Originally Posted by
rnclark
Another factor not discussed in this thread so for is that of visual perception, which is quite complex. For example, in bright office light, small details around 1-arc-minute in apparent size need on the order of 20% contrast to be just discernible wheres at about 20 arc-minutes in apparent size one can detect around 0.5% contrast details. The contrast detection drops (you need higher contrast) as light levels drop. So if you want to show detail in the highlights, you need to stretch the contrast for the target illumination. Reference: Blackwell, R.H., Contrast Thresholds of the Human Eye, Journal of the Optical Society of America, v36, p624-643, 1946. Roger