如何在PHP中透明地调整png的大小？

我试图在PHP中调整透明背景的png,我在网上找到的代码示例对我不起作用.这是我正在使用的代码,建议将不胜感激!

$this->image = imagecreatefrompng($filename);

imagesavealpha($this->image, true);
$newImage = imagecreatetruecolor($width, $height);

// Make a new transparent image and turn off alpha blending to keep the alpha channel
$background = imagecolorallocatealpha($newImage, 255, 255, 255, 127);
imagecolortransparent($newImage, $background);
imagealphablending($newImage, false);
imagesavealpha($newImage, true);

imagecopyresampled($newImage, $this->image, 0, 0, 0, 0, $width, $height,  $this->getWidth(), $this->getHeight());
$this->image = $newImage;  
imagepng($this->image,$filename);

更新 "不工作"我的意思是当我调整pngs时,背景颜色会变为黑色.

据我所知,您需要在执行imagecolorallocatealpha()之前将混合模式设置为false,并将保存alpha通道标志设置为true

更新:此代码仅适用于透明度不透明度= 0的背景.如果您的图像具有0 <不透明度<100,则它将是黑色背景.

这是一个适合我的最终解决方案.

function resizePng($im, $dst_width, $dst_height) {
    $width = imagesx($im);
    $height = imagesy($im);

    $newImg = imagecreatetruecolor($dst_width, $dst_height);

    imagealphablending($newImg, false);
    imagesavealpha($newImg, true);
    $transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127);
    imagefilledrectangle($newImg, 0, 0, $width, $height, $transparent);
    imagecopyresampled($newImg, $im, 0, 0, 0, 0, $dst_width, $dst_height, $width, $height);

    return $newImg;
}