The valuation of the apparent density of a filter on a bicolored background.

When the transmittance of a filter on a bicolored background is varied, the lightness differences that vary are those between the filter and the background and that between the parts inside the filter. It is hypothesized that these are the differences of importance for the valuation of the apparent density of the transparent layer. The results of two experiments seem to show that the rated apparent density does not depend only on the lightness difference inside the filter, or only on the two lightness differences between the filter and the background. All three lightness differences would enter the valuation mechanism. An averaging model is proposed.