I have an idea. Use the black and white picture or make your own by laying folded fabrics on the glass of your printer overlapping them and choose black to print. Print a picture of the fabrics. Then line up the fabrics from darkest to lightest and rescan. Maybe you will determine which would work for the darkest pieces and which would be for the lightest. I would try it with one block and see what you get. You could always then throw in a darker or lighter fabric to get the design you want. Please post a picture of your end result.