Rod contribution to large‐field color matching

Abstract

The linear algebraic features of foveal colorimetry do not apply to 10° degree colorimetric fields. A light presented as a foveal 2° field stimulates the three classes of cone photoreceptors, and a light presented as a 10° field stimulates the cone and rod photoreceptors. While no more than three primary lights are required to match either of these lights, large‐field color matches with three primaries do not obey Grassmann's laws of linearity because the relative contribution of the rod signal to a color match changes with retinal illuminance. A three‐primary set of color‐matching functions (CMFs) affected by rodintrusion, therefore, cannot serve as the basis for colorimetry. Stiles and Burch removed the effects of rod activity from their 10° color‐matching data to create a set of CMFs that have the same linear algebraic features as foveal, 2° colorimetry. They did this by selecting the primaries appropriately, making the matches at high retinal illuminance levels, and removing the small residual effects with numerical techniques. the resulting CMFs formed the major portion of the CIE 1964 10° Standard Observer. These CMFs describe color matches at the level of the cone‐photoreceptor and, therefore, can be generalized to predict color matches with any set of primaries, but they cannot account for the effects of rod activity in the matching sample. If two colorimetric fields differ in the amount of rod activity they produce, calculations with the 1964 Standard Observer may predict their metamerism inaccurately. This article summarizes Stiles and Burch's methods for removing the effect of rods, gives examples of the implications for colorimetry, and suggests procedures for preventing the adverse effects of rod activity in applied situations. It also shows that three recently published sets of 10° CMFs may be influenced by the effects of rod activity. © 1994 John Wiley & Sons. Inc.

Vision under mesopic and scotopic illumination

“…When both rods and cones are operational, rods influence all aspects of color vision ( Lythgoe, 1931 ; Gilbert, 1950 ; Trezona, 1970 ; Stabell and Stabell, 1975a , b, 1976 , 1979 , 1994 ; Smith and Pokorny, 1977 ; Montag and Boynton, 1987 ; Buck, 1997 ; Cao et al, 2005 ). In trichromatic observers, large field and peripherally viewed lights stimulate four different photoreceptor classes at mesopic light levels and as light level decreases, large field color matches made with three primaries do not obey Grassman’s laws ( Shapiro et al, 1994 ). Conversely, the dichromatic retina behaves similarly to the trichromatic retina with large or peripherally viewed mesopic stimuli when rods operate as the third photoreceptor class ( Smith and Pokorny, 1977 ).…”

Impact of Color Matching Primaries on Observer Matching: Part II – Observer Variability

“…Thornton (Thornton 1997) found that the inter-observer differences appeared to be large for anti-prime color (AP: 497-579-653 nm) monochromatic matching primaries, but small for prime color (PC: 452-533-607 nm) spectral composition. Since the average age of Thornton's six observers was 56 years and the average age of the CIE observer was 32 years, lens yellowing could be a factor explaining some of the discrepancies between the average data of the two groups (Shapiro et al 1994). In a re-analysis of Thornton's data, Abraham (Ábrahám et al 1995) did indeed find that there was a difference between the mean chromaticity of matches made by old and young observers when using the AP primaries, causing increased overall variability.…”

Comment 1 on ‘Lamp colour properties and apparent brightness: a review’ by SA Fotios

“…There is a large body of psychophysical literature documenting the validity of this condition, some of which is listed here. [1][2][3][4][5][6][7][8][9] In addition, objective measures of visual response using infrared technology have demonstrated that primarily the scotopic spectrum, and thus rods, controls pupil size at typical interior light levels. 10,11 Lighting practice has largely ignored all this information and thus often appears bewildered when a pure cone response (the V(l) calibrating function based on observers viewing a 2°visual field) does not agree with many brightness experiences in real lit environments.…”