Take a break: Watch some stop-motion animation Music: Grindin http://vimeo.com/9625370 1 skip chap. 8 for now Chap. 9 Color (continued) Lecture 18 Thursday, March 11 Next week: Chapter 10, start reading. March 30: exam review April 1: exam II BA 2
Ch. 9 - Color We are here Spectral and non-spectral colors Intensity distribution curve Intensity, hue, saturation Additive primaries: R, G. B. Subtractive primaries: C, M, Y Hair, skin, and eye color CIE diagram Lighting, painting and printing 3 Color in plants and animals Chlorophyll reflects green and absorbs red and blue. The reflected green is not being used. So it is clear that green is NOT the best color of light for growing plants. Carotenoids are a class of compounds that color carrots, tomatoes, corn, and peppers. Some animals absorb this coloring from plants and become orange themselves, such as lobsters and flamingos. Autumn colors occur when the chlorophyll decays leaving behind the more brightly colored carotenoids. Anthocyanin is another plant color that is often magenta, containing both red and blue. For example, eggplants, some cabbages, and berries contain anthocyanin. Myoglobin, a compound that stores oxygen, is in red meat. "Dark meat" such as chicken legs or hearts, contains more myoglobin. These muscles are used constantly. The breast muscle of chicken is rarely used for flying, and thus is lighter, containing less myoglobin. 4
Hair, skin, and eye color 1. Your pigment is melanin. You have 2 forms pheomelanin (yellow/red) eumelanin (black and brown subtypes) Albino persons = no pigment at all There are additional genes (more than one) affecting how much we have of each kind. 2. The signaling gene has 300 amino acids in the DNA sequence. There are many variations. Variations produce red hair, blonde, auburn, strawberry blonde, etc. 5 Skin color and evolution Sunlight creates vitamin D. Europe = less sunlight = less vitamin D Light skin (less melanin) is an advantage. Other chemicals (folate) are broken down by sunlight. Equator = more sunlight = more folate loss Dark is an advantage. (Skin cancer occurs to late in life to affect survival.) Ability to tan: Is also inherited. Red haired people do not tan. 6
Eye color Small amount of pigment = blue eyes. Tiny particles (cells) in the eye scatter blue better, like the atoms that scatter blue light from the sky or from the swimming pool. Pigment hides the blue. More eumelanin pigment = brown eyes. Less brown pigment = hazel, green, etc. 7 Hair color Eumalinin colors hair brown or black. Pheomelanin colors hair red in small quantities, black in large quantities. And makes freckles. Low amounts of either results in blonde or strawberry blonde. Gray occurs with aging as melanin production stops in the hair follicle. 8
Ch. 9 - Color We are here Spectral and non-spectral colors Intensity distribution curve Intensity, hue, saturation Additive primaries: R, G. B. Subtractive primaries: C, M, Y Hair, skin, and eye color CIE diagram Lighting, painting and printing 9 CIE diagram (International Commission on Illumination) This is a color triangle with Green at the top, Blue at lower left, Red at (lower) right x,y positions on the color triangle represent all the colors that can be reproduced by adding red, green and blue. Limitation: darkness is missing. To be complete you must also specify lightness or brightness. 10
White: X = 1/3 Y = 1/3 Less saturated colors are near the center Spectral color wavelengths are at the left and right edges Non spectral colors are at this edge 11 Projection (additive) TV systems can only reproduce colors inside the triangle between the 3 colors of the sources (dots). 12
Comparison of old TV phosphors with LEDs (light emitting diodes) 13 Properties of the CIE diagram The spectral colors are on the left and right edges Equal mixing of two spectral colors on the edge makes the color half way between these two colors (on the line joining the two colors.) Where is magenta on the diagram? It is half way across the bottom, which is an equal mixture of red and blue. What s great about this diagram: two numbers, x and y, can be used to describe a color. What s missing from the C.I.E. diagram? Because the colors are adjusted to add to 100%, dark colors (that total less than 100%) aren t represented, for example, black and brown. 14
Alterbate diagram: Munsell s color tree: Hue, value and chroma an alternate way to indicate color that includes brightness Compare to: 15 Ink transmission curves Magenta = white green 100% 400 nm 500 nm 600 nm 700 nm 16
Ink transmission curves Cyan = white red 100% 400 nm 500 nm 600 nm 700 nm 17 Ink transmission curves Yellow ink (unsaturated) = white blue (contains green, yellow, orange and red) 100% 400 nm 500 nm 600 nm 700 nm 18
Additive and subtractive color mixing Why does one figure have a black background and the other is white? 19 Concept Question: Cheat sheet 20
Concept Question: Cheat sheet 21 Concept Question: Cheat sheet
Concept Question: Cheat sheet Concept Question: Cheat sheet
Concept Question: White is an equal mixture of red, green and blue. What is another metamer for white light? A. Red and cyan; B. Cyan, magenta and yellow; C. Blue and yellow; D. A,B, and C No cheat sheet Ch. 9 - Color We are here Spectral and non-spectral colors Intensity distribution curve Intensity, hue, saturation Additive primaries: R, G. B. Subtractive primaries: C, M, Y Hair, skin, and eye color CIE diagram Lighting, painting and printing 26
Methods of adding colors 1. Addition of illumination: stage lighting and 3-color TV projector. Projected colors overlap. 2. Partitive mixing: closely spaced dots of colors. TV screens, laptop screens, pointillist paintings, tight textile weaves, some printing 3. Time mixing: a rotating color wheel. It s hard to find examples. 4. Binocular mixing: different color to each eye. The colors "blend" in the brain. 27 Partitive mixing is placing colors next to one another so that they are merged in the eye. Examples: Pointillist painting LCD screens Old TV screens (CRT) Plasma TVs Detail from Circus Sideshow (or Parade de Cirque) (1889) showing pointillism Georges Seurat 28
Georges Seurat, Sunday Afternoon on the Island of La Grande Jatte, 1884-1886, The Art Institute of Chicago. 29 Sources of light, color balance Color balance important for movies and stage lighting. White light should contain equal amounts R, G and B but often does not. Examples of odd (unbalanced) lighting: Candles and campfires contain an excess of red. So do sunsets and tungsten bulbs. Some street lamps (low pressure sodium, for example) contain only a few wavelengths. All other colors are missing. When red is missing, red lipstick looks black. Demo: blue light with red, white, and blue papers 30
Color temperature The temperature of light bulb determines the relative amount of red. Cooler bulbs have more red than hotter bulbs. A lamp can be characterized by its temperature Sun, 5000 K (has a lot of blue) Photoflood lamp, 3200 K, an approximation of sunlight Tungsten lamp, 2850 K, looks orange, less blue. Candle, 1800 K, distinctly red, almost no blue. Color film is balanced for daylight. Photos made by candlelight or ordinary tungsten lamps will look unnaturally red. Demo: blue and red filter with dimmed bulb 31 Printing Ink jet printers use four inks: cyan, magenta, yellow, and black. These are often called CMYK printers, with K for black. Ink on the paper acts as a filter for light reflected from paper. Combinations of C, M, and Y can make all colors by filtration. Black is needed for darker blacks. High brightness paper is needed for good pictures. Six color printing adds additional inks to CMYK. Some use red and blue, others use light cyan and light magenta. Canon has an 11 ink printer. Watercolors work the same way. Putting on more results in more light being absorbed, so a brighter blue requires less watercolor and a darker one more. 32
Recall that inks act like filters A colored filter subtracts certain colors by absorption and transmits the rest = Incident white light Magenta filter subtracts green Cyan filter subtracts red Only blue gets through Colored surfaces subtract certain colors by absorbing them, while reflecting others White in Magenta out White in Green out Magenta surface absorbs (subtracts) green. Green surface absorbs (subtracts) red and blue (magenta).
Halftone printing Halftones (black and white): The printing plate is covered with dots of different size with the bigger dots putting more ink than the smaller dots. Halftones (color) There is a different halftone printing plate for each of the subtractive primaries. High quality color printing (National Geographic, art books) use more than four inks. Print resolution is measured in dots per inch. More dots/inch = more detail. Typical inkjet: 600 dots per inch but 1200 to 4800 dots per inch (dpi) is possible 35 Halftone printing black and white Size of dots determines amount of black ink. Newspapers have 85 lines of dots per inch. Wikipedia Magnified view First half tone 1873 36
Halftone printing - color Where would I see this? Sunday comics. 37 Halftone printing - color Cyan = -red Magenta = -green Yellow = -blue This is the final printed product of adding the 4 above images. Wikipedia 38