Welcome to the site…
The problem is a photo has an infinite range of grays… A piece of wood has a very limited range of gray.
Sounds like you’ve tried adjust image…
I’ve had to resort to Gimp with some photos I’ve had to work with that had very dark/light areas that I wanted captured…
There is lots of experience with photo engraving here…
If you have not watched this video, it’s one of the best I’ve seen for explaining interval and I recommend it to anyone using a laser. For nothing else, it’s great with selecting a proper interval. Process is done on a fiber, but it works with any laser and any material.
These are done with a fiber, but he does excellent work… gives you a target of quality… it’s worth a peek 
Have fun, again, thanks for posting including the fairy 
