Photoshop :: Create A Pattern From Source Images?

I am currently using Photoshop CS4.Anyway, I want to make a grid, not necessarily with square grid blocks, then attach an image to a new layer underneath the grid. Then I want something that will go grid block by grid block, look for the predominant color of the attachment image within that grid block, and fill that entire grid block with that color. The images I am looking to attach are cartoon style (i.e. logos), and there are not complex color schemes to work with. The Pixelize effect is similar, except that it gives a blend of the colors which may not be in the grid space to begin with. i.e., if only black and white is used in an image, it might spit out a gray color shade rather than black or white. I am essentially trying to create a pattern from source images.