Color model in computer graphics
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This document discusses color models, including RGB and HSV color models. It provides the following key points: 1. A color model is a system that represents a range of colors using a small set of primary colors. The RGB and HSV models are commonly used. 2. The RGB model uses additive color and is used for computer displays. It represents color using levels of red, green, and blue. 3. The HSV model represents color in terms of hue, saturation, and value (brightness). Hue specifies the color, saturation specifies the purity of the color, and value specifies the brightness.
![Conversion RGB to HSV
• Input: RGB
• Output: HSV
• Step1: [normalize the RGB values to be in the range [0, 1]]
• r = R/ 255
• g = G/ 255
• b = B/ 255
• Step2: [Find the difference between max and min values]
• M = max(r, g, b), m = min(r, g, b).
• And, difference Δ = M-m.
• Step3: [Calculate value V]
• V = max(r, g, b)
• Step4: [Calculate saturation S]
• If Δ = 0, then S = 0, otherwise S = Δ / M
• Step5: [Calculate hue H]
• If M=r then H = 60*((g-b / Δ) * mod 6)
• If M=g then H = 60*(2 + (b-r)/Δ)
• If M=b then H = 60(4 + (r-g)/ Δ)
• Step6: [output HSV]
• The calculated H, S, and V are the output of the algorithm.
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Color model in computer graphics
- 2. References • R.C. Gonzales and R.E. Woods, Digital Image Processing, Addison-Wesley, Reading, 1992. • I. Newton, Opticks, 4th Edition, Dover, New York, 1704/1952. • Internet • Nipun Thapa’s Notes. 2
- 3. What is Color ? • Color is a sensation produced by the human eye and nervous system. • It is useful to represent a color by a set of exactly three numbers. 3
- 4. Color Model • A color model is an orderly system for creating a whole range of colors from a small set of primary colors. • It is an abstract mathematical model describing the way colors can be represented as tuples of numbers. 4
- 5. Most Common Used Color Model • RGB Model • HSV Model 5
- 6. RGB Color Model: Additive color model. For computer displays. Uses light to display color. Colors result from transmitted light. Red + Green + Blue = White. 6
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- 8. HSV Color Model • Hue, Saturation, Value(Brightness) • Hexcone subset of cylindrical (polar) coordinate system. 8
- 9. Means……. • Hue - The color we see (red, green, purple). • Saturation - How far is the color from gray (pink is less saturated than red, sky blue is less saturated than royal blue). • Brightness/Lightness (Luminance) - How bright is the color. 9
- 10. Hue • Hue (H), the color type (such as red, green). • It ranges from 0 to 360 degree, with red at 0 degree, green at 120 degree, blue at 240 degree and so on. 10
- 11. Saturation • Saturation (S) of the color ranges from 0 to 100%. Also sometimes, it called the "purity". • The lower the saturation of a color, the more "grayness" is present and the more faded the color will appear. • Saturation Scale 11
- 12. Value • Value (V), the Brightness (V) of the color ranges from 0 to 100%. • Value Scale 12
- 13. HSV & RGB Color Picker The HSV color picker is used to control the V value, while the corresponding slices through the cylinder are displayed, and a color is selected by clicking on a point in the disk. The RGB picker below simply uses sliders to control the three components, while the spectrum picker at the bottom lets you pick your color directly by clicking. 13
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- 15. Conversion RGB to HSV • Input: RGB • Output: HSV • Step1: [normalize the RGB values to be in the range [0, 1]] • r = R/ 255 • g = G/ 255 • b = B/ 255 • Step2: [Find the difference between max and min values] • M = max(r, g, b), m = min(r, g, b). • And, difference Δ = M-m. • Step3: [Calculate value V] • V = max(r, g, b) • Step4: [Calculate saturation S] • If Δ = 0, then S = 0, otherwise S = Δ / M • Step5: [Calculate hue H] • If M=r then H = 60*((g-b / Δ) * mod 6) • If M=g then H = 60*(2 + (b-r)/Δ) • If M=b then H = 60(4 + (r-g)/ Δ) • Step6: [output HSV] • The calculated H, S, and V are the output of the algorithm. 15
- 16. Conversion HSV to RGB • Input: HSV • Output: RGB • When 0 ≤ H < 360, 0 ≤ S ≤ 1 and 0 ≤ V ≤ 1. • C = V × S • X = C × (1 - |(H / 60º) mod 2 - 1|) • m = V – C • (R, G, B) = (R'+ m, G'+ m, B'+ m). 16
- 17. Application of Color Model • RGB model is used in hardware devices such as computer monitors, cameras, and scanners. • HSV color model is used in real life applications to describe perception of viewer. 17