Optical dot gain is defined as the quantity of light, which is absorbed by a specific dot in addition to the physical dot size. This enlargement is due to the partial absorption of scattered light. By absorbing scattered light the dots seem to be larger than their original size.
When looked at via microscope the physical dot size complies directly with the bitmap hue percentage plus physical dot gain. When viewed with the naked eye (e.g. at densitometer measurement) light quantity seems to correspond exactly to a dot percentage being larger than the actual physical dot. The total optically absorptive effect of the dot normally indicates the actual dot percentage.