PHP - 创建一个带有半透明徽标/水印的PNG文件

Question

I'm trying to place a logo into a white image and make it semi-transparent to be used as a watermark.

Here is my code...

   // load the stamp and the photo to apply the watermark to
   if (file_exists($logoPath)) {

      $im = imagecreatefrompng($logoPath);
      $size = getimagesize($logoPath);

      $stamp = imagecreatetruecolor(612, 792);
      imagefilledrectangle($stamp, 0, 0, 612-1, 792-1, 0xFFFFFF);
      $sx = imagesx($stamp);
      $sy = imagesy($stamp);

      // center width and height
      $centerX=$sx/2-$size[0]/2;
      $centerY=$sy/2-$size[1]/2;

      $res=imagecopymerge($stamp, $im, $centerX,$centerY, 0, 0, $sx, $sy, 15);

      $waterPath = $watermark_path.$broker_id."_watermark.png";

      // Save the image to file and free memory
      imagepng($stamp, $waterPath);
      imagedestroy($stamp);
      imagedestroy($im);
   }

It all looks good to me but when I run it I get this...

http://i43.tinypic.com/2cyft06.jpg

...as you can see, the lower right quad of the image is getting colored for some reason.

Answer 1

if you take a look at imagecopymerge() docs, the 7th and 8th arguments represent the source image width and height amount. You appear to pass the target image height (612, 792), so basically you're trying to copy a 612x792 slice from your logo image, which looks much smaller.

I'll try to better describe the arguments:

$res = imagecopymerge(
          $stamp,           // <- target image
          $im,              // <- source image, from where to copy (logo)
          $centerX,         // <- target x-position (where to place your logo), 
          $centerY,         // <- target y-position 
          0,                // <- source x-position (x-offset from where to start copy)
          0,                // <- source y-position
          imagesx($im),     // <- amount to copy from source (width)
          imagesy($im),     // <- amount... (height)
          15                // <- i have no idea what this is :)
        );