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watermarking, transparency problem

Posted: Sun Nov 06, 2005 12:53 pm
by josh
I have a 200 X 200 pixel watermark, and a 4,000 X 4,000 destination image. I want to copy the watermark ontop of the destination image and stretch the watermark, so I resample the watermark:

Code: Select all

$watermark = imagecreatetruecolor($width_photo_orig, $height_photo_orig);
$watermark_orig = imagecreatefrompng('watermark.png');
imageAlphaBlending($watermark_orig, false);
imageSaveAlpha($watermark_orig, true);
imagecopyresampled($watermark, $watermark_orig, 0, 0, 0, 0, $width_photo_orig, $height_photo_orig, $width_water_orig, $height_water_orig);
Problem is now the watermark is black where it should be transparent because imagecreatetruecolor creates a black image. Then the transparency was simply lost, now watermarking this image creates a black image with a watermark overriding my original photo. Is there a way for imagecreatetruecolor to produce a transparent image to start with, or for imagecopyresample to preserve transparency?

Posted: Mon Nov 07, 2005 6:47 am
by onion2k
It sounds a bit mad, but you need to set imageAlphaBlending($watermark_orig, true); rather than false, and remove the imageSaveAlpha($watermark_orig, true); line altogether.

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<?php

	$file = "wm.jpg"; // Original image to have watermark applied to it.
	$wm = "watermark.png"; // Watermark image

	$image = imagecreatefromjpeg($file);
	imagealphablending($image,true); // Tell PHP to use alpha blending when the destination image is $image
	
	$wm_image = imagecreatefrompng($wm);
	imagecopyresampled($image,$wm_image,0,0,0,0,imagesx($image),imagesy($image),imagesx($wm_image),imagesy($wm_image));

	header("Content-type: image/jpeg");
	imagejpeg($image);

?>
Obviously that code applies the watermark directly to the image instead of going via an image created with imagecreatetruecolour(). If you really need to do that I have an imagecreatetruecolortransparent() function that should do the job ..

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function imagecreatetruecolortransparent($x,$y) {
		$i = imagecreatetruecolor($x,$y);
		$b = imagecreatefromstring(base64_decode(blankpng()));
		imagealphablending($i,false);
		imagesavealpha($i,true);
		imagecopyresized($i,$b,0,0,0,0,$x,$y,imagesx($b),imagesy($b));
		return $i;
	}

	function blankpng() {

		$c  = "iVBORw0KGgoAAAANSUhEUgAAACgAAAAoCAYAAACM/rhtAAAABGdBTUEAAK/INwWK6QAAABl0RVh0U29m";
		$c .= "dHdhcmUAQWRvYmUgSW1hZ2VSZWFkeXHJZTwAAADqSURBVHjaYvz//z/DYAYAAcTEMMgBQAANegcCBNCg";
		$c .= "dyBAAA16BwIE0KB3IEAADXoHAgTQoHcgQAANegcCBNCgdyBAAA16BwIE0KB3IEAADXoHAgTQoHcgQAAN";
		$c .= "egcCBNCgdyBAAA16BwIE0KB3IEAADXoHAgTQoHcgQAANegcCBNCgdyBAAA16BwIE0KB3IEAADXoHAgTQ";
		$c .= "oHcgQAANegcCBNCgdyBAAA16BwIE0KB3IEAADXoHAgTQoHcgQAANegcCBNCgdyBAAA16BwIE0KB3IEAA";
		$c .= "DXoHAgTQoHcgQAANegcCBNCgdyBAgAEAMpcDTTQWJVEAAAAASUVORK5CYII=";

		return $c;

	}

	$image = imagecreatetruecolortransparent(200,200);
	
	header("Content-type: image/png");
	imagepng($image);

Posted: Mon Nov 07, 2005 2:56 pm
by onion2k
If you don't fancy resizing the watermark you could tile it over the image instead..

Code: Select all

<?php

	$file = "wm.jpg";
	$wm = "watermark.png";

	$image = imagecreatefromjpeg($file);
	imagealphablending($image,true);

	$wm_image = imagecreatefrompng($wm);

	imageSetTile($image,$wm_image);
	imagefilledrectangle($image,0,0,imagesx($image),imagesy($image),IMG_COLOR_TILED);

	header("Content-type: image/jpeg");
	imagejpeg($image);

?>
Sadly you can't use imagefill() unless your image is blank to start with.. coz it's a fill and only goes up to boundaries..

Re: watermarking, transparency problem

Posted: Tue Apr 24, 2012 7:36 am
by johnrishaboye
nice informative post i like it....