GD：将PNG的白色背景设为透明

Question

我有一个透明背景的PNG水印图像。 但是随机会产生白色背景，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);

解决方法是添加：

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

完整的代码：

// 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

尝试使用imagecopymerge而不是imagecopy

编辑：尝试此代码：

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

我遇到了同样的问题，但为了使其正常工作，我从代码中注释了这两行：

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

所以我的代码看起来像这样：

$image_1 = imagecreatefrompng("example26_".$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);

现在，两张图片合并并保留了透明度，并使用这两行生成了随机的白色背景，希望这对其他遇到相同问题的人有所帮助