Graphic Manipulation help!

[mosaicmedia]

I am building an application that creates a label for a manufacturing company... it finds an appropriate font size for given text, and then draws it and displays the image as a bmp(it is required to be a bmp).  That is all fine and dandy and working correctly.  The problem is that the label must have a depth of 2 bits for it to work correctly on their machine...I am using the following code, but cannot get a bit depth lower than 24.  iMagick and GD are both available on the server.

 

$text = $_GET['text'];

if (isset($text)) {



	$image = new Imagick();
	$image->setResolution(71.5, 71.5);
	$image->newImage(160, 40, new ImagickPixel('black'));

	$draw = new ImagickDraw();
	$draw->setFillColor('white');
	$draw->setStrokeColor(new ImagickPixel('black'));
	$draw->rectangle(0, 0, 159, 39);

	$font_size = 25;
	$font_name = 'arial.ttf';

	do
	{
		$font_size--;
		$bbox=imagettfbbox($font_size, 0, $font_name, stripcslashes($text));
		$right_text = $bbox[2];
		$left_text = $bbox[0];
		$width_text = $right_text - $left_text;
		$height_text = abs($bbox[7] - $bbox[1]);
	}
	while ($font_size>9 && ($height_text>40 || $width_text>160));

	if ($height_text>40 || $width_text>160 || $font_size<10)
	{
		echo 'The text given will not fit on the label.<br />';
	}
	else
	{
		$draw->setFont($font_name);
		$draw->setFontSize($font_size);
		$draw->setFillColor('black');
		$draw->setTextAntialias(false);
		$draw->setGravity (Imagick::GRAVITY_CENTER);
		$draw->annotation(0, 0, stripcslashes($text));

		$image->drawImage($draw);
		$image->blackthresholdImage( "#999999" );
		$image->whitethresholdImage( "#999999" );

		$image->setImageType(1);

		$image->setImageFormat('bmp');

		$image->writeImage("flavor_labels/".$text.".bmp");
		echo '<img src="flavor_labels/'.$text.'.bmp" /><br /><p>Right click this image and click Save As or Save Image As.  <br />Enter in the desired label name and save it to the desired destination.</p>';

	}

}