Final answer:
The phenomenon where image intensity is greater at the center than at the periphery is called vignetting, an effect often seen in photography.
Step-by-step explanation:
The phenomena of image intensity being greater at the center of the image than at its periphery is called vignetting. This effect is commonly seen in photography and optics when the brightness or saturation of the image decreases toward the outer edges of the photograph. It can be caused by several factors such as the design of the lens, the use of a strong light source, or a physical obstruction like a lens hood that is too small or improperly attached.
Other terms mentioned like 'quantum mottle' and 'pincushion effect' refer to different concepts. Quantum mottle is related to the statistical nature of photons in an image, and it occurs when the number of photons reaching the detector is low. The pincushion effect is a type of lens distortion where the image appears pinched at its center, an effect opposite to that of barrel distortion.