Imagick - get a thumbnail for each page of a PDF file

Question

I'm trying to get some information from pdf-files that i uploaded via move_uploaded_file().

I need thumbnails of each page to do some color analysis. further i need the width and height of each page in an actual unit of distance (not pixel).

is there a way to do the conversion from pdf to image in imagick not imagemagick. just because I'm using the imagick instace for the color analysis.

now this works for a single image file but not for a multipage pdf. what to do know...?

/* Read the image */
$im = new Imagick($file);

/* Thumbnail the image */
$im->thumbnailImage(null, 200);

/* Overwrite it */
file_put_contents($file, $im);

/* Gather Info */
$width = $im->getImageWidth();
$height = $im->getImageHeight();
$ratio = $width / $height;


/* Calculate gray */

$pixel_count = 0;
$sum_gray = 0;

for ($row=0;$row<$height;$row++) {
    for ($col=0;$col<$width;$col++) {
        $pixel = $im->getImagePixelColor($col, $row);
        $rgb = $pixel->getColor();
        $this_gray = .299*$rgb['r'] + .587*$rgb['g'] + .114*$rgb['b'];
        $sum_gray += $this_gray;
        $pixel_count++;
    }
} 

$gray = (1-($sum_gray / $pixel_count) / 256)*100;

and if anybody knows how to get the height and width information, plaes let me know.

thanks for the help!