Edit report at http://bugs.php.net/bug.php?id=23815&edit=1
ID: 23815
Comment by: setvik at gmail dot com
Reported by: bjorn at smokingmedia dot com
Summary: imagecopymerge doesn't respect alpha-channel in PNG-24
file
Status: Assigned
Type: Feature/Change Request
Package: Feature/Change Request
Operating System: Linux pluto 2.4.18lvm-r1
PHP Version: 5.2.9
Assigned To: pajoye
New Comment:
I have the same need to merge alpha images with the opacity of the top
one
reduced, and like the others in this thread, I assumed imagecopymerge
would
respect the alpha settings in the image. Based on comments here and in
the docs
( http://php.net/manual/en/function.imagecopymerge.php), others are
making the
same assumption.
@pajoye - The inclusion of alpha support whether in imagecopymerge or an
additional function would be very valuable for working with images,
especially
watermarks with complex transparency. Any chance imagecopymerge can be
patched
to support this? Or should an additional function be written and the
documentation for imagecopymerge updated?
What's your take?
Previous Comments:
[2009-12-10 18:35:56] andre at webkr dot de
Ah, I see. It's imagecopy() which implements alpha transparency while
imagecopymerge() does not.
[2009-12-10 18:23:20] andre at webkr dot de
So what does the "it implements alpha transparency for true colour
images" in "When pct = 0, no action is taken, when 100 this function
behaves identically to imagecopy() for pallete images, while it
implements alpha transparency for true colour images." mean anyway?
[2009-07-20 12:10:43] steve at redmonkey dot org
Thanks, understood. Although, I do think it would be a useful feature,
perhaps there's scope for an 'imagecopymergealpha' type function in the
future?
[2009-07-20 08:43:04] paj...@php.net
imagecopymerge was not meant to support the alpha channel but to emulate
it via pct. It was also not meant to use both the alpha or the pct value
to blend an image over another.
[2009-07-20 05:44:49] steve at redmonkey dot org
To make life a little easier I've put the notes and examples together on
a simple web page at http://www.redmonkey.org/php-bug-23815/
After investigating the code base a little further I've realised my
patch solution can be made more efficient as there is no need to make a
copy of the source or pass the image over to gdImageCopy once the new
alpha level has been set as we've already done the all the work and can
simply set the pixels RGBA index within the second image scan.
The revised patch (which is also available from a link on the web page)
is as follows
--- php-5.3.0/ext/gd/libgd/gd.c 2009-05-27 08:17:54.0 +0100
+++ php-5.3.0-build/ext/gd/libgd/gd.c 2009-07-20 05:54:21.709936176
+0100
@@ -2255,6 +2255,67 @@
int ncR, ncG, ncB;
toy = dstY;
+ if (pct == 100) {
+ /* no opacity adjustment required pass through to gdImageCopy()
*/
+ gdImageCopy(dst, src, dstX, dstY, srcX, srcY, w, h);
+ return;
+ }
+
+ if (pct == 0) {
+ /* 0% opacity? nothing needs to be done */
+ return;
+ }
+
+ if (src->trueColor && dst->trueColor) {
+ /* support for maintaining the alpha (transparency) of both
source
and
+* destination images (assuming they are true colour) while
opacity
blending.
+*/
+ int ca, cr, cg, cb;
+ float na;
+ float ac;
+
+ /* we need to loop through the src image to get the max
transparency
level */
+ int mt = 0;
+
+ for (y = 0; y < h; y++) {
+ for (x = 0; x < w; x++) {
+ c = gdImageGetTrueColorPixel (src, srcX + x,
srcY + y);
+ ca = gdImageAlpha(src, c);
+
+ mt = ca > mt ? ca : mt;
+ }
+ }
+
+ /* src has no transparency? set to use full alpha range */
+ mt = mt == gdAlphaOpaque ? gdAlphaMax : mt;
+
+ /* alpha correction factor */
+ ac = (float)mt / gdAlphaMax;
+
+ /* loop through the image again and set/adjust alpha channel
level
*/
+ for (y = 0; y <
