Color and color models
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Color is a sensation produced by the human visual system. The two most common color models are RGB, used for computer displays, and CMYK, used for printing. RGB is an additive model that uses combinations of red, green, and blue light to produce colors. CMYK is a subtractive model that uses combinations of cyan, magenta, yellow, and black inks to produce colors. Both models represent colors using three numeric values corresponding to the intensities of the primary colors.
Color and color models
- 2. 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. Color is Human Sensation Cone and rod receptors in the retina Rod receptor is mostly for luminance perception 3 different types of cone receptors in the fovea of retina, responsible for color representation. Each type is sensitive to different wavelengths
- 4. Color model A color model is an orderly system for creating a whole range of colors from a small set of primary colors.
- 5. Types of Color model Subtractive Color Additive Color Additive color models use light to display color subtractive models use printing inks.
- 6. The Two Most Common Color Models RGB model For computer CMYK model For printing YCbCr model
- 7. RGB Color Model: Additive color model. For computer displays. Uses light to display color. Colors result from transmitted light. Red + Green + Blue = White.
- 8. The RGB Color Model If R,G, and B are represented with 8 bits (24-bit RGB image), the total number of colors is (28 )3=16,777,216
- 9. CMYK Color Model Subtractive color model. For printed material. Uses ink to display color. Colors result from reflected light. Cyan + Magenta + Yellow = Black Used internally in color printers Complementary to RGB: C=1-R M=1-G Y=1-B
- 10. Color Models the color model RGB is used in hardware applications like PC monitors, cameras and scanners, the CMY color model is used in color printers, Each color can be a point in the RGB color model cube. Red, green and blue are known as the primary colors. These colors can be added to produce secondary colors which are: magenta = red + blue cyan = green +blue yellow = red + green Other possible combinations: white = blue (primary) + yellow (secondary) white = green (primary) + magenta (secondary) white = red (primary) + cyan (secondary)
- 11. Additive vs. Subtractive Color Models Since additive color models display color as a result of light being transmitted (added) the total absence of light would be perceived as black. Subtractive color models display color as a result of light being absorbed (subtracted) by the printing inks. As more ink is added, less and less light is reflected. Where there is a total absence of ink the resulting light being reflected (from a white surface) would be perceived as white.
- 12. HSL and HSB Hue Hue is what most people think of when we say "color". Saturation Saturation is the "purity" of the color. It refers to the amount of gray paint mixed with the hue. Lightness Value refers to the intensity of light present.
- 13. HSL and HSB
- 14. Dithering Dithering is often used for displaying monochrome images creating the illusion of new colors and shades by varying the pattern of dots. Sometime call halftoning.
- 15. YCbCr YCbCr Color Space is used in MPEG video compression standards • Y is luminance • Cb is blue chromaticity • Cr is red chromaticity Y = 0.257*R + 0.504*G 0.098*B 16 Cr = 0.439*R 0.368*G 0.071*B 128 Cb = 0.148*R 0.291*G 0.439*B 128 YIQ color space (Matlab conversion function: rgb2ntsc):