Реализация алгоритма определения яркости изображения на языке PHP

<?php
 
/* Image brightness calculation class.
** Author Rampa.
** Complette 15 August 2015 in 13:00.
*/
 
class image_brightness_calculation_class {
    
    # For gif images call it.
    function get_brightness_gif($input_file) {
 
        return $this->get_brightness(imagecreatefromgif($input_file));
    }
 
    # For jpeg/jpg images call it.
    function get_brightness_jpeg($input_file) {
 
        return $this->get_brightness(imagecreatefromjpeg($input_file));
    }
 
    # For png images call it.
    function get_brightness_png($input_file) {
        
        return $this->get_brightness(imagecreatefrompng($input_file));
    }
 
    # Main image brightness calculation method.
    function get_brightness($opened_image_resource) {
        
        # Get image dimensions.
        $image_width = imagesx($opened_image_resource);
        $image_height = imagesy($opened_image_resource);
 
        # Get all pseudo brightness level.
        $image_brightness_level = $image_width*$image_height*255*3;
 
        # Counter for current brightness level.
        $image_brightness_current_level = 0;
 
        # See vertical lines,
        for( $y = 0; $y < $image_height; $y ++ ) {
            
            # and see horisontal lines of image.
            for( $x = 0; $x < $image_width; $x ++ ) {
 
                # Get image palette color index.
                $palette_color_index = imagecolorat($opened_image_resource, $x, $y);
                
                # Convert is to rgb data.
                $palette_color_rgb = imagecolorsforindex($opened_image_resource, $palette_color_index);
 
                # Increment current brightness counter.
                $image_brightness_current_level += $palette_color_rgb['red'] + $palette_color_rgb['green'] + $palette_color_rgb['blue'];
            }
        }
        
        # Get one pseudo brightness-level.
        $image_brightness_level_proportion = 100/$image_brightness_level;
 
        # Get current relative image brightness level.
        $image_brightness = round($image_brightness_current_level*$image_brightness_level_proportion, 2);
 
        # Complette.
        return $image_brightness;
        
    }
} ?>