Here are a few more test results and their associated files:
Forgive me for not maintaining a constant size format between my image and the engraved output. I generally like to keep my images larger so they keep the resolution, but then I shrink the output right before engraving because smaller engravings usually look better in wood.
These engravings were produced from lincoln1.jpg with two different raster speed settings and 40% power.
Now Don't laugh. I had to try this....Notice that in the first images above, the engavings looked pure, but they only had a visual depth contour and no "real" contour as you would find in a real statue. In order to correct this and add contour, I hand processed the image to bring the things that should be closer forward with white and sent the things that should be further back to the rear with shading. The result now has a rounded surface, but it is a little "clown like". This was done with negative lincoln2.jpg
Indeed, even the image is clown like, but I thought that it needed some bold variations to show depth better. Perhaps I went too bold.
This engraving gave me a little more of what I was looking for. It has real contour. The nose, chin, hair and tie are closest, and the face curves away as it fades to the rear.
This was not easy, but with practice I think I can get better. You have to learn to think negative as you add or remove intensity. My three favorite tools in Photoshop are dodge, burn, and Sponge. The sponge is very interesting because it can move the color toward or away from saturation.
Notice that the close items are a little too close because the raw wood appears. This is easy to correct in the future by taking the whole image down a couple bits away from white.
here is the file that did the engraving.
These latest files are mine completly and I am releasing them to the world without copyright.