Simple functions to convert jpeg image in base64 string to bitmap image

function base64_to_bmp($base64_string) {
	$bmpfile = 'filename.bmp';
	if(file_exists($bmpfile)){		
		unlink($bmpfile);
	}
	$imageSource = imagecreatefromstring(base64_decode($base64_string));
	imagebmp($imageSource,$bmpfile);
}
function imagebmp(&$im, $filename = ""){
    if (!$im) return false;
    $w = imagesx($im);
    $h = imagesy($im);
    $result = '';
    if (!imageistruecolor($im)) {
        $tmp = imagecreatetruecolor($w, $h);
        imagecopy($tmp, $im, 0, 0, 0, 0, $w, $h);
        imagedestroy($im);
        $im = & $tmp;
    }
    $biBPLine = $w * 3;
    $biStride = ($biBPLine + 3) & ~3;
    $biSizeImage = $biStride * $h;
    $bfOffBits = 54;
    $bfSize = $bfOffBits + $biSizeImage;
    $result .= substr('BM', 0, 2);
    $result .=  pack ('VvvV', $bfSize, 0, 0, $bfOffBits);
    $result .= pack ('VVVvvVVVVVV', 40, $w, $h, 1, 24, 0, $biSizeImage, 0, 0, 0, 0);
    $numpad = $biStride - $biBPLine;
    for ($y = $h - 1; $y >= 0; --$y) {
        for ($x = 0; $x < $w; ++$x) {
            $col = imagecolorat ($im, $x, $y);
            $result .=  substr(pack ('V', $col), 0, 3);
        }
        for ($i = 0; $i < $numpad; ++$i)
            $result .= pack ('C', 0);
    }
    if($filename==""){
        echo $result;
    }
    else
    {
        $file = fopen($filename, "wb");
        fwrite($file, $result);
        fclose($file);
    }
    return true;
}