1 / 10

COMPUTER GRAPHICS

COMPUTER GRAPHICS. CS 482 – FALL 2014. OCTOBER 22, 2014. COLOR. COLOR PERCEPTION CHROMATICITY COLOR MODELS. COLOR PERCEPTION. COLOR SENSITIVITY. The visible spectrum of light, illustrated at right, ranges from about 400 to 700 nanometers in the electromagnetic energy spectrum.

radwan
Download Presentation

COMPUTER GRAPHICS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. COMPUTER GRAPHICS CS 482 – FALL 2014 OCTOBER 22, 2014 COLOR • COLOR PERCEPTION • CHROMATICITY • COLOR MODELS

  2. COLOR PERCEPTION COLOR SENSITIVITY The visible spectrum of light, illustrated at right, ranges from about 400 to 700 nanometers in the electromagnetic energy spectrum. Empirical studies have indicated that the cones in the eye have different levels of sensitivity to different colors, indicating the eye’s response to pure blue light is much less strong than its response to pure red or green light. The RGB phosphors used in cathode ray tubes do not exactly produce “pure” shades of red, green, and blue, as indicated in the figure above, showing the eye’s response to the excited pixel colors. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 205

  3. COLOR PERCEPTION VISIBLE SPECTRUM Using an XYZ coordinate system (where the axes are “shades” of red, green, and blue, respectively, just outside the visible spectrum), the Commission Internationale de l’Eclairage(CIE – International Commission on Illumination) established a color standard that encloses the entire visible spectrum. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 206

  4. CHROMATICITY CIE CROMATICITY DIAGRAM Because of the differing sensitivities of the eye’s cones, visible color space is actually quite elaborate. An international standards organization, the CIE, developed three color-matching functions that could be combined to approximate the entire range of visible colors. When this space is sliced by the x+y+z=1 plane, the result is the CIE Chromaticity Diagram, pictured at right. Fully saturated colors lie around the diagram’s border, while unsaturated colors are in the center. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 207

  5. CHROMATICITY COLOR GAMUTS Triangular regions of the CIE Chromaticity Diagram, known as gamuts, are used to define the range of producible colors for a device. All colors within the gamut may be produced as linear combinations of the vertex colors. The US television standard, NTSC, uses Red: (0.6700, 0.3300), Green: (0.2100, 0.7100), and Blue: (0.1400, 0.0800). HDTV uses red: (0.6400, 0.3300), Green: (0.3000, 0.6000), and Blue: ((0.1500, 0.0600). Color CRTs use Red: (0.6280, 0.3460), Green: (0.2680, 0.5880), and Blue: (0.1500, 0.0700), as illustrated above. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 208

  6. CHROMATICITY COLOR BLINDNESS Deuteranopes Perceive Blues & magentas as violets. Perceive Greens & oranges as yellows. Perceive Cyans & reds as white. Tritanopes Perceive Oranges & magentas as reds. Perceive Greens & blues as cyans. Perceive Yellows & violets as white. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 209

  7. COLOR MODELS ADDITIVE AND SUBTRACTIVE SYSTEMS In digital display systems, each pixel in an image is represented as an additive combination of the three primary color components: red, green, and blue. Printers, however, use a subtractive color system, in which the complementary colors of red, green, and blue (cyan, magenta, and yellow) are applied in inks and toners in order to subtract colors from a viewer’s perception. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 210

  8. COLOR MODELS RGB CUBE A much simpler color model is the RGB cube, which merely sets a particular shade of red, green, and blue along the three coordinate axes, and linearly combines colors to obtain the colors inside the cube. While this approach is conceptually simple, it is quite inaccurate, since color perception is not, in fact, definable as a linear process. The hardware standard for color production is still a variation of CIE chromaticity; software and color printer standards tend to use a variation of the RGB cube. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 211

  9. COLOR MODELS HSV HEXCONE This color model takes a different approach, using hue (i.e., pure color, represented by the angle around the central axis to the cone), saturation (i.e., level of purity, represented by the radial distance from the axis), and value (i.e., brightness, represented by the distance up the central axis). • This model has the intuitive appeal of the artist’s tint, shade, and tone model: • pure red = H =0, S =1, V = 1; pure pigments are (i,1,1). • tints: adding white pigment is equivalent to decreasing S at constant V • shades: adding black pigment is equivalent to decreasing V at constant S • tones: “graying” by decreasing S and V A variation on this approach is the HSL (Hue-Saturation-Lightness) technique, which uses a double-hexcone approach instead of a single hexcone. CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 212

  10. COLOR MODELS POLAR COORDINATES Tilt cube and add seams HSV HEXCONE Example vertical cross-sections Force RGBCMY into a plane Expand horizontal slices Round off hexagonal exterior RGB CUBE HSL DOUBLE HEXCONE CS 482 – FALL 2014 OCTOBER 22, 2014: COLOR PAGE 213

More Related