1 / 27

Sensory Information Processing

Sensory Information Processing. Color space Perception and reproduction of color. Light and Color. Light : physical Light is a electromagnetic wave Physically, there is no concept of “color” (distribution with respect to the wavelength ) color ： psychological

galena-barlow
Download Presentation

Sensory Information Processing

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. Sensory InformationProcessing Color space Perception and reproduction of color

  2. Light and Color • Light : physical • Light is a electromagnetic wave • Physically, there is no concept of “color”(distribution with respect to the wavelength) • color：psychological • One aspect of perception of the light • Relative intensity of three ranges of wavelength  To learn about color, we must learn about human

  3. eyeball • diameter 24mm • Flexible lens (crystalline) • Iris = aperture • Focal length = 17mm • Retina : film or CCD Fovea

  4. Fovea • Center of the image • Highest resolution

  5. Retina • Two types of photo receptor • Rod : monochromatic, high response, work in dark environment • Cone : three types (L, M, S) : colorlow response, work only at bright environment

  6. Spectral sensitivity of cones measured neurophysiology

  7. How to identify the color perception? How to measure the relationships between wavelength and color perception • Measuring signals of neurons • Not easy • Perception is not directly related to signal • Subjective tests • Comparing very single spectral light with additive color mixture • Ambiguity of coordinate transform remains

  8. Negative response Color matching experiment(1) • Adjust the levels of R, G, B so as to match to monochromatic light • R : 700nmG : 546.1nmB : 435.8nm

  9. Color matching(2) • Negative value means the light at opposite side All in positive ith negative values

  10. Why we have “negative values”? • No negative response at our retina Actual spectral response(unknown) sensitivity M(λ) S(λ) S=∫S(λ)・i(λ)dλ L(λ) wavelength × Sample stimulus L intensity i(λ) λ change M wavelength Smooth curve in positive region

  11. B R G Why we have “negative values”? S i=B • R>0, G=B=0 when i = 700nm(R) • RGB space is smaller than the original space with our actual sensitivity. Therefore, between the wavelength of B and G, R should be negative i=G L i=R i λ M

  12. S B B r g L R R G M G rg chromaticity coordinate i=B • rg : chromaticity : Relative values of RGB r = R/(R+G+B), g = G/(R+G+B) Single wavelength passes three points(r,g)=(0,0), (0,1), (1,0) Linear trransform i=G i=R λ

  13. rg chromaticity and RGB color matching curve • All three values have negative regions

  14. XYZ color space • To avoid the negative values of RGB color space New coordinate system which includes the spectral curve in positive areaThree points, X, Y, Z, is outside of spectral curve, so, it does not physically exist called as”imaginary color”

  15. XYZ color matching function CIE1931 XYZ color matching function

  16. xy chromaticity • Relative value of XYZ • x = X/(X+Y+Z),y = Y/(X+Y+Z) • Black curve : black body radiation (related to the color temperature)

  17. White light source xy chromaticity and brightness • Reflectance is limited to 1.0 or below • White is brightest • Intensity of the boundary of spectral curve is 0 • Called MacAdam limit intensity Object with various color

  18. Color reproduction and gamut(1) • Range of additive color is limited in the triangle which verteces are primal colors • Called gamut • left figure indicates the range of RGB tristimulus

  19. Display and color reproduction • Range of the color depends on the primal colors • “RGB” of PC is not CIE RGB • Wrong use of color space causes the color mismatch s

  20. examples • Color space of digital camera • Adobe Photoshop • Apple ColorSync • Display

  21. Printing and color • Printing is subtractive color (CMY) • Inside the convex hull which defined by 6 points of C, M, Y, CM,CY, MY • RGB and CMY have different gamut

  22. print cyan green black blue magenta red yerrow white • Convex hull of 6 primal colors yellow=R+G yellow=R+G magenta=R+B cyan=G+B White material (paper) ・spectral reflectance of green ≒ yellow ・ cyan →spectral reflectance of green is linearly independentfrom yellow and cyan ・represented by halftone dot →mixture of 8 colors above Halftone dot

  23. Color space matched for perception • HSB color space • Polar coordinate • HSB (Hue, Saturation, Brightness) • xy color space • Perceptually not uniform • MacAdam ellipse

  24. L*a*b* color space • Perceptually uniform color space by nonlinear transform

  25. Metamerism • Visually same color but different spectral curve • Depends on not only the object but also the light source × Perception R Object 1 Light 1 same `erception R Perception G same `erception G Perception B same × Light 2 Object 2 Perception B

  26. Spectral sensitivity and evaluation of color • If the spectral sensitivity of the sensor is different from the human beings, color matching fails • If the spectral curve of light source is special, color matching fails (object with different colors seems same) • （fluorescent light is not good as light bulb)

  27. Psychology vs. Physics • Psychology • System which works as same as human • Color quality control • physical • Color marker (distinguish objects with color) • Recognition of material using color • Marginal • QC of papers using color (visual, or other?) • QC of agricultural products

More Related