PHP 8.1.0 RC 2 available for testing

imagesavealpha

(PHP 4 >= 4.3.2, PHP 5, PHP 7, PHP 8)

imagesavealphaPNG görüntüleri kaydederken alfa kanalı bilgisinin saklanıp saklanmayacağını belirtir

Açıklama

imagesavealpha(GdImage $görüntü, bool $alfa_kaydet): bool

imagesavealpha() işlevi PNG görüntüleri kaydederken (tek renkli şeffaflığın tersine) alfa kanalı bilgisinin tamamının saklanması için seçenek belirtir.

Alfa kanal bilgisinin durduğu yerde kalması için alfa harmanlamayı devreden çıkarmalısınız (imagealphablending($im, false)).

Değiştirgeler

görüntü

imagecreatetruecolor() gibi bir görüntü oluşturma işlevinden dönen bir GdImage nesnesi.

alfa_kaydet

Alfa kanalının saklanıp saklanmayacağını belirtilir; false öntanımlıdır.

Dönen Değerler

Başarı durumunda true, başarısızlık durumunda false döner.

Sürüm Bilgisi

Sürüm: Açıklama
8.0.0 görüntü değiştirgesinde artık bir GdImage nesnesi aktarmak gerekiyor; evvelce resource türünde bir değer gerekirdi.

Örnekler

Örnek 1 - Temel imagesavealpha() kullanımı

<?php
// Alfa kanalları olan bir png gürüntüyü yükle
$png imagecreatefrompng('./alphachannel_example.png');

// Gerekli işlemleri yap

// Alfa harmanlamasını kapat
imagealphablending($pngfalse);

// Gerekli işlemleri yap

// Alfa saklama seçeneğini etkin kıl
imagesavealpha($pngtrue);

// Görüntüyü tarayıcıya gönder
header('Content-Type: image/png');

imagepng($png);
imagedestroy($png);
?>

Ayrıca Bakınız

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User Contributed Notes 2 notes

up
18
ray hatfield
10 years ago
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 image:

<?php
// load the frame image (png with 8-bit transparency)
$frame = imagecreatefrompng('path/to/frame.png');

// load the thumbnail image
$thumb = imagecreatefromjpeg('path/to/thumbnail.jpg');

// get the dimensions of the frame, which we'll also be using for the
// composited final image.
$width = imagesx( $frame );
$height = imagesy( $frame );

// create the destination/output image.
$img=imagecreatetruecolor( $width, $height );

// enable alpha blending on the destination image.
imagealphablending($img, true);

// Allocate a transparent color and fill the new image with it.
// Without this the image will have a black background instead of being transparent.
$transparent = imagecolorallocatealpha( $img, 0, 0, 0, 127 );
imagefill( $img, 0, 0, $transparent );

// copy the thumbnail into the output image.
imagecopyresampled($img,$thumb,32,30,0,0, 130, 100, imagesx( $thumb ), imagesy( $thumb ) );

// copy the frame into the output image (layered on top of the thumbnail)
imagecopyresampled($img,$frame,0,0,0,0, $width,$height,$width,$height);

imagealphablending($img, false);

// save the alpha
imagesavealpha($img,true);

// emit the image
header('Content-type: image/png');
imagepng( $img );

// dispose
imagedestroy($img);

// done.
exit;
?>
up
-2
phil at unabacus dot net
13 years ago
The comment left by "doggz at mindless dot com" will cause a duplication in layering of the transparent image - AlphaImageLoader loads the image as if it were a floating layer on top of the <img> element - so your image will double up.. so don't go thinking something very strange is happening with your PHP it's the silly browser ;)

The easiest (although not the best) way to get around this is to use the CSS background property instead of an image src - because as of yet you can't change an image's src dynamically using currently supported CSS:

<div style="width:200px; height:200px; background: url(my-trans-image.php); *background:url(); *filter:progid:
DXImageTransform.Microsoft.AlphaImageLoader(src='my-trans-image.php', sizingMethod='scale');"></div>

The above (although not pretty) keeps the image loaded as a background 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 blank out the background whilst applying it's AlphaLoader on top. Obviously you need to know the width and height of your image but you can get this using getimagesize() or just by hardcoding.

Downsides to know:

1. Unless the user has 'backgrounds enabled when printing' your image wont show up when the webpage is printed.

2. You can't stretch or shrink a background image - if you change the div's dimensions from that of the image you will stretch it in IE (due to the 'scale' property - which you can change for sake of standardness to 'crop') but you will crop it in any other browser.

3. Most browsers treat images and backgrounds differently, in load priority and in the way the user can interact with them.

Other Options:

Other methods resort to using JavaScript or Browser Detection on the Server Side.
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