thinkphp在为图片加水印的时候。如果水印图片是png图片，透明度处理很不理想，与是做以下处理
在Image.class.php中新增
static function imagecopymerge_alpha($dst_im, $src_im, $dst_x, $dst_y, $src_x, $src_y, $src_w, $src_h, $pct){
$opacity=$pct;
// getting the watermark width
$w = imagesx($src_im);
// getting the watermark height
$h = imagesy($src_im);
// creating a cut resource
$cut = imagecreatetruecolor($src_w, $src_h);
// copying that section of the background to the cut
imagecopy($cut, $dst_im, 0, 0, $dst_x, $dst_y, $src_w, $src_h);
// inverting the opacity
//$opacity = 100 - $opacity;
// placing the watermark now
imagecopy($cut, $src_im, 0, 0, $src_x, $src_y, $src_w, $src_h);
imagecopymerge($dst_im, $cut, $dst_x, $dst_y, $src_x, $src_y, $src_w, $src_h, $opacity);
}
然后在water方法中把原来的替换就ok，替换方法如下：
//生成混合图像(原来系统中的,注释掉)
//imagecopymerge($sImage, $wImage, $posX, $posY, 0, 0, $wInfo['width'], $wInfo['height'], $alpha);
//新加===================================================================
self::imagecopymerge_alpha($sImage, $wImage, $posX, $posY, 0, 0, $wInfo['width'], $wInfo['height'], $alpha);