and Yahoo's Smush.it plugins.



It would be better to get wordpress to create all the sizes you need when uploading in the first place. I always try to upload the highest resolution file I can..

You could use http://wordpress.org/extend/plugins/additional-image-sizes-zui/ to create images in the wordpress media library at 530x279 etc...


You can try a simple solution with a Plugin called: "Adaptive Images for WordPress" Resizes and optimizes images delivered to mobile devices, in a transparent and unobtrusive way, so that the total download time is dramatically reduced. It works as a filter between the device and your WordPress website. It actually works for all types of device screen sizes, although it is targeted mostly at mobile environments.


You can solve “serve scaled images” error by resizing the images prior to uploading. You can do it very easily and quickly by using Imsanity. Follow these steps:

  1. Install and activate the plugin.
  2. Head to Settings > Imsanity.
  3. A new page will appear. Choose your desired image size within a page or post. You can also specify the size of images uploaded directly to the Media Library, along with Theme Headers, logos and other places.
  4. For Convert PNG to JPG and BMP to JPG options, choose Yes.
  5. Finally, click on Save Changes button.

You can find more information about these steps right here.


You can use this its very useful and easy and can be compressed via front-end directly


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