PHP图片上传添加背景颜色？

Question

使用下面的PHP脚本，如果图像是透明的，我将如何添加添加#ffffff背景颜色的功能，因为我不想要黑色背景。

由于

function uploadImage($inputName, $uploadDir){       
    $image     = $_FILES[$inputName];
    $imagePath = '';

    // if a file is given
    if (trim($image['tmp_name']) != '') {
        // get the image extension
        $ext = substr(strrchr($image['name'], "."), 1); 

        // generate a random new file name to avoid name conflict
        $imagePath = md5(rand() * time()) . ".$ext";

        // check the image width. if it exceed the maximum
        // width we must resize it
        $size = getimagesize($image['tmp_name']);

        if ($size[0] > MAX_WP_LOGO_IMAGE_WIDTH) {
            $imagePath = createThumbnail($image['tmp_name'], $uploadDir . $imagePath, MAX_WP_LOGO_IMAGE_WIDTH);
        } else {
            // move the image to category image directory
            // if fail set $imagePath to empty string
            if (!move_uploaded_file($image['tmp_name'], $uploadDir . $imagePath)) {
                $imagePath = '';
            }
        }   
    }


    return $imagePath;
}

createThumbnail功能

function createThumbnail($srcFile, $destFile, $width, $quality = 75)
{
    $thumbnail = '';

    if (file_exists($srcFile)  && isset($destFile))
    {
        $size        = getimagesize($srcFile);
        $w           = number_format($width, 0, ',', '');
        $h           = number_format(($size[1] / $size[0]) * $width, 0, ',', '');

        $thumbnail =  copyImage($srcFile, $destFile, $w, $h, $quality);
    }

    // return the thumbnail file name on sucess or blank on fail
    return basename($thumbnail);
}