Computer Vision Pattern Recognition Lab Computer Graphics Chapter

Computer Vision & Pattern Recognition Lab. Computer Graphics Chapter 19 Color Models and Color Applications Computer Vision & Pattern Recognition Lab.

19. 1. Properties of Light n Light: electro magnetic wave (전자파) 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 2

19. 1. Properties of Light n Depending on the wavelength of the wave, Short wavelength (380 -450 nm, 6. 7 -7. 9 x 1014 Hz): violet n Long wavelength (620 -750 nm, 4. 0 -4. 8 x 1014 Hz): red n Lights with all frequency in visible range: white n 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 3

19. 1. Properties of Light Perception(Qualitative) Hue : 색상 Saturation : 채도 Value(Brightness) : 명도 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 4

19. 1. Properties of Light Perception(Qualitative) Colorimetry(Quantitative) Hue : 색상 Dominant wavelength Saturation : 채도 Purity (Bandwidth) Value(Brightness) : 명도 Luminance(Amount of energy) 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 5

19. 2. Color Models For most purposes, three primary colors can be combined to produce almost all visible colors: tri-stimulus theory n No finite set of real primary colors can produce all possible colors. n Color gamut: set of all colors that can be produced from the primary colors n 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 6

19. 3. XYZ Color Model The CIE (Commission Internationale d’Eclairage) defined three hypothetical lights X, Y, and Z n Idea: any wavelength can be matched perceptually by positive combinations of X, Y, and Z n x≈R y≈G z≈B 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 7

19. 4. RGB Color Model Based on tri-stimulus theory of vision n Our eyes perceive color through the stimulation of 3 (R, G, B) visual pigments in the cones of the retina n 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 8

19. 4. RGB Color Model 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 9 / 35

19. 4. RGB Color Model 2020 -11 -24 Computer Vision & Pattern Recognition Lab. Original R G B 10

19. 5. YCr. Cb/YUV/YIQ Color Model n YCr. Cb Used for MPEG/JPEG n Y: Luminance n Cr, Cb: Chrominance (color info. ) n n YUV PAL encoding for Color TV n Y: Luminance n U, V: Chrominance (color info. ) n n Y = 0. 3 R + 0. 59 G + 0. 11 B Cr = (R-Y) Cb = (B-Y) Y = 0. 3 R + 0. 59 G + 0. 11 B U = (B-Y)× 0. 493 V = (R-Y)× 0. 877 YIQ NTSC encoding for Color TV n Y: Luminance n I, Q: Chrominance (color info. ) n 2020 -11 -24 Y = 0. 30 R + 0. 59 G + 0. 11 B I = 0. 60 R - 0. 28 G 0. 32 B Q = 0. 21 R - 0. 52 G + 0. 31 B Computer Vision & Pattern Recognition Lab. 11

19. 5. YCr. Cb/YUV/YIQ Color Model 2020 -11 -24 Original Y U V Computer Vision & Pattern Recognition Lab. 12

19. 6. CMY Color Model n CMY Subtractive color model n Cyan, Magenta, Yellow n Complements of RGB n Used for printers n 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 13

19. 7. HSV Color Model n HSV (HSB) Model Based on human perception n Hue, Saturation, Value n Cylindrical coordinate n 2020 -11 -24 Computer Vision & Pattern Recognition Lab. 14

n Color conversion 16 / 30