The overlay on the above H-a image was purposely defocused (using a mild Gaussian Blur) and the dynamic range was compressed (resulting in fewer discrete levels) to simulate what at lower resolution appears to be an almost crater-like depression in the solar chromosphere.
Moving the cursor onto the image reveals the actual topographical features as detected with higher resolution and wider dynamic range. It actually does contain a "floor" area of plage with activity rising all around and over it, but not at the exaggerated depth as perceived with lowered resolution and dynamic range. There, the darker areas lacking structure and detail, blend and create the illusion of deep shadows... an effect further enhanced by encircling filaments that seem to define an outer edge or rim... but this is merely an astro-Trompe l'oeil (fool the eye)!
Granted, dimensional variations do occur, as the chromosphere abounds in raging activity thrust from below... but optical limitations and nuances can create illusions of something that is not there (not unlike canals or faces on Mars!)
The full disk image from which these croppings were taken may be seen on my 21-July-2004 H-a page.
Depth Illusion Effects of optical limitations: things may not always be what they seem!