A way to hide ghosting when doing partial refresh

[Ray4san]

I found that during the partial refresh process, new white pixels will affect the surrounding original black pixels. As a result, black pixels that do not need to be updated would accidently turn gray (I think you can use this way to display 4-grayscale pics).
So, when I want a partial refresh, I first fill the whole screen with black pixels and refresh with display.display(1);, then draw the next pic and do the partial refresh. With all black pixels turned gray in advance, ghosting won't appear anymore.
Actually, there still exist a little ghosting, but it does being much better especially on pics that contain a lot of scattered points. The screen only need to flash once at the first time, all the subsequent drawing that need to use partial refresh will perform better.
Hope this could help you make more creative watchfaces.