Camera sensors can capture a certain maximum number of photons before they start to saturate and no longer register additional light. Although it is impossible to increase the saturation point by increasing the capacity of the sensor electron, producing large sensors is excessively expensive and reduces sensor resolution. Such sensors are also hard to justify for general imaging applications because on average, only a small portion of a scene contains very bright spots and thus needs high capacity sensors.
The human visual system has developed a clever mechanism to cope with highly saturated scene regions, such as highlights or light sources. Like camera sensors, the photoreceptors in the human retina are also prone to saturate. However, the visual system is able to infer higher brightness of those saturated regions from glare, which is produced by the light that is scattered in the ocular fluid and spread over the retina. The glare surrounding bright areas boosts their perceived brightness, giving additional information to the brain that this part of the scene is much more than the photoreceptor saturation point. (See fig 1, Chap 1, pg 289. ‘Glare Encoding of High Dynamic Image Ranges.’)
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