Programatically extract pattern from image file and / or PSD

I often have to extract a pattern from a PSD to make an image to be used with XHTML and CSS.

I have often just made a guess in Photoshop, and then had to correct my guesses a few time after. It seems cumbersome.

Is there...

• Techniques for extracting a pattern from a Photoshop file with the selector tool?
• A Photoshop plugin perhaps that can do this
• Software that can parse a pattern image, and give me back the bare minimum to make a tiled pattern?

Should I just be requesting a copy of the pattern in addition to each PSD I receieve?

How have other people in my position tackled this problem before?

In matter of interest, how could / would I program something like this (I could use PHP with GD library)? Is it not worth my time? Would I loop through pixels left to right, and then identify image colours, and positions away from each other, and constantly check if new pixels are beginning to match开发者_如何学C an older pattern?

I'm currently working on a software that does this (and a couple more things to automate slicing of PSDs), but it's very slow even in C++. Right now i'm looking into GPU accelerated solution... So if there's an option for requesting pattern you should just do that.