Renate asked how I use Photoshop to help me define areas of color (which I mentioned when I described how I made my "Midsomer Tomato" quilt above, so I thought I'd demonstrate here.
First, you start with a photo. Here's one of some hydrangea florets that I took a few summers ago.
I open it in Photoshop, and go to the "filters" menu, then under the "Artistic" filter options, choose "cut out." It selects color areas for you. One click, and voila:
When you choose the "cut out" filter, a menu will pop up that will allow you to slide bars to select edge fidelity, color complexity, and the like. You can slide them back and forth to see what they do, but they provide various ways of adding or subtracting detail. If you bear in mind that you're going to try to use the color areas you see as pieces of fabric, you'll remember that keeping it simple while including just the detail you need is the goal. Here's a simpler version of the same image:
Remember, you can add back detail with thread wok. So maybe all you want is a fabric base on which to thread paint more color and detail? Or maybe you want the fabric to do the work, so you'll want more detail? It's up to you.
Once I get to this point, I print out the image at what I want the finished size to be. (I often have to do this by taping 8 x 11 sheets together because that's all my printer will do.) Then, with a black relatively heavy-line black sharpy, I trace the color areas.
Here's a shot of the tomato one:
You can see that I take each color (in the tomato case, I had reds, blues, and greens) and I assign Dark, Light and Medium value labels.
Then I trace the whole thing onto tracing paper, and then I trace pattern shapes and assemble from there using the marked image as my guide. It's sort of tedious but it's really fun to see the picture taking shape. I don't follow this slavishly -- it's meant to be a fabric painting, after all, not a paint-by-number project. So use your artistic judgment and have fun.
I should add that I never use Photoshop Elements so I don't know if Elements as a "cutout" filter. Sometimes there is a filter called Posterize that can do similar things.