From Light to Enlightenment – sampling

1. From Light toEnlightenment – sampling 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 -1-

2. From Light toEnlightenment – sampling sampling of the light field sea combat: a metafor for sampling-as-reconstruction 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) Kees van Overveld -2-

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

4. sensitivity not sensitive sensitive not sensitive not sensitive sensitive inverted sensitivity not sensitive domain of the detector From Light toEnlightenment – sampling sampling of the light field 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  . Kees van Overveld -4-

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

6. From Light toEnlightenment – sampling sampling of the light field Kees van Overveld -6-

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

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

9. “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” From Light toEnlightenment – sampling What is 'seen' by which detector? various footprints measure various aspects of a distribution of color or brightness: Kees van Overveld -9-

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

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

12. From Light toEnlightenment – sampling isotropic and anisotropic detectors brightnessand en colordistributions these are no 'mental images' – rather, they are outcomes of measurements in the sampling layer, imposing constraints on a (re)constructed mental image. verticaltransitions horizontaltransitions borders in arbitrarydirection Kees van Overveld -12-

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

14. sampling a spectrum with 'short wavelength' detectors sampling a spectrum with 'medium wavelength' detectors sampling a spectrum with 'long wavelength' detectors relative sensitivity per wavelength interval energy per wavelength interval 400 nm 800 nm wavelength  From Light toEnlightenment – sampling From physical spectra to the subjective sensation of color … yields a representation of any spectrum in precisely 3 'numbers' (measurements) – let's say X,Y,Z. Kees van Overveld -14-

15. http://www.artelista.com/en/artwork/2566943631689989-colourful-fruit-composition-ii.htmlhttp://www.artelista.com/en/artwork/2566943631689989-colourful-fruit-composition-ii.html

16. http://www.artelista.com/en/artwork/2566943631689989-colourful-fruit-composition-ii.htmlhttp://www.artelista.com/en/artwork/2566943631689989-colourful-fruit-composition-ii.html

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

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 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 light light From Light toEnlightenment – sampling Color space: mixing (altering) colors by adding or filtering Kees van Overveld -18-

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

20. y: 0…1 x: 0…1 From Light toEnlightenment – sampling From physical spectra to the subjective sensation of color 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: CIE-diagram • 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 Kees van Overveld -20-

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

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

23. From Light toEnlightenment – sampling Consequences of CIE diagram 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. Kees van Overveld -23-

24. From Light toEnlightenment – sampling Consequences of CIE diagram 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. Kees van Overveld -24-

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

26. From Light toEnlightenment – sampling From color spectra to subjective color sensation Georges Seurat (1859-1891; pointillism) • painting on the 'sampling layer' • paradox: approximate additive color mixing with colored paint Kees van Overveld -26-

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

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

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