1skip chap. 8 for nowChap. 9 – Color (continued)Lecture 19Tuesday, October 26Next time: Chapter 10, start reading.Nov. 2: exam reviewNov. 4: exam II There are computer problems with clicker registration. Be patient.2Ch. 9 - Color• 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 printingWe are hereStart Chapter 10, color perception.3CIE 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. 4White: X = 1/3Y = 1/3Spectral colorwavelengths areat the left and right edgesLess saturated colors are near the centerNon spectral colors are at this edge5Projection (additive) TV systems can only reproduce colors insidethe triangle between the 3 colors of the sources (dots). 6Comparison of old TV phosphors with LEDs (light emitting diodes)7Properties of the CIE diagramThe spectral colors are on the left and right edgesEqual 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.Where is cyan? What’s greatabout this diagram: two numbers, x and y, can be used to describe a color.What’s missingfrom 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.8Alternate diagram: Munsell’s color tree: Hue, value and chromaan alternate way to indicate color that includes brightnessCompare to:9Ink transmission curves400 nm 500 nm 600 nm 700 nm100%Magenta = white – green 10Ink transmission curves400 nm 500 nm 600 nm 700 nm100%Cyan = white – red11Ink transmission curves400 nm 500 nm 600 nm 700 nm100%Yellow ink (unsaturated) = white – blue(contains green, yellow, orange and red)12Additive and subtractive color mixingWhy does one figure have a black interior and the other is white?13Ch. 9 - Color• 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 printingWe are here14Methods of adding colors1. Addition of illumination: stage lighting and 3-color TV projector. Projected colors overlap.2. Partitive mixing: closely spaced dots of colors. TVscreens, laptop screens, pointillist paintings, tight textile weaves, some printing3. 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.15Partitive mixingis placing colors next to one another so that they are merged in the eye.Examples: Pointillist paintingLCD screensOld TV screens (CRT)Plasma TVsDetail from Circus Sideshow (or Parade de Cirque) (1889) showing pointillism Georges Seurat16Georges Seurat, Sunday Afternoon on the Island of La Grande Jatte, 1884-1886, The Art Institute of Chicago.17Sources of light, color balanceColor 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 papers18Color temperatureThe 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 sunlightTungsten 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 bulb19Ch. 9 - Color• 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 printingWe are here20Printing“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 printingadds 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.Recall that inks act like filtersA colored filter subtracts certain colors by absorption and transmits the rest=Incident white lightMagentafiltersubtractsgreenCyanfilter subtractsredOnly bluegetsthrough22Halftone printingHalftones (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 possible23Halftone printing – black and whiteWikipediaSize of dots determines amount of black ink. MagnifiedviewFirst half tone1873Newspapers had 85 lines of dots per inch. 24Halftone printing - colorWhere would I see this? Sunday comics.25Halftone printing - colorThis is the final printed product of adding the 4 above images. WikipediaCyan = -redMagenta = -greenYellow = -blueMagazines use this method. 26Zoom in on a color half tone.27End - Ch. 9 - Color•