Php 在GD IMG_FILTER_着色后将背景应用于PNG透明图像

我有一个透明的png图像（它是单色的），我应用了彩色php GD过滤器。所以现在它是彩色的，但我很难用白色背景来消除透明度

    list($r,$g,$b) = array_map('hexdec',str_split($ColourPrimary,2));
    $r = $r - 52;
    $g = $g - 52;
    $b = $b - 52;

    imagesavealpha($im, true);
    imagefilter($im, IMG_FILTER_COLORIZE, $r, $g, $b);

    $bw  = imagesx($im);
    $bh = imagesy($im);
    $background = imagecreatetruecolor($bw,$bh);
    $bkwhite = imagecolorallocate($background, 255, 255, 255);
    imagefill($background,0,0,$bkwhite);
    imagecopy($background, $im, 0, 0, 0, 0, $bw, $bh);

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睡了一个好觉后，我意识到我是在倒退。我首先应用了背景，然后在顶部复制了图像

    list($r,$g,$b) = array_map('hexdec',str_split($ColourPrimary,2));
    $r = $r - 52;
    $g = $g - 52;
    $b = $b - 52;

    $imfore = imagecreatefrompng(FILELOCATION);
    imagesavealpha($imfore, true);
    imagefilter($imfore, IMG_FILTER_COLORIZE, $r, $g, $b);
    $bw  = imagesx($imfore);
    $bh = imagesy($imfore);

    $im = imagecreatetruecolor($bw,$bh);
    $bkwhite = imagecolorallocate($im, 255, 255, 255);
    imagefill($im,0,0,$bkwhite);
    imagecopy($im, $imfore, 0, 0, 0, 0,$bw,$bh);