上传和调整Png大小会产生一个黑色的背景图像

我使用下面的类来裁剪，调整大小和上传图像。但当我试图上传文件时，它产生了一个黑色背景的png图像。

我尝试了很多东西，如imageAlphaBlending和imageSaveAlpha，但他们都没有解决我的问题

我使用ImageManipulator.php从这个链接https://gist.github.com/philBrown/880506

请告诉我如何解决这个问题。谢谢你

'

/**
 * @var int
 */
protected $height;
/**
 * @var resource
 */
protected $image;
/**
 * Image manipulator constructor
 * 
 * @param string $file OPTIONAL Path to image file or image data as string
 * @return void
 */
public function __construct($file = null)
{
    if (null !== $file) {
        if (is_file($file)) {
            $this->setImageFile($file);
        } else {
            $this->setImageString($file);
        }
    }
}
/**
 * Set image resource from file
 * 
 * @param string $file Path to image file
 * @return ImageManipulator for a fluent interface
 * @throws InvalidArgumentException
 */
public function setImageFile($file)
{
    if (!(is_readable($file) && is_file($file))) {
        throw new InvalidArgumentException("Image file $file is not readable");
    }
    if (is_resource($this->image)) {
        imagedestroy($this->image);
    }
    list ($this->width, $this->height, $type) = getimagesize($file);
    switch ($type) {
        case IMAGETYPE_GIF  :
            $this->image = imagecreatefromgif($file);
            break;
        case IMAGETYPE_JPEG :
            $this->image = imagecreatefromjpeg($file);
            break;
        case IMAGETYPE_PNG  :
            $this->image = imagecreatefrompng($file);
            break;
        default             :
            throw new InvalidArgumentException("Image type $type not supported");
    }
    return $this;
}
/**
 * Set image resource from string data
 * 
 * @param string $data
 * @return ImageManipulator for a fluent interface
 * @throws RuntimeException
 */
public function setImageString($data)
{
    if (is_resource($this->image)) {
        imagedestroy($this->image);
    }
    if (!$this->image = imagecreatefromstring($data)) {
        throw new RuntimeException('Cannot create image from data string');
    }
    $this->width = imagesx($this->image);
    $this->height = imagesy($this->image);
    return $this;
}
/**
 * Resamples the current image
 *
 * @param int  $width                New width
 * @param int  $height               New height
 * @param bool $constrainProportions Constrain current image proportions when resizing
 * @return ImageManipulator for a fluent interface
 * @throws RuntimeException
 */
public function resample($width, $height, $constrainProportions = true)
{
    if (!is_resource($this->image)) {
        throw new RuntimeException('No image set');
    }
    if ($constrainProportions) {
        if ($this->height >= $this->width) {
            $width  = round($height / $this->height * $this->width);
        } else {
            $height = round($width / $this->width * $this->height);
        }
    }
    $temp = imagecreatetruecolor($width, $height);
    imagecopyresampled($temp, $this->image, 0, 0, 0, 0, $width, $height, $this->width, $this->height);
    return $this->_replace($temp);
}
/**
 * Enlarge canvas
 * 
 * @param int   $width  Canvas width
 * @param int   $height Canvas height
 * @param array $rgb    RGB colour values
 * @param int   $xpos   X-Position of image in new canvas, null for centre
 * @param int   $ypos   Y-Position of image in new canvas, null for centre
 * @return ImageManipulator for a fluent interface
 * @throws RuntimeException
 */
public function enlargeCanvas($width, $height, array $rgb = array(), $xpos = null, $ypos = null)
{
    if (!is_resource($this->image)) {
        throw new RuntimeException('No image set');
    }

    $width = max($width, $this->width);
    $height = max($height, $this->height);
    $temp = imagecreatetruecolor($width, $height);
    if (count($rgb) == 3) {
        $bg = imagecolorallocate($temp, $rgb[0], $rgb[1], $rgb[2]);
        imagefill($temp, 0, 0, $bg);
    }
    if (null === $xpos) {
        $xpos = round(($width - $this->width) / 2);
    }
    if (null === $ypos) {
        $ypos = round(($height - $this->height) / 2);
    }
    imagecopy($temp, $this->image, (int) $xpos, (int) $ypos, 0, 0, $this->width, $this->height);
    return $this->_replace($temp);
}
/**
 * Crop image
 * 
 * @param int|array $x1 Top left x-coordinate of crop box or array of coordinates
 * @param int       $y1 Top left y-coordinate of crop box
 * @param int       $x2 Bottom right x-coordinate of crop box
 * @param int       $y2 Bottom right y-coordinate of crop box
 * @return ImageManipulator for a fluent interface
 * @throws RuntimeException
 */
public function crop($x1, $y1 = 0, $x2 = 0, $y2 = 0)
{
    if (!is_resource($this->image)) {
        throw new RuntimeException('No image set');
    }
    if (is_array($x1) && 4 == count($x1)) {
        list($x1, $y1, $x2, $y2) = $x1;
    }
    $x1 = max($x1, 0);
    $y1 = max($y1, 0);
    $x2 = min($x2, $this->width);
    $y2 = min($y2, $this->height);
    $width = $x2 - $x1;
    $height = $y2 - $y1;
    $temp = imagecreatetruecolor($width, $height);
    imagecopy($temp, $this->image, 0, 0, $x1, $y1, $width, $height);
    return $this->_replace($temp);
}
/**
 * Replace current image resource with a new one
 * 
 * @param resource $res New image resource
 * @return ImageManipulator for a fluent interface
 * @throws UnexpectedValueException
 */
protected function _replace($res)
{
    if (!is_resource($res)) {
        throw new UnexpectedValueException('Invalid resource');
    }
    if (is_resource($this->image)) {
        imagedestroy($this->image);
    }
    $this->image = $res;
    $this->width = imagesx($res);
    $this->height = imagesy($res);
    return $this;
}
/**
 * Save current image to file
 * 
 * @param string $fileName
 * @return void
 * @throws RuntimeException
 */
public function save($fileName, $type = IMAGETYPE_JPEG)
{
    $dir = dirname($fileName);
    if (!is_dir($dir)) {
        if (!mkdir($dir, 0755, true)) {
            throw new RuntimeException('Error creating directory ' . $dir);
        }
    }
    try {
        switch ($type) {
            case IMAGETYPE_GIF  :
                if (!imagegif($this->image, $fileName)) {
                    throw new RuntimeException;
                }
                break;
            case IMAGETYPE_PNG  :
                if (!imagepng($this->image, $fileName)) {
                    throw new RuntimeException;
                }
                break;
            case IMAGETYPE_JPEG :
            default             :
                if (!imagejpeg($this->image, $fileName, 95)) {
                    throw new RuntimeException;
                }
        }
    } catch (Exception $ex) {
        throw new RuntimeException('Error saving image file to ' . $fileName);
    }
}
/**
 * Returns the GD image resource
 *
 * @return resource
 */
public function getResource()
{
    return $this->image;
}
/**
 * Get current image resource width
 *
 * @return int
 */
public function getWidth()
{
    return $this->width;
}
/**
 * Get current image height
 *
 * @return int
 */
public function getHeight()
{
    return $this->height;
}

} '