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Atmospheric light scattering: Difference between revisions
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* The really optically thick clouds are drawn by the weather system as separate models into the scene. | * The really optically thick clouds are drawn by the weather system as separate models into the scene. | ||
== Perception == | |||
One crucial thing to remember when dealing with light attenuation is that what we see is <b>not</b> physical light intensity. To give an example, the light intensity beneath an overcast sky at dawn is easily a factor 2500 less than the light intensity in the bright noon sun. However, dividing an rgb vector of (1,1,1) (white light) by 2500 and using the result for lighting the overcast dawn results in a pitch black scene. The reason is that the eye adapts to different light intensities and that in essence perception weighs intensities over a wide range not linear but logarithmically, a phenomenon known as the [http://en.wikipedia.org/wiki/Weber-Fechner_Law Weber-Fechner law]. | |||
Another perception effect is that contrasts are dynamically adjusted. Usually the brightest object in the visual field is assigned the color white, the darkest the color black, and all other shades are assigned between. This means that the raw intensity range in the scene has to be compressed (e.g. by exposure filtering) into a narrower range by dimming the highest intensities and enhancing the lowest intensities. | |||
Perception effects require thus some amount of postprocessing in the shaders. | |||