New Post: Converting only a certain portion of PDF to image.

I've been trying to figure this out and can't seem to determine the proper method. I am creating an image from PDF and only need to use a certain area of it. For now, I'm resorting to cropping using a MagickGeometry. It works great, but the problem is that there's a lot of processing time and memory being wasted on the original size. Is there a way for me to only convert a certain portion of the pdf?

Any help would be greatly appreciated. Target machines have low memory and low processing power.