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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....