getAvgGreyScale.php

<?php

/**
 * the image object
 * e.g. imagecreatefrompng('path/to/image.png')
 * @param $im
 * sample position of an image
 * @param $x 
 * @param $y
 *
 * @return float
 */
function getgray($im, $x, $y) {
	//获取($x, $y)处的rgb值
	$rgb  = imagecolorat($im, $x, $y);
	//计算灰度
	$red    = ($rgb >> 16) & 0xFF;
	$green    = ($rgb >> 8 ) & 0xFF;
	$blue    = $rgb & 0xFF;
	$gray = round(.299*$red + .587*$green + .114*$blue);
	return $gray;
}

/**
 * the image object
 * e.g. imagecreatefrompng('path/to/image.png')
 * @param $im
 * sampling starting/ending point
 * @param $x
 * @param $y
 * dimension of the sampling area
 * @param $width
 * @param $height
 * whether the starting/ending point
 * @param bool $end
 *
 * @return float|int
 */
function getAvgGray($im, $x, $y, $width, $height, $end=false) {
	$avggray = $gray = 0;
	if ($end) {
		//当传入的($x, $y)坐标为结束位置时 则结束位置为($x,$y)
		$x_width    = $x;
		$y_height    = $y;
		//开始位置 (结束位置 - 水印宽高)
		$x = $x - $width; $y = $y - $height;
	} else {
		$x_width    = $x+$width;
		$y_height    = $y+$height;
	}
	$index=0;
	for ($i = $x; $i <= $x_width; $i++) {
		for ($j = $y; $j <= $y_height; $j++) {
			$gray += getgray($im, $i, $j);
			print('index:'.$index.' x:'.$i.'; y:'.$j.' '.$gray.'<br>');
			$index +=1;
		}
	}
	var_dump(($width+1)*($height+1));
	$avggray = round($gray/(($width+1)*($height+1)));
	return $avggray;
}