We determined the best preview to use is to view the original color image in grayscale. Picengrave calculates the depths of cut by 8bit (256) shades and that is the purpose of the "View Gray Scale" selection in the image editor and the main program. Black is the deepest cut and white is the shallowest, unless your engraving a Lithophane, then it's reversed.
Previewing a raster gcode file with short incremental & stepover toolpath moves, really does not show much. It looks like this, so it's best just to judge the outcome from the grayscale preview of your image.
Our programs generate gcode by the standard formats that grbl and other CNC controllers require for compatibility. Easel will not run the standard range of G & M code format for grbl compatibility, so it's best to use another gcode streamer that will.