Visual Imaging and the Electronic Age Color Science

Transcription

1 Visual Imaging and the Electronic Age Color Science Color Gamuts & Color Spaces for User Interaction Lecture #7 September 16, 2014 Donald P. Greenberg

2 Color Triangle for XYZ Y g 2 1 Z r -2-1 b 1 X

3 XYZ Assumptions 1. One coordinate, and one coordinate only, should represent the luminance. 2. The line between x and y should be nearly coincident with the spectral locus for colors in the 550nm to 700nm (greenred) range. 3. The spectral locus of all realizable colors should lie in the allpositive XYZ quadrant. For realizable colors, all XYZ values and all color matching functions are positive.

4 XYZ Color Matching Functions All positive values y is the luminous efficiency function Equal area

5 XYZ Color Space

6 Describing Color in XYZ Luminance Y Chromaticity x y z X X Y Y X Y Z X Y Z Z Z x y z 1

7 Chromaticity Diagram

8 Chromaticity Diagram

9 Chromaticity Diagram

10 The luminance or lightness axis, when added to the chromaticity diagrams provides the third dimension for color.

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13 3D Model - Billmeyer

14 Color Demonstration Video (Jeremy Selan Color Cube Demo)

15 Trichromatic Generalization Many colors can be matched by additive mixtures of suitable amounts of three fixed primary colors. Others have to be mixed with a suitable amount of one before it can be matched by the other two. All the colors can be matched in one of these two ways: The restriction is that none of the primary colors can be matched by an additive mixture of the other two.

16 Color Gamuts

17 Trichromatic Generalization Many colors can be matched by additive mixtures of suitable amounts of three fixed primary colors. Others have to be mixed with a suitable amount of one before it can be matched by the other two. All the colors can be matched in one of these two ways: The restriction is that none of the primary colors can be matched by an additive mixture of the other two.

18 Commentary When we describe Grassman s Experiments, we derived response matching functions which had negative values. How can we have negative light? This is not physically possible. Reproduction is limited to the domain within the triangle defined by the three phosphor/inks.

19 Chromaticity Diagram & Gamut (monitors)

20 Chromaticity Diagram & Gamut (monitors) Dominant Hue

21 Chromaticity Diagram & Gamut (monitors).. Nearest Color

22 Chromaticity Diagram & Gamut (printers)

23 Sharp 4 Color Display

24 Sharp 5 Color Display

25 5 Color Gamut Color coordinates and gamut for five-primary LCDs. Hui-Chuan Cheng, Linghui Rao, Shin-Tson Wu. Color Breakup Suppression in Field-Sequential Five-Primary-Color LCDs, Jourrnal of Display Technology, June 2010.

26 Expanded colar gamut reproduced by sixprimary projection display

27 Expanded color gamut reproduced by sixprimary projection display

28 Color Space Diagram with Various Gamuts

29 Color Spaces for User Interaction RGB Cube Hexacone Model Munsell Color System HSL Biconical Solid (Hue, Saturation, Lightness) Others

30 RGB Cube B Blue Cyan Magenta White Black Green G R Red Yellow

31 Hexacone Model

32 Hexacone Model Alvy R. Smith

33 Perceptually Uniform Color Spaces Chromaticity specifies the basic color (hue) of an object. Comparing chromaticities gives the best indicator of the color differences between two objects. A chromaticity diagram where equal physical distances (on the diagram) indicate equal perceptual differences would be useful. Why?

34 MacAdam Experiments Subjects were shown colors of known chromaticity (luminance was held constant) and were asked to match the sample using an adjustable color source. Each chromaticity point studied is surrounded by an ellipse proportional in size to the standard deviation of the difference between the actual and match chromaticities. The ellipse indicate how rapidly the color change is perceived.

35 Just Noticeable Differences (JND s) MacAdam Ellipses Note the varying size and orientation of the ellipses. Donald P. Greenberg - Cornell Program of Computer Graphics

36 MacAdam Ellipses - Nonlinear Color Spaces (uvw) u 6y 2x x 1.5 v 6y 3y x 1.5 Basis for the CIELUV and CIELab systems

37 Munsell Color System Billmeyer

38 Munsell Color System Meyer

39 Munsell Color System Meyer

40 Biconical Color Solid George Joblove

41 Biconical Color Solid George Joblove

42 Biconical Color Solid George Joblove

43 End...

44 Converting RGB primaries to XYZ λ R = 650nm λ G = 530nm λ B =460nm X Y = Z R G = B R G B X Y Z

45 Converting RGB primaries to XYZ λ R = 700nm λ G = 546nm λ B =435nm X Y = Z R G = B R G B X Y Z

46 Converting YIQ to XYZ X Y Z = Y I Q Y I Q = X Y Z