Blurring image using WordPress

functions.php

/**
 * Several functions relatting to blurring images on uploaded.
 * @see https://codeable.io/community/how-to-watermark-wordpress-images-with-imagemagick/
 */ 
    add_image_size( 'background-image-blurred', 1920, 1080, true );

    function generate_blurred_image( $meta ) {

      $time = substr( $meta['file'], 0, 7); // Extract the date in form "2015/04"
      $upload_dir = wp_upload_dir( $time ); // Get the "proper" upload dir
      
      if( isset($meta['sizes']['background-image-blurred']['file']) ) {
          $filename = $meta['sizes']['background-image-blurred']['file'];
          $meta['sizes']['background-image-blurred']['file'] = blur_image( $filename, $upload_dir );          
      }

      return $meta;

    }

    function blur_image( $filename, $upload_dir ) {

      $original_image_path = trailingslashit( $upload_dir['path'] ) . $filename;

      $image_resource = new Imagick( $original_image_path );
      $image_resource->gaussianBlurImage( 10, 100 ); // See: http://phpimagick.com/Imagick/gaussianBlurImage

      return save_blurred_image( $image_resource, $original_image_path );

    }    

    function save_blurred_image( $image_resource, $original_image_path ) {

      $image_data = pathinfo( $original_image_path );

      $new_filename = $image_data['filename'] . '-blurred.' . $image_data['extension'];

      // Build path to new blurred image
      $blurred_image_path = str_replace($image_data['basename'], $new_filename, $original_image_path);

      if ( ! $image_resource->writeImage( $blurred_image_path ) ) {
        return $image_data['basename'];          
      }

      // Delete the placeholder image WordPress made now that it's been blurred
      unlink( $original_image_path );

      return $new_filename;

    }   
    add_filter( 'wp_generate_attachment_metadata', 'generate_blurred_image' );    
     

    function force_add_size( $metadata, $id ){
    
        $upload_dir = wp_upload_dir();
        $filename = $upload_dir['basedir'].'/'.$metadata['file'];
        $extension = strtolower(strrchr($metadata['file'], '.'));
        $newfilename = str_replace($extension, '-blurred', $filename).$extension;
    
    
        $image_resource = new Imagick( $filename);
        $image_resource->gaussianBlurImage( 10, 100 ); // See: http://phpimagick.com/Imagick/gaussianBlurImage        
        $image_resource->writeImage( $newfilename );
                
        /*
        $image_resource->resizeImage(1920, 1080, Imagick::FILTER_GAUSSIAN, 70); // http://www.dylanbeattie.net/magick/filters/result.html
        $image_resource->writeImage( $newfilename );
        */
    
        //unlink( $filename );
        //delete original image altogether ---> you might want to update the post meta on this '_wp_attached_file' , you can actually get the attachment id from the filter, i have added it above. It would be best to have a actual image url in there! something like $sfile= str_replace($upload_dir['basedir'],'', $newfilename); update_post_meta($id, '_wp_attached_file', $sfile );        
    
        switch($extension){
            case '.jpg':
            case '.jpeg':
                $type = 'image/jpeg';
                break;
            case '.gif':
                $type = 'image/gif';
                break;
            case '.png':
                $type = 'image/png';
                break;
            default:
                $type = 'image/jpeg';
                break;
        } 
    
        $metadata['sizes']['background-image-blurred']= array(
            "file"=> $newfilename,
            "width"=> 1920,
            "height"=> 1080,
            "mime-type"=> $type 
        );
    
        return $metadata;
    }
    add_filter('wp_generate_attachment_metadata', 'force_add_size', 100, 2);