Add transparent watermark into image

Question

I need to add transparent watermark (transparency in final image - 80%). I created this function to handle it:

function ImageAddWatermark($im, $stamp, $onLeft, $onTop, $margin){       
        // $stamp = imagecreatformpng(...) -> GD resource?
        // not important part - it calculates position of watermark 
        if($onLeft){
            $orgX = $margin;
        } else {
            $orgX = imagesx($im)-$margin-imagesx($stamp);
        }

        if($onTop){
            $orgY = $margin;
        }else {
            $orgY = imagesy($im)-$margin-imagesy($stamp);
        }

        imagecopymerge($im, $stamp, $orgX, $orgY, 0, 0, imagesx($stamp), imagesy($stamp), 50);

        return $im;
    }

Result of function: error

But imagecopymerge returns black background instead of transparent. I even heard some opinions, that imagecopymerge isn't exactly the right thing for creating transparent watermarks...

So the question is: "How can I add a transparent watermark (using alpha?) in jpeg photo?" How can I get rid of that black backgound? (In original PNG file is transparent)

what is `$stamp` before you call this function? is it a GD resource? how have you loaded it? — cmorrissey, Feb 18 '14 at 17:18
@cmorrissey if GD resource is "imagecreatefrompng(...)" and of course I call it — tomascapek, Feb 18 '14 at 17:20
add `imagealphablending($stamp, true);` after you call `imagecreatefrompng(...)` — cmorrissey, Feb 18 '14 at 17:22
possible duplicate of [imagecreatefrompng() Makes a black background instead of transparent?](http://stackoverflow.com/questions/2611852/imagecreatefrompng-makes-a-black-background-instead-of-transparent) — Marc B, Feb 18 '14 at 17:25

score 2 · Accepted Answer · edited Feb 07 '19 at 03:11

Well, I found the solution:

function ImageAddWatermark($im, $stamp, $onLeft, $onTop, $margin){

    if($onLeft){
        $orgX = $margin;
    } else {
        $orgX = imagesx($im)-$margin-imagesx($stamp);
    }

    if($onTop){
        $orgY = $margin;
    }else {
        $orgY = imagesy($im)-$margin-imagesy($stamp);
    }

    // creating a cut resource 
    $cut = imagecreatetruecolor(imagesx($stamp), imagesy($stamp)); 

    // copying relevant section from background to the cut resource 
    imagecopy($cut, $im, 0, 0, $orgX, $orgY, imagesx($stamp), imagesy($stamp)); 

    // copying relevant section from watermark to the cut resource 
    imagecopy($cut, $stamp, 0, 0, 0, 0, imagesx($stamp), imagesy($stamp)); 

    // insert cut resource to destination image 
    imagecopymerge($im, $cut, $orgX, $orgY, 0, 0, imagesx($stamp), imagesy($stamp), 50); 

    return $im;
}

Add transparent watermark into image

1 Answers1