Grafisk Teknik. Grafisk Teknik. Grafisk Teknik. Reiner Lenz. Reiner Lenz. Reiner Lenz

Transcription

1 Grafisk Teknik Reiner Lenz Grafisk Teknik Reiner Lenz Grafisk Teknik Reiner Lenz 1

2 Content and Goals Basic color perception and color vision facts Mathematical modeling of color science/color image processing problems Basic understanding of CIE colorimetry Color Management Systems BEFORE: Matlab, Linear Algebra GRAFISK TEKNIK, TNM011 AFTER: TMN012, More Matlab, More Linear Algebra, TNM025: Image Database Search Part 0: Literature Sharma: Digital Color Imaging Handbook Sharma: Available at bibl.liu.se Selected pages from Chapter 1 2

3 Westland, Ripamonti: Computational Colour Science using Matlab Available as e-book: under bibl.liu.se + netlibrary G.Wyszecki, W.S. Stiles: Color Science The Color Bible M.D. Fairchild: Color Appearance Models Describes how we perceive color. Additional text. 3

4 S. Zeki: Inner Vision Art/Brain/Color/Perception. Additional text. Additional (older) Literature E.J. Giorgianni and T.E. Madden: Digital Color Management Addison- Wesley, P.K. Kaiser and R.M. Boynton: Human Color Vision, OSA, L.W. MacDonald:Using color effectively in computer graphics. IEEE Computer Graphics and Applications July/August M.A. Webster:Human colour perception and its adaptation. Network, J. Hardeberg: Acquisition and Reproduction of Color Images: Colorimetric and Multispectral Approaches, 2001 ($10 Part 1: Color Everywhere Color is important Color is difficult Color is useful 4

5 Everybody knows what color is Search for color on the web: a visual attribute of things that results from the light they emit or transmit or reflect; "a white color is made up of many different wavelengths of interest and variety and intensity; "the Puritan Period was lacking in color" the timbre of a musical sound; "the recording fails to capture the true color of the original music" a race with skin pigmentation different from the white race (especially Blacks) an outward or token appearance or form that is deliberately misleading; "he hoped his claims would have a semblance of authenticity"; "he tried to any material used for its color; "she used a different color for the trim" (physics) the characteristic of quarks that determines their role in the strong interaction; each flavor of quarks comes in three colors the appearance of objects (or light sources) described in terms of a person's perception of their hue and lightness (or brightness) and saturation add color to; "The child colored the drawings"; "Fall colored the trees"; "colorize black and white film" affect as in thought or feeling; "My personal feelings color my judgment in this case"; "The sadness tinged his life" modify or bias; "His political ideas color his lectures" decorate with colors; "color the walls with paint in warm tones" gloss or excuse; "color a lie" change color, often in an undesired manner; "The shirts discolored" having or capable of producing colors; "color film"; "he rented a color television"; "marvelous color illustrations" A property of quarks that expresses their behavior in the presence of the strong nuclear force; analogous to electrical charge, but there are thre broad band intensity of the spectrum through filters; if an object is equally bright as seen through different filters, the asteroid is referred t between the brightness through two filters LEDs are designed to give off a specific color emission. The dominant wavelength is a quantitative measure of an LED color as perceived by the hum range required for your application. Some applications may have color constraints in order to meet specific government specifications or regulatory gu For human beings: our perception of radiant visible energy seen as hue, intensity, value and temperature reflected from a surface, or transmitted The measurement of white paper based on the color scale (L, a, b). "L" represents the lightness on a scale of 0 for black and 100 for perfect white, " 1) Used to refer to perceived qualities that result from the response of vision to the wavelength of reflected or transmitted light. 2) Describes Light waves that reach the viewer's eye by transmission (through an object between the viewer and the light source) or by reflection (when light w apple looks red because it absorbs all colors in white light except red, which it reflects. White objects reflect all and black objects absorb all lig consists of the characteristics of light other than spatial and temporal inhomogeneities; light being that aspect of radiant energy of which a hum Color in water can be caused by the presence of such things as plankton, decaying organic matter, industrial wastes, and sewage. "True color" - th usually measured by comparing the color of a water sample to that of a fixed standard. Color is expressed in terms of "color units" where one color un (1) a visual sensation produced in the brain when the eye views various wavelengths of light; (2) the appearance of objects or light sources descr sources. The phenomenon of color results from the interaction between a light source, an object and an observer. Standard mathematical models can be used t data, and observers are quantified by the observer functions. These three elements can then be combined to calculate values that correspond to how the Measured in color units that relate to a standard. A yellow-brown natural color is associated with lakes or rivers receiving wetland drainage. The and therefore the depth at which plants can grow. Refers not to the actual color of things, but to the fact that there are two distinct kinds of each, and these are given the names `black', and `w The particular color of a tape' when looking at the backing' regardless of the color of the adhesive. What a precision shooter hollers if the dealers give them any heat over setting the dice. In doing so, he announces his intention to leave the tab denominations prior to his departure. The shooter will remain at the table to await the outcome of any contract wagers (non removable). If the shooter The color scale is used to describe the color tones of a gemstone. For diamonds, the color scale ranges from D, meaning completely colorless, to Z the color is measured by tone and hue. See also Tone and Hue. Response of the eye to different wavelengths of light. Ultraviolet < 400 nm, violet nm, blue nm, green nm, yellow Some History of Color Science Some Color Science History Greece (400BC) : Four basic elements: earth, air, fire and water Inner fire sends out rays, they interact with outer rays emerging from the objects. Tiny copies of the objects are transferred back and compared in the mind Arab culture (Abu Ali Mohammed Ibn Al Hazen ( A.D.): Assumed that: human eye is similar to a pinhole camera color of an object depends on the color of the light and the properties of the object Leonardo da Vinci ( ) : Perspective drawing and similarity to the pinhole camera Kepler ( ) : Effects of lenses Newton ( ) : Experiments with prisms White is a combination of colored lights Color of an object is related to the ability to reflect the colored rays Trichromacy: J. C. Le Blon described how to print with the help of three colors in 1723 M. Lomonosov described mixture of three primary colors and trichromatic perception in 1757 Thomas Young described trichromacy in its modern form in 1802 Helmholtz ( ) popularizes trichromacy 5

6 Objective vs. Subjective Color Theories Newton vs. Goethe: Newton showed that white light can be understood as a combination of light of different wavelengths Goethe claimed that complex processes can only be understood holistically Helmholtz vs. Hering: human Helmholtz showed that trichromacy is the basis of color perception since the visual system is based on three sensors Hering used psychological experiments that showed that black/white red/green yellow/blue are opposed to each other. So he postulated that the visual system is based on three opponent color channels. Color is multi-disciplinary Medicin (eye, brain, ) Biology (animal vision) Art Technology Mathematics Physics Psychology Economy Color Matters - Some Observations Printing: Was an art requiring long experience. This knowledge is rapidly disappearing. Printing today is to a large extend a digital technique Computational techniques are required Networking: Databases/Printing/Content/Construction Digital Cameras replace analogue cameras Computational photography: Camera+computer=1 System Computer Graphics and Visualization: Realistic color is important 6

7 New Technologies Everybody can create and print documents Digital Cameras/Ink Jet Printers/Monitors Multimedia Computers Digital Cinema/Camera Telephone Computational photography All of them need tools to describe and process color information Graphics/Movies/Cosmetics/Medicin Realistic Skin Modelling (Tsumura, Chiba U, Japan) Networking Cad Design Production Marketing Sales Germany Italy China Sweden Everywhere Correct Properties Interaction with surroundings Quality control Reproduction on monitor Reproduction in catalogue Reproduction in newspaper Print Quality Control on different paper Exact description and communication of color is essential 7

8 Photography Analog Digital Chemical Signal Canon Digital Camera Software Color is important in Search Engines Scene=objects+illuminations Analog camera Digital camera Signal processing Image understanding Example: Image retrieval 8

9 Digital Cameras What s next? Computer Aug Computational Photography-The Next Big Step Computational Cameras: Redefining the Image Light Fields and Computational Imaging The Moment Camera Virtual Cinematography: Relighting through Computation Multispectral Systems Aixperts-Aachen Germany Multispectral Scanner and Display for Industrial Applications Crisatel Scanner of paintings Sony Camera with internal 4 channel sensor Chiba University Japan three-dimensional, five-channel camera Part 2: Human Color Vision 9

10 Physics-Psychophysics COLOR IS INSIDE THE BRAIN! Some illustrations that color is more than physics Simultaneous Contrast Color needs contours Hans Irtel 10

11 Simultaneous Contrast Hans Irtel Color Spectra Color originates in light Light is electromagnetic radiation It can be described by wavelength Humans can see light of wavelengths in the range 380nm to 800nm Electromagnetic Radiation Wikipedia 11

12 Functions of wavelength Spectrum S(λ) = Number of photons of wavelength λ The Human Eye - Hardware Human eye 12

13 Human Eye: Receptors Two type of sensors: Rods responsible for low-intensity situations (only intensity, black-white, detection) Cones active in normal light conditions (three types enabling to trichromaticcolor vision) The retina Flow of Light Psychophysics:Weber Fechner Law Given an intensity I and perceived brightness R R is the smallest increment such difference between R and R+ R can be seen Then leads to or differential equation which means that R must be an exponential function R(I) = c 1 exp(c 2 I) 13

14 Human color vision Spectral sensitivity curves are Probability Curves: Photon of a given wavelength hits cone -> an impulse is generated with a given probability After the impulse is generate it is not possible to recover the wavelength of the photon Relative sensitivity of the eye Human color vision is most sensitive to medium range wavelength around 555nm Known as V(λ) Characteristics of human color vision Human cones are sensitive for short (S-cones) medium (M-cones) and long (L-cones) wavelengths Number of L-M-S cones = 40:20:1 No S-cones in the centre of the retina! 14

15 Spectral sensitivity of human pigments Human/Animal Color Vision Most animal vision is intensity based (no color) First a second type of cones were added, the S-cones This is the ancient system Then (30 million years ago) middle range cones modify into M- and L-cones This is the modern system Color Blindness 15

16 Color Blindness roughly 1 in 10 men are fully or partly colour blind. one of the three types of colour detectors is either faulty or missing Strawberries. Strawberries as they would appear to someone who is red/green colorblind. Types of color blindness Protanope: 1% male, 0.02% female nm, blue nm yellow L pigment missing Deuteranopia: 1% male, 0.01% female nm blue nm yellow M pigment missing Tritanopia: 0.002% male, female nm blue, nm red Probably S pigment missing Types of color blindness II 16

17 Example 1 Example 2 Illustration of color deficiency Interactive demonstration of colour appearance for the 'colour-b Vischeck simulates colorblind vision 17

18 Further comments Differentiation between M- and L-cones may result from discrimination for certain fruits There may be more than 3 color receptors Young-Maxwell- Helmholtz/Hering Young-Maxwell-Helmholtz described color vision in terms of three channels, based on the three receptor types red-green-blue (trichromatic model) Hering developed oppenent color pairs: red-green, blue-yellow, black-white There is no greenish-red but reddish-yellow (opponent color model) Trichromatic and opponent color models are combined in newer models of color vision 18