GD：將PNG的白色背景設為透明

Question

我有一個透明背景的PNG水印圖像。 但是隨機會產生白色背景，而不是保持透明。

// Watermark
$watermark = imagecreatefrompng($docRoot . '/images/misc/watermark.png');
list($mwidth, $mheight) = getimagesize($docRoot . '/images/misc/watermark.png');

// Combinde watermark image with image already generated in $dst
imagecopy($dst, $watermark, $tnWidth-$mwidth-5, $tnHeight-$mheight-5, 0, 0, $mwidth, $mheight);

解決方法是添加：

imagealphablending($dst, true);
imagesavealpha($dst, true);

完整的代碼：

// Watermark
$watermark = imagecreatefrompng($docRoot . '/images/misc/watermark.png');
list($mwidth, $mheight) = getimagesize($docRoot . '/images/misc/watermark.png');

imagealphablending($dst, true);
imagesavealpha($dst, true);

// Combinde watermark image with image already generated in $dst
imagecopy($dst, $watermark, $tnWidth-$mwidth-5, $tnHeight-$mheight-5, 0, 0, $mwidth,

Answer 1

嘗試使用imagecopymerge而不是imagecopy

編輯：嘗試此代碼：

header('Content-type: image/jpeg');
$dst = imagecreatefromjpeg($image_path);
$watermark = imagecreatefrompng($docRoot . '/images/misc/watermark.png');
list($mwidth, $mheight) = getimagesize($docRoot . '/images/misc/watermark.png');
imagecopymerge($dst, $watermark, $tnWidth-$mwidth-5, $tnHeight-$mheight-5, 0, 0, $mwidth, $mheight, 100);
imagejpeg($dst,'',90);
imagedestroy($dst);

Answer 2

使用alpha通道保存$dst ，而不是$watermark 。

// Watermark
$watermark = imagecreatefrompng($docRoot . '/images/misc/watermark.png');
list($mwidth, $mheight) = getimagesize($docRoot . '/images/misc/watermark.png');

imagealphablending($dst, false);
imagesavealpha($dst, true);

// Combinde watermark image with image already generated in $dst
imagecopy($dst, $watermark, $tnWidth-$mwidth-5, $tnHeight-$mheight-5, 0, 0, $mwidth, $mheight);

Answer 3

我遇到了同樣的問題，但為了使其正常工作，我從代碼中注釋了這兩行：

imagesavealpha($image_1, true);
imagesavealpha($image_2, true);

所以我的代碼看起來像這樣：

$image_1 = imagecreatefrompng("example26_".$acct.".png");
$image_2 = imagecreatefrompng('example27.png');
imagealphablending($image_1, true);
imagealphablending($image_2, true);
//imagesavealpha($image_1, true);
//imagesavealpha($image_2, true);
imagecopy($image_1, $image_2, 0, 0, 0, 0, 1350, 250);
header("Content-Type: image/png");
imagepng($image_1);

現在，兩張圖片合並並保留了透明度，並使用這兩行生成了隨機的白色背景，希望這對其他遇到相同問題的人有所幫助