1. Color and Blending 03/22/06

2. RGB  Why?  Monitor  Human vision system  Scale: 0-1, 0-n

3. Color in OpenGL  State - all the geometry that is specified after that point will be drawn in the specified color until that color is changed

4. Luminance  Luminance - a color’s intensity, without regard for its actual color.  Important - 10% of people have color perception deficiencies  Interpretation of an image luminance = 0.30*red + 0.59 * green + 0.11*blue

5. HSV   Hue - angles: 0 = red, 120 = green, 240 = blue   Saturation - 0 at the center (no saturation, which makes no real coloring) to 1 at the edge (fully saturated colors)   Value - from 0 at the bottom (no color, or black) to 1 at the top.

6. HLS  Hue and saturation have the same meaning as HSV.  Lightness replaces value - the brightest colors at a value of 0.5.  As colors get lighter, they lose their distinctions of hue and saturation.

7. CMYK   emissive color models, additive color models -- RGB, HSV, HLV  light is emitted to the eye   transmissive color models, subtractive color models   light is reflected to the eye

8. Mach Banding

9. Gamut

10. Color Blending With the Alpha Channel  RGBA - where a  Is called the alpha value  Has a value is a number between 0.0 and 1.0  Is a measure of opacity  Alpha channel was invented to permit image compositing in which an image could be laid over another image and have part of the underlying image show through.  “transparent” should be blended.  transparent colors =~ colored glass: transmissive  Blended colors =~ averaging emissive RGB colors

11.   Idea : Draw opaque objects first.   Given 3 objects above on white background with alpha of.5.   1st object: the frame buffer will have color C1   2nd object: the frame buffer will have color 0.5*C1+0.5*C2   3rd object is drawn on top of the others, the color will be 0.5*C3+0.5*(0.5*C1+0.5*C2), or 0.5*C3+0.25*C2+0.25*C1.   The color of the most recent object drawn is emphasized much more than the color of the other objects.

12. Review alpha.c and alpha3d.c  Sample blending programs  Texture program

13. Stay User Centered   Use appropriate representation for your audience.   Color   Geometry or shapes   Symbolic or synthetic images or pseudo-real images   Relationships between things or the things themselves   Two-dimensional representations, three-dimensional images but with the third dimension used only for impact, and true three-dimensional   Ask your user, your intended audience

14. Image Context   Choosing an appropriate view - staging   Labels - help communicate your problem   Legends - help communicate your encodings

15. Leaving Traces of Motion   Leave something in the frame to show where the parts were in previous frames.

16. Interactions  Keep your images focused  Use appropriate presentation levels for your information.   Use appropriate forms for your information.   Be very careful to be accurate with your display.   Make your interactions reflect familiar and comfortable relationships between action and effect.

17. Cultural Context of the Audience Associations of Colors by Professional Group ColorProcess Control Engineers Financial Managers Health Care Professionals BlueCold WaterCorporate Reliable Death Turquoise (Cyan) SteamCool SubduedOxygen deficient GreenNominal SafeProfitableInfected YellowCautionImportantJaundiced RedDangerUnprofitableHealthy PurpleHotWealthyCause for concern

18. Context-sensitive Color

19. Accuracy   Visualizations should help the user understand information clearly and accurately.   present the data or theory you have as accurately as possible.   making attractive images is useful when you can, even if your goal is accuracy   Garbage in, garbage out   Example:   If you do not know a priori that there is a smooth variation to the population from which you get your data, then you need to present the data as discrete values and not use smooth interpolations or smooth shading to make your data look smoother.

20. Homework  Tonight: What is your project? What information do you need to progress?  Homework for next week  Work on your project.  Turn in another revision next week. This will not be graded except to make sure there is a change from this week’s code.  Read chapter 7  Quiz - should next week’s quiz be rescheduled?