PHP - 如何将图像复制为透明png

Question

首先，我不是 PHP 大师。我正在使用调整图像大小和裁剪图像的功能。在我上传透明 png 之前，它运行良好。 :)

它保存黑色背景的png。我在 stackoverflow 上找到了一些答案，但我无法将它与我的代码结合起来。

这是我的功能：

//resize and crop image
function resize_crop_image($max_width, $max_height, $source_file, $dst_dir, $quality = 90){
    $imgsize = getimagesize($source_file);
    $width = $imgsize[0];
    $height = $imgsize[1];
    $mime = $imgsize['mime'];

    switch($mime){
        case 'image/gif':
            $image_create = "imagecreatefromgif";
            $image = "imagegif";
            $format = "gif";
            break;

        case 'image/png':
            $image_create = "imagecreatefrompng";
            $image = "imagepng";
            $quality = 7;
            $format = "png";
            break;

        case 'image/jpeg':
            $image_create = "imagecreatefromjpeg";
            $image = "imagejpeg";
            $format = "jpg";
            break;

        default:
            return false;
            break;
    }

    $dst_img = imagecreatetruecolor($max_width, $max_height);
    $src_img = $image_create($source_file);

    $width_new = $height * $max_width / $max_height;
    $height_new = $width * $max_height / $max_width;
    //if the new width is greater than the actual width of the image, then the height is too large and the rest cut off, or vice versa
    if($width_new > $width){
        //cut point by height
        $h_point = (($height - $height_new) / 2);
        //copy image
        imagecopyresampled($dst_img, $src_img, 0, 0, 0, $h_point, $max_width, $max_height, $width, $height_new);
    }else{
        //cut point by width
        $w_point = (($width - $width_new) / 2);
        imagecopyresampled($dst_img, $src_img, 0, 0, $w_point, 0, $max_width, $max_height, $width_new, $height);
    }


    // you can ignore these 4 lines. I'm using it for change the name.
    $nameforimage   = rand('11111111', '9999999999');
    $nameforimage2  = rand('11111111', '9999999999');
    $newname        = $nameforimage."_".$nameforimage2;
    $newdir         = $dst_dir."".$newname.".".$format;

    $image($dst_img, $newdir, $quality);

    if($dst_img)imagedestroy($dst_img);
    if($src_img)imagedestroy($src_img);

    return $newname.".".$format;

}

编辑： 好的，我找到了解决方案。

只需添加以下几行：

imagealphablending($dst_img, false);
imagesavealpha($dst_img, true);
$transparent = imagecolorallocatealpha($dst_img, 255, 255, 255, 127);
imagefilledrectangle($dst_img, 0, 0, $max_width, $max_height, $transparent);

在这一行之后：

$dst_img = imagecreatetruecolor($max_width, $max_height);

Answer 1

您必须启用保存 Alpha 通道。

可以用imagesavealpha()完成，例如：

// As per the manual, alpha blending must be disabled
imagealphablending($dst_img, false);
imagesavealpha($dst_img, true);