RGB “Time Snapshots” and Land’s Retinex’s

by Gerald Huth on July 14, 2005

Vision literature generally treats longitudinal chromatic aberration (LCA) as an “aberration” describing the “blur circle” that it creates around the visual image. This means that they are treating the retina as the image plane of the eye that I demonstrate is not the case! The retina is the focal or Fourier plane of the eye.

Following from yesterday’s thought that image information arrives at the retina/Fourier plane coherently (i.e., in “zero” time), the effect of LCA in the eye is to create a “focal region” that we can define as extending from the edges and exact geometric middle of the visible band. The eye focuses the longest wavelength (red) end of the band on the retina at the all-cone central fovea. The region then exends from this point into the eye. I do not know the magnitudes here but let’s say that these points focus at one millimeter increments in front of the fovea. This would correspond to a time duration of ~ 30 picoseconds ( or 10^ -12 seconds). I would note that the function of the retina then is to “extract” intensity information from these three points. Taking into account that information is brought to these points in “zero” time, the three primary color images can for the first time to my knowledge be considered differentiable,, i.e., actually can be treated as separate entities for subsequent processing of intensity information on the retina. . They then represent “snapshots” in the primary colors: red, green and blue! Let me recount here precise definitions for these regions: 1.) the RED sensitive fovea to about 1-3 degrees of retinal angle (this region may have an additional function of defining an “outline sketch” of the image – more below) 2.) retinal angles from 1-3 degrees to the GREEN mid-band defining angle at 7 1/2 degrees, and, finally, 3.) angles from 7 1/2 to ~ 20 degrees defining BLUE sensitivity. “Time snapshots” would be obtained from instantaneous interactions in these three regions.

Time Snapshots

There would seem to be an inescapable correlation of these separate “snapshot”s with Land’s separate “Retinex’s”. The “lightness records” proposed by Land I would conclude correspond to interactions in the regions on either side of the 7 1/2 degree fixed wavelength reference. I have shown that these regions respond to lightness – or intensity – with wavelength being pre-defined by refraction within the eye. Land sometimes speaks of a fourth Retinex that I conclude alludes to the separate sketch-defining function at the red wavelength. I will write more about this shortly.

And I would not believe that one must involve the brain as Land did (Retinex = retina + cortex) in color formation. I would guess that all of the necessary processing of these images (i.e., comparison of the two lightness records) is accomplished in the sub-retinal circuitry of the eye… the answer to which this new concept might give clue. There are undoubtedly “color receiving centers” in the brain (I believe demonstrated) but I would consider that they probably have a “receiving” function with color being determined within the eye. But…?


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