<?php
$i=imagecreatefromjpeg("test.jpg");//测试图片，自己定义一个，注意路径
for ($x=0;$x<imagesx($i);$x++) {
  for ($y=0;$y<imagesy($i);$y++) {
    $rgb = imagecolorat($i,$x,$y);
    $r=($rgb >>16) & 0xFF;
    $g=($rgb >> & 0xFF;
    $b=$rgb & 0xFF;
    $rTotal += $r;
    $gTotal += $g;
    $bTotal += $b;
    $total++;
  }
}
$rAverage = round($rTotal/$total);
$gAverage = round($gTotal/$total);
$bAverage = round($bTotal/$total);
//示例：
echo $rAverage;
?>