这段代码可以帮助你判断任意图片的主色调，使用了简单的统计算法实现

$i = imagecreatefromjpeg("image.jpg"); 
   
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);