Kees van Overveld From Light to Enlightenment – sampling -1- The sampling layer sampling – background of spatial vision and color-vision (and the perception of dynamical phenomena) isotropic and anisotropic detectors sampling and color sampling and meaning

Kees van Overveld sampling of the light field sea combat: a metafor for sampling-as-reconstruction -2- the enemy playfield (reality) … … containing the enemy fleet (things from reality) my representation of the enemy playfield (the HVS) results of my measurements (sampling) the enemy playfield (measurements in the HVS)… the (sometimes: wrong) hypotheses on the enemy fleet based on my measurements (the mental reconstruction of things in reality) From Light to Enlightenment – sampling

Kees van Overveld -3- finitely many samples to represent infinitely much information: errors (aliasing) remedy: low- pass filtering (make sure no small-scale details are present) From Light to Enlightenment – sampling sampling of the light field

Kees van Overveld what constitutes visual sampling? In the image plane (retina,...), light intensity is a function of location (x,y), time (t), and wavelength ( ) being measured with detectors, each with their own footprint, both for x,y,t, and. domain of the detector sensitivity not sensitivesensitivenot sensitive sensitivenot sensitiveinverted sensitivity -4- From Light to Enlightenment – sampling sampling of the light field

Kees van Overveld -5- … furthermore: detectors with a footprint in sombrero-shape From Light to Enlightenment – sampling sampling of the light field

Kees van Overveld -6- From Light to Enlightenment – sampling sampling of the light field

Kees van Overveld -7- Anisotropic filters are only sensitive for intensity-transitions aligned with their own orientation From Light to Enlightenment – sampling sampling of the light field

Kees van Overveld Properties of various types of detectors -8- two slightly different signals … …sampled with a single broad footprint can not be distinguished signal present no signal signal present small signal …sampled with multiple narrow footprints can be distinguished From Light to Enlightenment – sampling sampling of the light field

What is 'seen' by which detector? various footprints measure various aspects of a distribution of color or brightness: Kees van Overveld “as long as there is energy (light), it is seen” “as long as there is an oriented transition, it is seen” “as long as there is a difference from a background, it is seen” -9- From Light to Enlightenment – sampling

Kees van Overveld -10- The size of the footprint – perspective, distance and scale From Light to Enlightenment – sampling

Kees van Overveld -11- From Light to Enlightenment – sampling The size of the footprint – perspective, distance and scale

Kees van Overveld isotropic and anisotropic detectors -12- these are no 'mental images' – rather, they are outcomes of measurements in the sampling layer, imposing constraints on a (re)constructed mental image. brightness and en color distributions vertical transitions horizontal transitions borders in arbitrary direction From Light to Enlightenment – sampling

Kees van Overveld -13- visual aquity, contrast, and seeing details From Light to Enlightenment – sampling

Kees van Overveld From physical spectra to the subjective sensation of color nm 800 nm wavelength energy perwavelength intervalrelative sensitivityper wavelengthinterval sampling a spectrum with 'short wavelength' detectors sampling a spectrum with 'medium wavelength' detectors sampling a spectrum with 'long wavelength' detectors … yields a representation of any spectrum in precisely 3 'numbers' (measurements) – let's say X,Y,Z. From Light to Enlightenment – sampling

Kees van Overveld Color space: sampling spectra with three different footprints -17- So: any spectrum is interpreted as a collection of three measured values From Light to Enlightenment – sampling

Kees van Overveld Color space: mixing (altering) colors by adding or filtering -18- Mixing of light colors: spectra are perceived simulatenously. The resulting spectrum is the sum of the spectra. The measured (perceived) values are the sums of the individual measured values in each of the three channels. Hence: linear color space- behavior of subjective color. light Mixing of colored paint or by colored filters. The resulting spectrum is, for each wavelength, the product of the light spectrum and the filter 'spectrum'. Perceived values are NOT the product of the individula measured values in each of the three channels. light filter / reflector From Light to Enlightenment – sampling

Kees van Overveld -19- Color matching: assigning intersubjective coordinates to subjective color From Light to Enlightenment – sampling

Kees van Overveld Make X,Y,Z independent of intensity by normalizing: x=X/(X+Y+Z) y=Y/(X+Y+Z) z=Z/(X+Y+Z) consider a plane in x-y-z- space for z=constant: x: 0…1 y: 0…1 a straight line in XYZ maps to a straight line in xy (where did we see that before...? Perspective!) adding colors additively = adding spectra = in xy space: linear interpolation monochrome colors (rainbow colors) are on the border of a diagram; you cannot go beyond since additon coefficients cannot be <0 The red/violet line contains colors, not in the rainbow. These are mixed from two extreme rainbow colors -20- CIE-diagram From Light to Enlightenment – sampling From physical spectra to the subjective sensation of color

Kees van Overveld Color space - an intersubjective 3D representation of subjective colors -21- From Light to Enlightenment – sampling

Kees van Overveld 3D color space – alternative geometric representations -22- From Light to Enlightenment – sampling

Kees van Overveld Consequences of CIE diagram -23- Each color (such as X) can be reproduced by additive mixing of no more than two well-chosen monochrome spectra (e.g. A and B or C and D) with appropriate mixing ratios. From Light to Enlightenment – sampling

Kees van Overveld -24- Complementary colors are colors that, additively mixed together, form white or grey. After images are complementary: there are neural correlates for differences of primary colors Complementary colors give maximal hue contrast. Distance to white point: saturation. Rainbow colors hence are maximally saturated. From Light to Enlightenment – sampling Consequences of CIE diagram

Kees van Overveld Color illusions: do we actually see colors or do we estimate  ? (Retinex theory – 1970-ies) -25- From Light to Enlightenment – sampling

Kees van Overveld Georges Seurat ( ; pointillism) painting on the 'sampling layer' paradox: approximate additive color mixing with colored paint -26- From color spectra to subjective color sensation From Light to Enlightenment – sampling

Kees van Overveld -27- Meaning at the sampling layer Differences in locations: above - below From Light to Enlightenment – sampling

Kees van Overveld -28- From Light to Enlightenment – sampling Meaning at the sampling layer Differences in locations: above - below

Kees van Overveld -29- Colors and their connotation in nature and culture From Light to Enlightenment – sampling Meaning at the sampling layer