Inversion Illusion

(Intensity and Up-Down)

We interpret two dimensional images of three dimensional objects using shading as a visual cue, assuming light to come from above.

The 'hole', might still appear to be a hole, although this 'negative' image is difficult to interpret.

The 'hole' doesn't look much like a hole any more (at least to me), although I still can see all the other little 'holes' correctly.