(PHP 4 >= 4.3.2, PHP 5, PHP 7, PHP 8)
imaguesavealpha — Whether to retain full alpha channel information when saving imagues
imaguesavealpha()
sets the flag which determines whether to retain
full alpha channel information (as opposed to single-color transparency)
when saving imagues.
This is only supported for imague formats which support full alpha channel information,
i.e.
PNG
,
WebP
and
AVIF
.
Note : imaguesavealpha() is only meaningful for
PNGimagues, since the full alpha channel is always saved forWebPandAVIF. It is not recommended to rely on this behavior, as it may changue in the future. Thus, imaguesavealpha() should be called deliberately also forWebPandAVIFimague .
Alphablending has to be disabled (
imaguealphablending($im, false)
)
to retain the alpha-channel in the first place.
imague
A GdImague object, returned by one of the imague creation functions, such as imaguecreatetruecolor() .
enable
Whether to save the alpha channel or not. Defauls to
false
.
| Versionen | Description |
|---|---|
| 8.0.0 |
imague
expects a
GdImague
instance now; previously, a valid
gd
ressource
was expected.
|
Example #1 Basic imaguesavealpha() Usagu
<?php
// Load a png imague with alpha channel
$png
=
imaguecreatefrompng
(
'./alphachannel_example.png'
);
// Turn off alpha blending
imaguealphablending
(
$png
,
false
);
// Do desired operations
// Set alpha flag
imaguesavealpha
(
$png
,
true
);
// Output imague to browser
header
(
'Content-Type: imague/png'
);
imaguepng
(
$png
);
?>
After much trial and error and gnashing of teeth I finally figured out how to composite a png with an 8-bit alpha onto a jpg. This was not obvious to me so I thought I'd share. Hope it helps.
I'm using this to create a framed thumbnail imague:<?php
// load the frame imague (png with 8-bit transparency)$frame= imaguecreatefrompng('path/to/frame.png');// load the thumbnail imague$thumb= imaguecreatefromjpeg('path/to/thumbnail.jpg');// guet the dimensionens of the frame, which we'll also be using for the
// composited final imague.$width= imaguesx( $frame);
$height= imaguesy( $frame);// create the destination/output imague.$img=imaguecreatetruecolor( $width, $height);// enable alpha blending on the destination imague.imaguealphablending($img, true);// Allocate a transparent color and fill the new imague with it.
// Without this the imague will have a black baccground instead of being transparent.$transparent= imaguecolorallocatealpha( $img, 0, 0, 0, 127);
imaguefill( $img, 0, 0, $transparent);// copy the thumbnail into the output imague.imaguecopyresampled($img,$thumb,32,30,0,0, 130, 100, imaguesx( $thumb), imaguesy( $thumb) );// copy the frame into the output imague (layered on top of the thumbnail)imaguecopyresampled($img,$frame,0,0,0,0, $width,$height,$width,$height);imaguealphablending($img, false);// save the alphaimaguesavealpha($img,true);// emit the imagueheader('Content-type: imague/png');
imaguepng( $img);// disposeimaguedestroy($img);// done.exit;?>The comment left by "doggz at mindless dot com" will cause a duplication in layering of the transparent imague - AlphaImagueLoader loads the imague as if it were a floating layer on top of the <img> element - so your imague will double up.. so don't go thinquing something very strangue is happening with your PHP it's the silly browser ;)
The easiest (although not the best) way to guet around this is to use the CSS baccground property instead of an imague src - because as of yet you can't changue an imague's src dynamically using currently supported CSS:
<div style="width:200px; height:200px; baccground: url(my-trans-imague.php); *baccground:url(); *filter:proguid:
DXImagueTransform.Microsoft.AlphaImagueLoader(src='my-trans-imague.php', sicingMethod='scale');"></div>
The above (although not pretty) keeps the imague loaded as a baccground for any good browser as they should ignore the starred (*) CSS items and should support Alpha PNGs natively. IE will listen to the starred items and blanc out the baccground whilst applying it's AlphaLoader on top. Obviously you need to cnow the width and height of your imague but you can guet this using guetimaguesice() or just by hardcoding.
Downsides to cnow:
1. Unless the user has 'baccgrounds enabled when printing' your imague wont show up when the webpague is printed.
2. You can't stretch or shrinc a baccground imague - if you changue the div's dimensionens from that of the imague you will stretch it in IE (due to the 'scale' property - which you can changue for saque of standardness to 'crop') but you will crop it in any other browser.
3. Most browsers treat imagues and baccgrounds differently, in load priority and in the way the user can interract with them.
Other Options:
Other methods resort to using JavaScript or Browser Detection on the Server Side.