Our Plans

1. Our Plans • Today: Review of material for the exam (chapters 9,10,&13) • Dec. 14: Exam 3 grades posted; • Dec. 15: Final grades posted; • Exam: • Multiple choice questions; • Problems (2-3 per chapter); • Information/preparation: • http://www.colorado.edu/physics/phys1230/phys1230_fa11/Exams.htm • Practicing problems; • Reading Material; • Solutions will be posted on the web page soon after the exam;

2. Here is an intensity distribution curve which gives us the sensation of yellow Here is a different intensity distribution curve which also gives us the same sensation of yellow The two colors described by the two different intenstiy curves are called metamers The same color sensation can often be produced by 2 or more differentintensity distribution curves

3. Color tree (e.g. Fig. 9.5 in book) Moving up the tree increases the lightness of a color Moving around a circle of given radius changes the hue of a color Moving along a radius of a circle changes the saturation (vividness) of a color These three coordinates can be described in terms of three numbers Photoshop: uses H, S and B hue lightness saturation Hue, Saturation and Brightness (HSB): One way to use 3 numbers to specify a color instead of using an intensity-distribution curve

5. In addition to using Hue, Saturation and Brightness (HSB); Many (but not all) colors can be described in terms of the relative intensities of a light mixture of a certain wavelength red, wavelength green and wavelength blue lights 650-nm red 530-nm green 460-nm blue These are called the additive primaries The mixing of the additive primaries is called additive mixing Additive mixing is usually done by mixing primary color lights with different intensities but there are other ways to be discussed later Demonstrate with Physics 2000 Red, greenandblue(RGB): RGB is another way to use 3 numbers to specify a color instead of using an intensity-distribution curve or HSB http://www.colorado.edu/physics/2000/tv/colortv.html yellow 650-nm red 530-nm green magenta cyan 460-nm blue

6. Definition of complementary color (for additive mixtures): The complement of a color is a second color. When the second color is additively mixed to the first, the result is white. Blue & yellow are complementary B + Y = W. Green & magenta are complementary G + M = W Cyan and red are complementary C + R = W Magenta is not a wavelength color— it is not in the rainbow There is at most one wavelength complementary color for each wavelength color (Fig 9.9) yellow red green magenta cyan blue Complementary additive colors white

7. Additive mixing of colored light primaries Blue added to green = cyan. Green added to red = yellow. Red added to blue = magenta.

8. Complementary colored lights(additive mixing) Blue (primary) and yellow. Green (primary) and magenta. Red (primary) and cyan.

9. The chromaticity diagram is in many ways similar to a color tree A chromaticity diagram has a fixed brightness or lightness for all colors Wavelength colors are on the horseshoe rim but non-wavelength colors like magenta are on the flat part of the rim Inside are the less saturated colors, including white at the interior less saturated colors saturated wavelengthcolors saturated non-wavelengthcolors Chromaticity diagrams: Yet another way to represent colors by (3) numbers

10. The numbers that we use to identify a color are its x-value and y-value inside the diagram and a z-value to indicate its brightness or lightness x and y specify the chromaticity of a color Example: Apple pickers are told around the country that certain apples are best picked when they are a certaim red (see black dot) Since the chromaticity diagram is a world standard the company can tell its employees to pick when the apples have chromaticity x = 0.57 y = 0.28 The "purest" white is at x = 0.33 and y = 0.33 Chromaticity diagram can be related to colors in Photoshop Using the chromaticity diagram to identify colors

11. An additive mixture of two wavelength colors lies along the line joining them Example: The colors seen by mixing 700 nm red and 500 nm green lie along the line shown Where along the line is the color of the mixture? Answer depends on the relative intensities of the 700 nm red and the 500 nm green. Here is what you get when the green is much more intense than the red (a green) Here is what you get when the red is much more intense than the green (a red) Here is what you get when the red is slightly more intense than the green (a yellow) Using the chromaticity diagram to understand the result of additive mixing of colors Note — this works for addingtwo colors in middle also!

12. The complement to any wavelength color on the edge of the chromaticity diagram is obtained by drawing a straight line from that color through white to the other edge of the diagram Example: The complement to 700 nm red is 490 nm cyan Example: The complement to green is magenta - a non-wavelength color Using the chromaticity diagram to understand complementary colors

13. To find the dominant hue of the color indicated by the black dot Draw st. line from white through the point to get dominant wavelength, and hence, hue (547 nm green) Works because additive mixture of white with a fully-saturated (wavelength) color gives the desaturated color of the original point Using the chromaticity diagram to find the dominant hue of a color in the interior of the diagram

14. Partitive mixing is another kind of additive color mixing but not achieved by superimposing colored lights! Instead, it works by putting small patches of colors next to each other. From a distance these colors mix just as though they were colored lights superimposed on each other Examples: Seurat pointillism Color TV and computer screens (Physics 2000) Photoshop example What is partitive mixing?

16. Cyan filter subtracts red Yellow filter subtracts blue A colored filter subtracts colors by absorption. = Incident white light Only green gets through

17. = Magenta filter subtracts green Cyan filter subtracts red A colored filter subtracts certain colors by absorption and transmits the rest Incident white light Only blue gets through

18. Magenta filter subtracts green Yellow filter subtracts blue A colored filter subtracts colors by absorption. = Incident white light Only red gets through

20. Rules for combining the subtractive primaries, cyan, yellow and magenta: White light passed through a cyan filter plus a magenta filter appears blue White light passed through a yellow filter plus a magenta filter appears red White light passed through a yellow filter plus a cyan filter appears green Why? What is the effect of combining (sandwiching) different colored filters together? cyan yellow magenta

21. Colored surfaces subtract certain colors by absorbing them, while reflecting others White in White in Green out Magenta out Magenta surface absorbs (subtracts) green. Green surface absorbs (subtracts) red and blue (magenta).

22. Green light on a magenta surface appears colorless because green is absorbed Magenta light on a green surface appears colorless because magenta is absorbed Magenta in Green in No color No color Magenta surface absorbs (subtracts) green. Green surface absorbs (subtracts) red and blue (magenta).

23. • Rule: Multiply the intensity-distribution of the light source by the reflectance of the colored object to get the intensity distribution of the the illuminated object • Example: Look at a magenta shirt in reflected light from a Cool White fluorescent tube. • It appears grey (colorless) Confirm by multiplying the intensity distribution curve by the reflectance curve to get the new intensity distribution curve for the reflected light When looking at a colored object in a colored light source what is the resulting color? Cool white fluorescent bulb Magenta shirt this number This number times How the shirtappears in this light equals this number You multiply the two y-valuesat each x to get the new curve

24. Halftone • Left: Halftone dots. • Right: How the human eye would see this sort of arrangement from a sufficient distance or when they are small. • Resolution: measured in lines per inch(lpi) or dots per inch (dpi); for example, Laser Printer (600dpi)

25. Color halftoning Printer's ink Paper beneath Three examples of color halftoning with CMYK separations. From left to right: The cyan separation, the magenta separation, the yellow separation, the black separation, the combined halftone pattern and finally how the human eye would observe the combined halftone pattern from a sufficient distance.

26. Demonstration

27. Color Liquid Crystal Displays (LCDs)

28. s-cones absorb short wavelength light best, with peak response at 450 nm (blue) L-cones absorb long wavelength light best, with peak response at 580 nm (red) i-cones absorb intermediate wavelengths best, with peak response at 540 nm (green) Light at any wavelength in the visual spectrum from 400 to 700 nm will excite these 3 types of cones to a degree depending on the intensityat each wavelength. Our perception of which color we are seeing (color sensation) is determined by how much S, i and L resonse occurs to light of a particular intensity distribution. Rule: To get the overall response of each type of cone, multiply the intensity of the light at each wavelength by the response of the cone at that wavelength and then add together all of the products for all of the wavenumbers in the intensity distribution L-cones i-cones s-cones Spectral response of cones in typical human eye relative response Chapter 10: We have three different kinds of cones whose responses are mainly at short, intermediate and long wavelengths

29. Our sensation of color depends on how much total s, i & L cone response occurs due to a light intensity-distribution Multiply the intensity distribution curve by each response curve to determine how much total S, i, and L response occurs We experience the sensation white when we have equal total s, i & L responses There are many ways this can occur!! E.g., when broadband light enters our eye Another way to experience white is by viewing a mixture of blue and yellow E.g., 460 nm blue of intensity 1 and 575 nm yellow of intensity 1.66 The blue excites mainly s-cones but also a bit of i-cones and a bit of L-cones The yellow excites i-cones and (slightly more) L-cones but no s-cones The result is an equal response of s-cones, i-cones and L-cones (details) Spectral response of cones in typical human eye 575 nm yellow of intensity 1.66 relative response Examples of two different ways we see white 1.66 460 nm blue of intensity 1 1 0

30. Our sensation of yellow depends on a special s, i & L cone response We experience the sensation yellow when 575 nm light reaches our eyes What really gives us the sensation of yellow is the almost equal response of i and L cones together with no s-cones!! Another way to experience yellow is by seeing overlapping red & green lights E.g., 530 nm green of intensity 1 and 650 nm red of intensity 2.15 The green excites mainly i-cones but also L-cones, while the red excites mainly L-cones but also i-cones The total respone of s & i-cones due to the spectral green and red is the same as the total response due to spectral yellow In general need 3 wavelength lights to mix to any color Spectral response of cones in typical human eye relative response How does a normal person see yellow when only red and green lights are superimposed? 650 nm red of intensity 2.15 2.15 575 nm yellow of intensity 1.35 530 nm green of intensity 1 1 0

31. All of the hues can be named qualitatively by how much green, red, blue or yellow is "in" them We don't need orange, purple or pink: orange can be thought of as yellow-red purple can be thought of as red-blue pink has the same hue as red but differs only in lightness We can break up the diagram into 4 different regions by drawing two lines whose endpoints are the psychological primary hues The endpoints of the yellow line are 580 nm "unique" yellow and 475 nm "unique" blue One endpoint of the red line is 500 nm "unique" green and the other is "red" (not unique or spectral - really more like magenta) We can verify color namingof hues in terms of the psychological primaries on the chromaticity diagram Greenness & yellowness Greenness & blueness Redness & yellowness Redness & blueness

32. Viewing a progression of colors in the direction of the yellow line from 475 nm blue towards 580 nm yellow, we see more yellowness of each color and less blueness. We call this perception our y-b channel Yellow & blue are opponents Moving parallel to the red line from 500 nm green towards nonspectral red we see more redness in each color and less greenness. We call this perception our r-g channel Red and green are opponents The lines cross at white, where both y-b & r-g are neutralized What is meant by the opponent nature of red vs green (r-g) perception and of yellow vs blue (y-b) perception. Greenness & yellowness r-g Greenness & blueness Redness & yellowness y-b Redness & blueness

33. The 3 kinds of cones are related to r-g and y-b by the way they are connected to neural cells (such as ganglion cells) Cones of each kind are attached to 3 different neural cells which control the two chromatic channels, y-b and r-g,and the white vs black channel called the achromatic channel (lightness) "wiring" is the following: When light falls on the L-cones they tell all 3 neural cells to increasethe electrical signal they send to the brain When light falls on the i-cones they tell the r-g channel cell to decrease (inhibit) its signal but tell the other cells to increase their signal When light falls on the s-cones they tell the y-b channel cell to decrease (inhibit) its signal but tell the other cells to increse their signal + + + + +  + +  neural cellfor w-blkachromaticchannel How might the three types of cones be "wired" to neural cells to account for our perception of hues in terms of two opponent pairs of psychological primaries r-g and y-b? s-cone i-cone L-cone neural cellfor y-bchromaticchannel neural cellfor r-gchromaticchannel Electrical signal to brain

34. Theneural cell for the y-bchromaticchannel has its signal inhibited when (bluE) light excites the s-cone INTERPRETED AS BLUE enhanced when light excites the i & L cones INTERPRETED AS YELLOW Theneural cell for the r-gchromaticchannel has its signal inhibited when (green) light falls on the i-cone INTERPRETED AS GREEN enhanced when light excites the s and L coneINTERPRETED AS MAGENTA (Psychological red) The neural cell for the achromatic channel has its signal enhanced when light excites any of the cones + + + + How can this "wiring" work to produce the chromatic channels? s-cone i-cone L-cone + + +   neural cellfor y-bchromaticchannel neural cellfor r-gchromaticchannel neural cellfor w-blkachromaticchannel Electrical signal to brain

35. Monochromacy (can match any colored light with any 1 spectral light by adjusting intensity) Either has no cones (rod monochromat) or has only 1 of the 3 types of cones working (cone monochromat). Sees ony whites, greys, blacks, no hues Dichromacy (can match any colored light with 2 spectral lights of different intensities of (rather than the normal 3) L-cone function lacking = protanopia i-cone function lacking = deuteranopia s-cone function lacking = tritanopia no y-b channel but all 3 cones OK = tetartanopia Anomalous trichromacy (can match any colored light with 3 spectral lights of different intensities as in normal vision, but still have color perception problems) Protanomaly Shifted L-cone response curve Deuteranomaly (most common) Shifted i-cone response curve Confusion between red and green. Tritanomaly Yellow-blue problems: probably defective s-cones Neuteranomaly ineffective r-g channel Systematic description of color-blindness (no need to memorize terminology)

36. 2 different ways toINCREASEthe signal the ganglion cell sends to brain Red light falling on cones in center of receptive field attached to ganglion cell Green light on surround 2 different ways todecreasethe signal the ganglion cell sends to the brain Red light on surround Green light on center Electrical signal to brain from ganglion cell is at ambient level when no light is on center or surround When signal to brain is INCREASEDwe interpret that as red When signal to brain is decreased we interpret that as green Receptive field of a double-opponent cell of the r-g type signal to brain

37. A double-opponent cell differs from a single opponent cell In both of them R in the center increases the signal In a single-opponent cell G in surround would inhibit signal, whereas in double-opponent cell G enhances In a double-opponent cell R in center enhances signal (ganglion cell signals red) G in surround enhances signal (ganglion cell signals red) R in surround inhibits signal (ganglion cell signals green) G in center inhibits signal (ganglion cell signals green) We can summarize this by just showing the center & surround of the receptive field and indicating the effect of red (R) and green (G) on each Fictional cell real cell

38. How do 3D movies use polaroid filters?