如何在PHP中以透明方式调整png的大小？

Question

我正在尝试使用PHP中的透明背景调整png的大小，而我在网上发现的代码示例对我不起作用。这是我使用的代码，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 “不起作用”是指我调整png大小时背景颜色变为黑色。

Answer 1

旧线程，但以防万一-如果正确命名，Dycey的示例应该可以工作。这是我的图像大小调整类中使用的修改版本。注意检查以确保定义了imagecolorallocatealpha（），如果使用的是GD <2.0.8，则不会。&nbsp; /**&nbsp; &nbsp; &nbsp;* usually when people use PNGs, it's because they need alpha channel&nbsp;&nbsp; &nbsp; &nbsp;* support (that means transparency kids). So here we jump through some&nbsp;&nbsp; &nbsp; &nbsp;* hoops to create a big transparent rectangle which the resampled image&nbsp;&nbsp; &nbsp; &nbsp;* will be copied on top of. This will prevent GD from using its default&nbsp;&nbsp; &nbsp; &nbsp;* background, which is black, and almost never correct. Why GD doesn't do&nbsp;&nbsp; &nbsp; &nbsp;* this automatically, is a good question.&nbsp; &nbsp; &nbsp;*&nbsp; &nbsp; &nbsp;* @param $w int width of target image&nbsp; &nbsp; &nbsp;* @param $h int height of target image&nbsp; &nbsp; &nbsp;* @return void&nbsp; &nbsp; &nbsp;* @private&nbsp; &nbsp; &nbsp;*/&nbsp; &nbsp; function _preallocate_transparency($w, $h) {&nbsp; &nbsp; &nbsp; &nbsp; if (!empty($this->filetype) && !empty($this->new_img) && $this->filetype == 'image/png')) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (function_exists('imagecolorallocatealpha')) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; imagealphablending($this->new_img, false);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; imagesavealpha($this->new_img, true);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; $transparent = imagecolorallocatealpha($this->new_img, 255, 255, 255, 127);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; imagefilledrectangle($this->new_img, 0, 0, $tw, $th, $transparent);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }