3 Scan in the sketch at high resolution
I return to my original detailed sketch, scan it in at 300DPI and I adjust the contrast to achieve pure white and black. I have to clean my drawing from dirt that came with the scan. Then I create an empty layer. I go to Channel and select the picture (Cmd+ Shift+ click), then use Invert (Cmd+ Shift+I). I go back to the layer and fill it with the Paint tool.