Some time ago, I believe Al asked about a height pattern showing gray scale for a pattern. I have made up such a pattern, for you to download and look at. Plus I have included 2 images in PNG format. One without text for importing if you like, so you can use it in PE. The other with text showing the tool height if this shade of gray was used. I need to explain tool height so everyone understands what I am talking about. Tool height is the height of the tool from the base of your carving. Lets say your carve is .25" deep. Then using the shade of gray for .01" will give you a depth of .25-.01=.24" from the top of the board. If you use .5" deep, then you will get a depth for that same shade of gray of .49" deep. Tool height is from the bottom of your carve region.
With that said enjoy the pattern place it on a board run your cursor over each section and you will see the depth mentioned above. Use this to create your heights in a photo editing program knowing you will get the exact height you want for each area you shade with gray.