You can use this test pattern to determine the correct thickness of material you need for different brightness values.
If you don't want to print a 100x100 test part, then scale the XY, but do not scale the Z.
If your material needs to be thicker than 3mm to be fully dark, then just scale the test model in the Z axis by 2X, and multiply the resulting values accordingly.
If you are looking for a Lithophane conversion tool:
http://3dp.rocks/lithophane/
Good Luck!!!
NOTE!!!
Under no circumstance should you use pre-generated .gcode files, it is extremely risky and could damage your printer. Always slice the files yourself.
Rafts: No
Supports: No
Resolution: 100 micron
Infill: 100%
The author marked this model as their own original creation. Imported from Thingiverse.