The Penetration of Light into Paper and Its Effect on Halftone Reproduction.

In explaining how the tones of a halftone reproduction are related to dot area, the effect of the penetration of light into the paper is usually neglected. Measurements show that the light does not emerge from the paper at exactly the spot where it entered, so that some of the light which enters through a dot emerges through white paper. It is shown that this appreciably increases the density of the middletones, especially on uncoated papers, and multiple internal reflections from the paper surface increase it still further, so that the usual simple equation relating dot area to density is not accurate.