Summary of the material to be tested in

Summary of the material to be tested in the exam #2: Chapters 4 -7 • Ch. 4: Cameras photography • Exam: • How cameras work; • camera settings; • Taking good pictures; • • • Ch. 5: Human Eye & Vision • Eye & camera: similarities & differences • How eye works & how image is formed; • Ch. 6: Optical instruments & vision correction • Vision problems and correction; • How eyeglasses & optical lenses work; • Microscope and magnifying glass; • Telescopes; • Ch. 7: Image processing by eye • Lateral inhibition & temporal response; • Illusions & afterimages. 11 multiple choice questions; Problems (2 -3 per chapter); 1 Extra-credit problem. Nothing on Chapter 9 (color) • Information/preparation: http: //www. colorado. edu/physics/phys 1230_fa 08/Exams. htm • • • Exam assignment/solutions from 2007; Practicing problems: find answers; Reading Material; Help: additional office hours (F-521); Solutions will be posted on the web page soon after the exam; 1

An example of a possible exam question:

An example of a possible exam question: • The instructor has eyeglasses • Teaching assistant wears of lens power -1. 5 D. Will he eyeglasses of lens power be able to see a student 2 D. He came to do exam cheating in the opposite part proctoring but forgot his of our lecture room? eyeglasses. Will he be • A. Yes; able to see a student • B. No. cheating in the opposite part of our lecture room? • What if he forgets to bring his eyeglasses? • A. Yes; • B. No.

Chapter 8: Binocular vision & perception of depth: we skip this chapter now, but will learn the main points later (3 D movies, etc. )

Physics 1230: Light and Color Chapter 9 (with some material from Chapter 8) • Chapter 9: Color • How to identify and classify color • Wavelength colors • Intensity distribution curve • Hue, saturation and brightness • "Color tree" or "cylinder" • Chromaticity diagrams and how to use them • What happens when you add colored lights together (additive mixing)? • Additive primaries (RGB) • Spectral complements • Partitive mixing of colored dots: TV • How do color filters work (subtractive mixing) • Water colors & printers inks • Paints and pigments 5

What are spectral colors? Violet Blue Green Yellow Orange Red 400 nm 460 nm 530 nm 575 nm 600 nm 650 nm • Spectral colors are the color sensations we perceive in a rainbow or spectrum of a prism • Demo with prism • Other names for spectral colors • Wavelength colors (because they each can be identified by one and only one wavelength) • Monochromatic colors (mono means one, chromos means wavelength color) • Examples: 650 nm red, 530 nm green, 460 nm blue Infrared • We are able to distinguish more than a million different colors • Most colors that we see are not spectral colors. Examples: • White • Pink • Brown

Most colors that we see are mixtures of spectral (wavelength) colors. • In order to specify a mixture of wavelength colors we need to describe how much of each one is present in the mixture • The best way to do this is to plot a curve - the intensity-distribution curve • Each point on the horizontal axis is a different wavelength color • The vertical distance of the curve from x-axis tells us how much of that wavelength color is present in the mixture! • You would see the intensity distribution if you passed this light through a prism! • A pure spectral color would have an intensity distribution curve consisting of only one vertical line (at its wavelength) • This is the intensity-distribution curve of light from a White fluorescent tube • Most colors can be described by a (different) intensity-distribution curve

Intensity distributions for color filters

How we characterize colors: Hue, Saturation and Brightness (HSB, recall photoshop): what they mean in terms of intensity distribution curves? • Hue is specified by the dominant wavelength color in the intensitydistribution curve • Saturation is the purity of a color (absence of other wavelengths). • The pure spectral colors are the most saturated • Brightness refers to the sensation of overall intensity of a color Brightness Bright white Grey Black Hue Saturation Desaturatated orange = saturated Brown (same) orange + white Orange Blue

The same color sensation can often be produced by 2 or more different intensity distribution curves • • • 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

How is a reflectance curve different from an intensity distribution curve? magenta shirt • Reflectance curve tells us how effectively part of a surface (a shirt, a part of a picture, a car, etc) reflects light of different wavelengths • Reflectance curve of a magenta shirt (1 = 100%) • Light and dark in terms of reflectance curves Light area in a black and white picture Dark area in a black and white picture

Earth-orbiting satellites take pictures of Earth at different wavelengths to determine the health of crops and water

Hue, Saturation and Brightness (HSB): One way to use 3 numbers to specify a color instead of using an intensity-distribution curve • Color tree (e. g. Fig. 9. 5 in book) • Photoshop: uses H, S and B hue saturation lightness • 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

Continue Learning about perception of Color and color mixing

Exam # 2 was & extra credit assignments • • • A. Trivial B. Relatively easy; C. Appropriate; D. Difficult; E. Overwhelmingly difficult; • A. I will do extra credit projects to improve my grade (20 points/project); • B. I will not do extra credit projects;

Clicker Registration, etc. • 8 students have not registered clickers!!! • Clicker grades will be updated by Monday. • Exam grades will be posted before Monday morning.

Red, green and blue (RGB): RGB is another way to use 3 numbers to specify a color instead of using an intensity-distribution curve or HSB • • 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 http: //www. colorado. edu/physics/ 2000/tv/colortv. html 530 -nm green cyan yellow 650 -nm red magenta 460 -nm blue

Complementary additive colors • 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 green white cyan magenta blue red

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

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

Chromaticity diagrams: Yet another way to represent colors by (3) numbers • 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 wavelength colors saturated non-wavelength colors

Different lightnesses are on other chromaticity diagram "slices" along the trunk of a chromaticity "tree" saturation color tree Lightness (z) hue Chromaticity "tree" 3 numbers (x, y, z) specify a color y x hue saturation

We will now learn the many uses of a chromaticity diagram • To identify colors with three numbers • To predict the results of additive mixing • To understand complementary colors • To find the dominant hue of a color

Using the chromaticity diagram to identify colors • • 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 understand the result of additive mixing of colors • 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) Note — this works for adding two colors in middle also!

Using the chromaticity diagram to understand complementary colors • 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 nonwavelength color

Using the chromaticity diagram to find the dominant hue of a color in the interior of the diagram • 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

What is partitive mixing? • 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

Subtractive mixing It is a common misconception that a filter or an apple adds color to white light! • Examples: • A color filter or colored object takes • Think of white light as a mixture of away certain wavelengths present in red, green and blue wavelengths white light by absorbing them • An apple is red because when white • When light passes through a color filter light shines on it it absorbs (subtracts) or reflects from a colored object, 3 things blue and green wavelengths and can happen to the components of the light reflects red wavelengths at each wavelength • Transmission (light of a particular wavelength goes through and comes out the other side) • Reflection (a particular wavelength is reflected) • Absorption (a particular wavelength is soaked up by the filter or object and neither reflects nor is transmitted) • Generally, different things happen at different wavelengths in the composition of the light for any particular filter or colored object • A colored filter is red because when white light shines on it absorbs (subtracts) blue and green wavelengths and transmits red wavelengths • Superimposing filters and letting light go through the combination gives a very different result from superimposing the light passing through each of those filters separately

Color Filters

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

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

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

Exam #2: Statistics/Results/Grades • Problems with grading: can be corrected within one week; C-, C, C+ B-, B, B+ AA A

Exam # 2 was & extra credit assignments • • • A. Trivial B. Relatively easy; C. Appropriate; D. Difficult; E. Overwhelmingly difficult; • Extra credit projects to improve the grade (20 points/project);

Plans for Today • Plans: Finish Chapter #9 & • Demo on work of Displays continue with Chapter #10; and printers: use a microscope to see how different colors are • Final Grade: Clicker obtained; questions – 5%; HWs – • Demo on spectral 20%; Exams – 75%; dependence of light coming from the display screen;

Clicker Registration, etc. • 7 students have not registered clickers!!! • Clicker grades will be updated by Thursday.

Demonstration

What is the effect of combining (sandwiching) different colored filters together? • 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? cyan yellow magenta

A few words about the subtractive primaries cyan, yellow and magenta § Yellow is perceived in a very narrow band of wavelengths from 575 to 580 nm on the right edge of the horseshoe. § Cyan is perceived in a band of wavelengths from roughly 482 nm to 492 nm on the left edge of the horseshoe. § Magenta and its neighboring colors on the bottom straight part of the horseshoe cannot be found in the spectrum at any wavelength. Transmission distribution of filters • However, in practice, any colored paper, picture, fabric or filter which is yellow or cyan is never a pure spectral color § Yellow, in practice, is always an additive mixture of the spectral green & red on either side of wavelength yellow § Cyan, in practice, is always an additive mixture of spectral blue & green on either side of wavelength cyan. Cyan is an additive mixture of mostly blues and greens Yellow is an additive mixture of mostly reds and greens

A transmittance curve shows what percent of each of the wavelengths in white light go through a filter • A transmittance curve shows what percent of each of the wavelengths are transmitted through this magenta filter Transmittance Reflectance • Just as a reflectance curve shows what percent of each of the wavelengths in white light reflect from this magenta surface

Non-ideal colored filter subtracts colors by absorption. Incident white light Non-ideal reddish filter subtracts some green and blue Transmittance 100% Non-ideal yellow Orange-yellow filter subtracts some gets blue, red and green through Transmittance 100% 400 500 600 700 Wavelength

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

oc N Magenta surface absorbs (subtracts) green. or lor o Magenta in co l Green in Magenta light on a green surface appears colorless because magenta is absorbed N o Green light on a magenta surface appears colorless because green is absorbed Green surface absorbs (subtracts) red and blue (magenta).

More examples of colored objects viewed under light which is not white • Colored clothes or other colored object may change their apparent color and apparent lightness when viewed under light which is not white • What does yellow look like under blue light? • What does blue look like under blue light? • What does yellow look like under yellow light? • What does blue look like under yellow light? • How can you predict the resulting color if you know • the intensity distribution of the light source and • the reflectivity of the colored clothes or other colored objects which are illuminated by that light source? • Next slide explains how to do this

When looking at a colored object in a colored light source what is the resulting color? • Rule: Multiply the intensity-distribution of the light source by the reflectance of the colored object to get the intensity distribution of 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 Cool white fluorescent bulb This number times How the shirt appears in this light equals this number Magenta shirt this number How on earth do you multiply two curves? You multiply the two y-values at each x to get the new curve

Printer's inks • • • Reflected ray from top layer of printer's ink mixing additvely with transmittedreflected-transmitted rays Magazine and newspaper images use subtractive mixing of cyan, magenta, yellow and black inks (CMYK color) plus the halftone process, which breaks up images into dots or other patterns • • The smaller the black dots the lighter the grey This enables additive mixing of the colored dots with each other and with the white paper to produce the lighter less saturated colors other than CMYK Printer's ink Paper beneath

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 (600 dpi)

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.

Demonstration

Color Liquid Crystal Displays (LCDs)

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