transparent background image bug

[fefescript84]

If you have a transparent background png the alpha channel will failing...bugfix:
class GDLuminanceSource ...
...
public function GDLuminanceSource($gdImage, $width, $height)
{
...
for ($j = 0; $j < $height; $j++) {
for ($i = 0; $i < $width; $i++) {
$argb = imagecolorat($this->$gdImage, $i, $j);
$pixel = imagecolorsforindex($this->$gdImage, $argb);
$r = $pixel['red'];
$g = $pixel['green'];
$b = $pixel['blue'];
$a = $pixel['alpha']; //0..127
if ( $a >= 63 ) {
$this->luminances[] = 255;
} else {
if ($r == $g && $g == $b) {
// Image is already greyscale, so pick any channel.
$this->luminances[] = $r;//(($r + 128) % 256) - 128;
} else {
// Calculate luminance cheaply, favoring green.
$this->luminances[] = ($r + 2 * $g + $b) / 4;//(((($r + 2 * $g + $b) / 4) + 128) % 256) - 128;
}
}
}
}

[fefescript84]

Please somebody test it...
class IMagickLuminanceSource
...
public function _IMagickLuminanceSource(\Imagick $image, $width, $height)
{
...
$map = 'RGBA';
$mapLen = strlen($map);
// $image->newPseudoImage(0, 0, "magick:rose");
//$pixels = $image->exportImagePixels(1, 1, $width, $height, "RGB", \Imagick::PIXEL_CHAR);
$pixels = $image->exportImagePixels(1, 1, $width, $height, $map, \Imagick::PIXEL_CHAR);

    $array = [];
    $rgb   = [];

    $countPixels = count($pixels);
    for ($i = 0; $i < $countPixels; $i += $mapLen) {
        $r = $pixels[$i] & 0xff;
        $g = $pixels[$i + 1] & 0xff;
        $b = $pixels[$i + 2] & 0xff;
        $a = $pixels[$i + 3] & 0xff; //0: transparent
        if ( $a <= 63 ) { 
            $this->luminances[] = 255;
        } else {

            if ($r == $g && $g == $b) {
// Image is already greyscale, so pick any channel.

                $this->luminances[] = $r;//(($r + 128) % 256) - 128;
            } else {
// Calculate luminance cheaply, favoring green.
                $this->luminances[] = ($r + 2 * $g + $b) / 4;//(((($r + 2 * $g + $b) / 4) + 128) % 256) - 128;
            }
        }
    }