How to Sharpen Resized WordPress Uploaded Images (jpg only)

This great snippet by Unsal Korkmaz that will sharpen resized images uploaded to wordpress (jpg only). This is a great way to fix blurry jpg thumbnail images. If you would rather use this as a plugin you can now download it from the WordPress plugin directory.

function wps_sharpen_resized_file( $resized_file ) {

    $image = wp_load_image( $resized_file );
    if ( !is_resource( $image ) )
        return new WP_Error( 'error_loading_image', $image, $file );

    $size = @getimagesize( $resized_file );
    if ( !$size )
        return new WP_Error('invalid_image', __('Could not read image size'), $file);
    list($orig_w, $orig_h, $orig_type) = $size;

    switch ( $orig_type ) {
        case IMAGETYPE_JPEG:
            $matrix = array(
                array(-1, -1, -1),
                array(-1, 16, -1),
                array(-1, -1, -1),
            );

            $divisor = array_sum(array_map('array_sum', $matrix));
            $offset   = 0; 
            imageconvolution($image, $matrix, $divisor, $offset);
            imagejpeg($image, $resized_file,apply_filters( 'jpeg_quality', 90, 'edit_image' ));
            break;
        case IMAGETYPE_PNG:
            return $resized_file;
        case IMAGETYPE_GIF:
            return $resized_file;
    }

    return $resized_file;
}   

add_filter('image_make_intermediate_size', 'wps_sharpen_resized_file',900);

Note: If this is your first time adding code snippets in WordPress, then please refer to our guide on how to properly add code snippets in WordPress, so you don’t accidentally break your site.

If you liked this code snippet, please consider checking out our other articles on the site like: 7 best WordPress GDPR plugin and how to create a job application form in WordPress.