PHYS 545 R. J. Wilkes

Transcription

1 PHYS 545 R. J. Wilkes Session 8: Color, vision, perception Color blindness Optical illusions Colorimetry 1/30/18

2 See : Tonight NO FINAL EXAM - course is over after March 8 Grades will be posted on Catalyst Gradebook on or before March 19. Papers may be picked up from my office after grades are posted. 2

3 Announcements This week: Problem set 1 solutions + set 2 are posted Today s session: lecture + demonstrations Color blindness Optical illusions Land color theory demonstration Colorimetry Thursday session: Begin wave optics Take-home exam will be posted Your independent study project proposal is due Topic chosen Resources to be used Choice of deliverable: 5 p paper, or website, or in-class presentation» Number of presentations limited to 8 by time available 3

4 Announcements Next term: PCE will have online registration for classes available Only for students in MS degree program GNMs register as before You should receive info from PCE on how to register Look for a link in your MyUW page 4

5 UW CONTINUUM COLLEGE/PROFESSIONAL & CONTINUING EDUCATION (UWPCE) ONLINE REGISTRATION INFO Beginning with registration for Spring 2018, matriculated students in fee-based degree programs offered by UW academic units in partnership with UWPCE (program students) will register online via MyUW. What is changing: * All program students register via MyUW, not UWPCE Registration Services * All courses on PCE time schedule available for enrollment in Registration Period 1 * MyUW will reflect course enrollments in real time * Payment is no longer due at the time of registration, but on the 3rd Friday of the quarter (balance due will generally be available 4 days before the quarter begins) See Payment Procedures for details * Students may add and drop online up until the deadline * All registration and payment-related communications will be sent to students via their UW address * Program students will be automatically opted in to the New MyUW prior to registration for Spring 2018 * MyUW will display each student s schedule in a single view, reducing confusion caused by the old dual system * Students will encounter both UW Continuum College and UWPCE branding during the process * Course waitlists will no longer be managed by UWPCE Registration Services 5

6 What will stay the same: * Fees * Students with holds will be unable to register * All UW Academic Calendar deadlines apply * Add/drop processes after the deadline are unchanged * Students must register themselves; advisors may not do it on their behalf * Program students may use MyPlan for organizing their course schedule, but not to register * Students in state-funded degree programs may register for fee-based courses only through UWPCE Registration Services (not online via MyUW). * Registration by all nonmatriculated students is through UWPCE Registration Services only 6

7 * Registration Period 1: Returning graduate and undergraduate students and postbacs may register for any course on the PCE time schedule only. Integrated Social Sciences students may enroll in designated group-start online courses from the Seattle time schedule using their unique online registration site (not via MyUW). * Registration Period 2: All graduate students may register for any course on any time schedule, unless course- level restrictions are in place. Undergraduate students still restricted to PCE time schedule. How students can get help: * UWPCE How to Register website ( * UWPCE Payment Procedures website ( * Technical support with MyUW: help@uw.edu (UW-IT) * Issues related to balances or payments: c2reg@uw.edu or (UW Continuum College/UWPCE Registration Services) * Questions directed to the UW Registrar will be rerouted to UWPCE Registration Services * Questions about add codes, curriculum, electives: degree program advisor or administrator 7

8 Color blindness: diminished color perception Dichromacy: one of the cone pigments is missing, labeled "first" (prot-, red photoreceptors), "second" (deuter-, green), or "third" (trit-, blue). Anomalous trichromacy: one of the three cone pigments is altered in its spectral sensitivity Protanomaly: altered spectral sensitivity of red receptors, results in poor red green hue discrimination. Deuteranomaly: shift in the green retinal receptors, by far the most common type of color vision deficiency, mildly affects red green hue Color Deficiency Males Females Protanopia 1% 0.01% Deuteranopia 1% 0.01% Protanomaly 1% 0.01% Deuteranomaly 5% 0.4% Overall 8% 0.5% Those with a red/green deficiency will see a 21. If you see nothing, you have rare "total color blindness, inability to distinguish colors. 8

9 Arno G. Motulsky*, July 5, 1923 January 17, interview: Q. AT 84, YOU RE STILL WORKING. WHAT ARE YOU TACKLING IN YOUR LABORATORY? A. One project I m very excited about relates to human color vision. About 8 percent of males have inherited red-green color blindness. This is caused by hereditary abnormalities in color sensitive pigments of the retinal cones in the back of the eyes, which are actually part of the brain. Our laboratory found that one-half of males with normal color vision had the amino acid alanine in their red pigment, while the other half all carried the amino acid serine, at the same site. This finding means that the same exact red color is perceived as a different type of red, depending on a person s genetic makeup. see Vision Research 51 (2011) Q. WHAT S THE POINT OF KNOWING THIS? A. It s exciting to learn that because of heredity, different people can see the same thing differently. I think this may prove useful in studying more complex brain functions. If this were 20 years ago, I d focus on neurogenetics. What s going on in the brain, that s the last frontier. Arno very nearly died at age 16 when he was among the Jewish passengers fleeing Germany on the 1939 voyage of the ill-fated MS St. Louis. After the ship was denied entry to Cuba it was shamefully turned away from the United States. On its return to Europe, Arno s was arrested, ironically, for being German *see depts.washington.edu/medgen/motulsky.shtml

10 Eyeball physiology experiments Seeing retinal blood vessels Hold flashlight near your own closed eyelid and move back and forth - shadows of blood vessels in retina are visible Purkinje images: Hold candle 1 ft from friend's eye, to the side See reflections in successive interfaces 1,2: outer/inner cornea (erect, bright) 3: outer lens (erect, blurry) 4: inner lens surface (inverted - changes as eye focusses) 1 4 Purkinje images from 2 LEDs, 65mm from eye JOSAA

11 More eyeball physiology experiments Blind spot Enlarge this image and stare at + Bring toward face until dot disappears

12 Image persistence Perception experiments Stare fixedly at blue dot in center It will fade away (unless you move your eyes)

13 Blurry blue dot Why? If you do not consciously move your gaze, your eye actually jitters to put scene components on different receptors, to refresh the image Sharp edges remain visible, but brain has a hard time tracking soft edges

14 Perception experiments Complementary-color after-images Stare at the flag 15 sec, then stare at white space You will see a red, white & blue flag See also

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16 Flag Why? When you stare at (for example) a red object, your red-sensitive cones adapt to the light and lose their sensitivity. When you shift your gaze to a white background, you see white (minus red) where the red-sensitive cells have become adapted. White light minus its red component = cyan. Here, we are using colors complementary to the receptor s colors. The result is the same: due to receptor adaptation, you are seeing an absence of (yellow, cyan, black) = (blue, red, white) when you gaze at the white page.

17 Stare fixedly for a minute at one of these pix, then gaze at a piece of white paper, or the wall (or white screen coming up ) 17

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19 Jastrow illusion (A and B are same size) 19

20 Hermann grid illusion (no gray blobs!) 20

21 Hering illusion (horizontals are not curved) 21

22 Ebbinghaus illusion (central circles are same size) 22

23 Land s color vision / physiology experiments See articles by Edwin Land (Polaroid inventor) in Scientific American, 5/1959 and 12/1977 addressing color constancy: Brain can usually perceive a familiar object as being a consistent color regardless of the intensity or wavelengths of light reflecting from it Model: perceived color = proportion of 3 receptors signal strengths but: people can match and identify colors even in unusual illumination situations Land s color perception demonstration: photograph scene through red and green filters onto black and white film project b&w slides through filters We can perceive ~ true colors with only R & G light! how? Land proposed a retinex (retina+cortex) theory of color perception (suggesting both retina and visual cortex are involved in color perception)

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25 Color perception / color constancy Color perception demonstration 2 nd card from the left seems to be a stronger shade of pink in the upper photo than in the lower one. In fact they are the same color (have the same RGB values), but perception is affected by the color of the surrounding areas. [wikimedia: colourillusions2.jpg] Although retinex models are useful in computer vision algorithms, actual human color perception is more complex than Land thought websites for other illusion images shown in class: dragon.uml.edu/psych/illusion.html webexhibits.org/hockneyoptics/post/stork.html 25

26 How many photons do we see? Human eye is an amazing photon detector Sunny day (outdoors): photons per second enter eye (2 mm pupil) Moonlit night (outdoors): photons/sec (6 mm pupil) Moonless night (clear, starry sky) 10 8 photons/sec (6 mm pupil) Light from dimmest star visible to naked eye (mag 6.5): ~1000 photons/sec entering eye Exposure time of retina cells is about 1/8 sec ~100 photons are enough to get a signal to the brain 26

27 Colors Light is characterized by frequency, or more commonly, by wavelength Visible light spans from 400 nm to 700 nm or 0.4 µm to 0.7 µm; mm to mm, etc. 27

28 White light White light is the combination of all wavelengths, with equal representation red hot poker has much more red than blue light experiment: red, green, and blue light bulbs make white RGB monitor combines these colors to display white combined, white light called additive color combination works with light sources blue light green light red light wavelength 28

29 Subtractive colors But most things we see are not light sources Reflection takes away some of the incident light Surface absorbs colors it does not reflect thus the term subtractive color If incident light is white, yellow is absence of blue Subtractive color works with pigments incident white light reflected yellow light (blue gone) blue absorption (e.g., paint, dye) yellow light is made of red and green 29

30 Color perception is complicated Exactly how color perception works still seems subject to discussion Many systems developed to describe and communicate color color wheel Munsell color system 30

31 Colorimetry Artisans and printers have a coordinate system for colors Allows communication of absolute colors, regardless of how well your video screen or printer works! CIE color coordinates = internationally agreed Blackbody colors vs temperature are shown on curve in center White = 6500K (Sun) Pure-color (monochromatic light) wavelengths in nanometers are shown around edges of blob Any color can be described by giving its x-y coordinates Connected with physics as well as physiological and artistic theories of color perception 31

32 Color cube: R,G,B axes 32