lecture3 color representation in computer graphics(Computer graphics tutorials)
Download as PPT, PDF•1 like•1,580 views
The document provides an overview of color representation in computer graphics, focusing on additive and subtractive models, the standard CIE chromaticity, and the principles of human color perception. It explains the tri-stimulus representation using red, green, and blue as primary colors and discusses how colors can be created or matched through varying the intensity of these components. Additionally, it highlights the practical aspects of color display calibration for accurate representation on monitors.
lecture3 color representation in computer graphics(Computer graphics tutorials)
- 1. CSC 406: Applied Computer Graphics Lecture 3: Color Representation in computer graphics.
- 2. Daroko blog Do Not just learn computer graphics an close your computer tab and go away.. APPLY them in real business, Visit Daroko blog for real IT skills applications,androind, Computer graphics,Networking,Programming,IT jobs Types, IT news and applications,blogging,Builing a website, IT companies and how you can form yours,
- 3. Color Representation:Color Representation: Scope: Introduction. Additive and subtractive models. The standard CIE chromaticity.
- 4. Color Representation: Color is visible light between 400nm and 700nm. Visible light frequencies range between ... Red = 4.3 x 1014 hertz (700nm) Violet = 7.5 x 1014 hertz (400nm) Humans have trichromatic color vision Three color values
- 6. Color Representation… In the eye we have just three distinct 'cone' cells for detecting light energy. These respond to a band of wavelength centered around red (600), green (560) and blue (440); respectively. The bands overlap, so, for example green light excites all three types.
- 7. The consequence of this is that each type of cell may be excited similarly from very different energy distributions Any distribution of wavelengths will be perceived by us as a single color, but two entirely different distributions of intensities could be perceived as the same color.
- 8. In order to match a color, we can adjust the brightness of 3 overlapping primaries until the two colors look the same. C = color to be matched RGB = laser sources (R=700nm, G=546nm, B=435nm) Selecting three pure light sources (R, G, B) and mixing them together while varying their respective intensities, one may be able to create a large number of colors.
- 9. Each color satisfies the following linear combination: X = r*R + g*G + b*B where r, g, b are intensities of the red, green and blue light sources. Not all colors can be matched in this way. However, by adding one of the pure colors to an unknown unmatchable color, we can make a match.
- 10. This is in effect subtracting a color from the mix. X + r*R = g*G + b*B or X + g*G = r*R + b*B or X + b*B = r*R + g*G
- 11. The representation of colors as a mixture of three components is called the tri-stimulus representation; very commonly used in monitors and other active color devices. The pure colors used are red, green and blue, and are referred to as the additive primary colors.
- 17. The human eye can distinguish hundreds of thousands of different colors. When two colors differ only in hue, the wavelength between just noticeably different colors varies with the wavelength! More than 10 nm at the extremes of the spectrum Less than 2 nm around blue and yellow Most JND hues are within 4 nm. Altogether, the eye can distinguish about 128 fully saturated hues Human eyes are less sensitive to hue changes in less saturated light (not a surprise)
- 18. Complementary colors: White represents the presence of all three colors – in equal quantities. Black represents the absence of the three colors. Two colors are said to be complementary if their mix gives white. A color can be generated by either: Adding the primary colors – R, G, and B Removing their complimentary colors.
- 19. The additive color model:The additive color model: Red, green and blue are the additive primaries. Colors can be generated by adding the additive primaries to black. This is referred to as the additive color model.
- 20. The subtractive color model: Primaries – cyan, magenta and yellow. Also called the CMY model. Colors are generated by subtracting the three primaries from other colors.
- 21. The CIE Chromaticity: Represents colors in terms of three new primaries: x, Y and Z Basically an additive scheme.
- 22. Practical Colour Displays: When a transformation is necessary from the CIE standard colour chart to the colour produced on a specific display device, we must express the primary colours of the display device by x and y quantities. Good quality monitors will be calibrated for the CIE colour chart. For example, a colour CRT monitor may have the following primary colour sources: x y z Red 0.628 0.346 0.026 Green 0.268 0.588 0.144 Blue 0.150 0.07 0.780 These three points define a triangle on the CIE chromaticity diagram, as shown on diagram 10.5. Only the points inside this triangle may be reproduced by the display device
- 23. From RGB to XYZ: