Intraocular Glare
Glare is hard to observe in everyday life, but affects our visual performance.
Glare limits the the range of light in images on our retinas.
It has minimal effect on Whites,
Small effects on Grays,
Substantial effects on Blacks.
Uniform Black scene segments become nonuniform retinal stimuli.
These highly nonuniform Blacks appear to be uniform.
Calculating the Retinal Image
A million to 1 range scene with Min-light background has a range of light on the retina of 10,000 to 1. But, a Max-light background scene has a retinal range of only 33 to 1.
The amount of glare on a retinal receptor, or camera pixel depends on:
a. The luminance histogram of all the scene’s pixels, and
b. The locations of light patterns in the array of all the scene’s luminances.
With CIE 1999 Glare Spread Function (GSF) we can calculate the scene’s pattern of light on retinas. This GSF measured the glare light from a point source at distances from 1 minute of arc to 60 degrees. The convolution of the array of all scene luminances with the GSF equals the pattern of light on the retina. [ McCann and Vonikakis, 2018 ]
Glare in Illusions
While Natural Scenes, and HDR images, have million to 1 ranges of light, printed pages in uniform illumination have only 100 to 1 ranges. Lightness Illusions contain two identical scene-luminance “Gray” segments that are identified as the “regions-of-interest” (ROI). Those segments appear identical if the “rest-of-the-scene” is restricted to a single uniform luminance. However, the designers of Illusions introduce clever “rest-of-the-scenes” that makes two identical GRAYROI luminances have different appearances in the same scene.
The fact that "the-rest-of-the-scene” changes the appearances of the GRAYROIs proves that appearances are scene-dependent. That is, the content and spatial arrangement of "the-rest-of-the-scene” transforms the quanta catch of the retinal receptors into the appearances we see.
Our visual system makes two independent scene-dependent transformations of the scene. The first is the optical GSF that degrades the image on the receptors. The second transformation is neural. It spatially enhances the array of receptor responses, counteracts glare, and generates the appearances we call Lightness Illusions.
Pseudocolor visualizes Gradients
Intraocular glare affects Lightness Illusions by spatially re-distrbutiing light from the scene's brightest segments into its darkest ones. These Illusions are LDR (range 200:1).
Illusions are made of pairs of identical Regions of Interest (ROI) segments. Designers of Lightness Illusions use clever "rest-of-the-scene" to make one ROI appear lighter, and the other ROI appear darker.
Pseudocolor makes gradients visible by segmenting bands of digital values into discriminable color segments,
Frontiers
J.J. McCann, V. Vonikakis, and A. Rizzi,
"Edges and Gradients in Lightness Illusions: Role of Optical Veiling Glare”
Front. Psychol. in press
<https://www.frontiersin.org/articles/10.3389/fpsyg.2022.958787/abstract>
Frontiers Galley Proof <2022 Scene dependent>
Download Full-Resolution Pseudocolor renditions of patterns of light on the retina
Pseudocolor LUTS (cmap and 3-3-2 RGB) FIG 4
Contrast+Assimilation1 (Grayscale) FIG 5
Contrast+Assimilation1 (cmap.LUT) FIG 6
Contrast+Assimilation2 (3-3-2 RGB.LUT) FIG 7
B&W Mondrian FIG 10
Checkershadow FIG 11
5 of 9 Examples of "Glares's Paradox FIG 12
V. Vonikakis,
"Python code bbonik /retinal-contrast-glare"
<https://github.com/bbonik/retinal-contrast-glare>
IS&T Color Imaging Conference
J.J. McCann,
"Pseudocolor Analysis of Glare’s Paradox in Illusions"
Proc. IS&T Color Imaging Conference, Scottsdale, (2022).
“Lightness Illusions” (9 examples) showed Glare’s Paradox”
More glare made Grays darker; less glare made Grays lighter
Assimilation has more glare
[more ROI glare looks lighter; less ROI glare looks darker]
Questions and Comments are welcomed
Unifrom scene segments
become gradients
on receptors
Gradients are hard to see
Contrast (top) and
Assimilation (bottom)
have only Max and Min in
"the rest of the Scene"
Scene Dependent:
Light on Retina (Scene + Glare)
Receptor responses
Neural spatial comparisons
Appearance of Lightness Illusions
Scene Independent
Silver halide films
CIE XYZ (with no-light surround)
CIE CAM (any scene)
Most cameras, Displays, HDR TV
New Work:
LDR scenes (200:1 range)
Pythpn code
Lightness Illusions
(Max & Min "Rest-of-scene"
Blacks go wild!
Calculate & Analyze Image on Retina
1 scene uses 8 different images
"Glare's Paradox" (9 scenes)
Glare assists Assimilation