Propelled PC Design: Shading.


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To depict the human visual framework and our impression of shading ... do we guarantee that the distinctive representations make the same visual impact? ...
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Advanced Computer Graphics: Color James Gain Department of Computer Science University of Cape Town jgain@cs.uct.ac.za Advanced Computer GraphicsCollaborative Visual Computing Laboratory

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Objectives To depict the human visual framework and our view of shading To acquaint the material science of shading With spread a scope of shading models and their relative benefits Advanced Computer Graphics

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What is Color? physical depiction: a spectra of wavelengths. mental recognition: a jolt sent from the optic framework to the mind. PC depiction: distinctive arrangements of bases and facilitates, contingent upon the sort of showcase and application. Issue: How would we guarantee that the distinctive representations make the same visual impact? Propelled Computer Graphics

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Sight Arguably our rule methodology. A zone of significant innovative work. Parts: Wetware: The human visual framework. Equipment: Visual showcase frameworks (e.g. PC screen). Programming: Rendering of 3D scenes (e.g. PSC). Perceptual Terms: Hue: Distinguishes among hues, for example, red, green, purple and yellow. Immersion: Refers to how far a shading is from a dim of equivalent power. (How serious is the tint) Brightness: the apparent power of a self-luminating object. (The amount of light is discharged). On the other hand, gentility alludes to force from a reflecting item. Propelled Computer Graphics

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Human Visual System The lens of the eye shapes an altered picture of the world on the back surface (retina) of the eye. Cones: 150000 for every square millimeter in the fovea. High determination, shading. Poles: Lower determination monochromatic. Fringe vision: so we keep the high-res district in setting and abstain from being hit by passing branches. Data is gone to the visual cortex (which performs amazingly complex preparing). Propelled Computer Graphics

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Visual Cortex: Tristimulus Reality? Sorts of Cones: Low: 560 nm red ? Medium: 530 nm green ? High: 420 nm blue ? Sign to cerebrum: L - M ® red - green H - (L+M) ® blue - yellow L + M ® red + green » general luminance Red/Green visual impairment implies no sign L – M signal. Propelled Computer Graphics

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Hardware: The Ultimate Display Ivan Sutherland\'s "Definitive Display" [1965] hypothesized a showcase which created pictures vague from reality. Prerequisites of extreme Head Mounted Display (HMD): Viewing separation: 10cm Human visual sharpness: 1\' ( ) of visual circular segment on average 5" ( ) in the best-case Field of View (FOV): Horizontal = 200 deg Vertical = 100 deg Update Rate: 60Hz Must likewise coordinate different parts of Human Visual System. Required Flat Screen Resolution: 1\' visual keenness requires 12000x6000 pixels 5" visual sharpness requires 144000x72000 pixels Advanced Computer Graphics

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Saturation Tints Tones Brightness Grays Shades Artists\' Perception of Color Artists blend white and dark with unadulterated hues Tint = Pure shading + white Shade = Pure shading + dark Tone = Pure shading + dark + White Pure Color Black Advanced Computer Graphics

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Physics of Color: Colorimetry Light is electromagnetic vitality in the 400-760nm wavelength Perceived as a range of hues: violet, indigo, blue, green, yellow, orange, red. Light vitality, exhibit all the while at every wavelength, is spoken to as an otherworldly vitality circulation, P( l ) . Material science versus Discernment: Hue = prevailing wavelength Saturation = excitation virtue Brightness (self-radiant articles), daintiness (reflecting items) = luminance (measure of light) Pure shading: a solitary profoundly overwhelming wavelength Advanced Computer Graphics

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Spectral Distribution One shading = one ghostly vitality appropriation Energy P( l ) Wavelength l 400 nm Violet 760 nm Red Advanced Computer Graphics

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Hue, Saturation and Brightness Energy P( l ) Dominant wavelength e2 Brightness = territory under the bend Saturation e1 l 400 nm Violet 760 nm Red Hue Advanced Computer Graphics

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Retina Response Fraction of light consumed by the three sorts of cones (R, G, B): 0.2 G R Light Absorbed B l 0.0 760 nm Red 400 nm Violet Advanced Computer Graphics

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Retina Luminous Efficiency The eye\'s reaction to light of consistent luminence with fluctuating predominant wavelength. Top affectability (capacity to determine point of interest) is to yellow-green light. 100 Relative Sensitivity l 0 760 nm Red 400 nm Violet Yellow-Green 550 nm Advanced Computer Graphics

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Color Definition Define a shading by its phantom circulation: Large memory prerequisites to make a sufficient examining of the dispersion. Prevailing wavelength (tone) is not generally quickly self-evident. Metamers: Different spectra with the same shading reaction. No uniqueness. Requirement for more straightforward bases: depicting all hues with a one of a kind arrangement of directions Advanced Computer Graphics

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Metamers Same orange-like shading Energy P( l ) l 400 nm Violet 760 nm Red Advanced Computer Graphics

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Primary Colors Since our cones are delicate to red, green and blue why not portray all hues as a straight blend of these primaries? Beneath: estimation of three primaries required to match all wavelengths. Values V( l ) l 400 nm Violet 760 nm Red Advanced Computer Graphics

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CIÉ Model Commission Internationale de l\'éclairage characterized a shading model in 1931. Three standard essential capacities: X, Y, Z Defines all obvious hues Only positive coefficients Y = retina luminance recognition capacity X and Y = chromaticity Advanced Computer Graphics

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CIÉ Basis Functions Values V( l ) Z Y X l 400 nm Violet 760 nm Red Advanced Computer Graphics

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CIÉ Chromaticity Diagram Project the CIÉ plane of steady iridescence (X+Y+Z=1) onto the X-Y plane. Propelled Computer Graphics

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CIÉ Chromaticity Diagram Colors on the horseshoe edge are completely soaked. Integral hues are those that can be blended to create white light. Graph components out luminence so cocoa (orange-red at low level luminance with respect to its encompassing region) does not show up. Prevailing wavelength can be computed by drawing a line from white through the shading and crossing the edge. Nonspectral hues (purple and red) crossing the base of the horseshoe don\'t have a prevailing wavelength. Propelled Computer Graphics

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CIÉ Chromaticity Perimeter y Green 520 540 560 Yellow 500 580 White 600 Cyan Red 480 700 Purple x 400 Advanced Computer Graphics

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CIÉ Chromaticity Attributes y Green B Yellow A D Cyan Red C E F G Purple x Advanced Computer Graphics

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Mixing Colors y Green All hues on a straight line section can be made by blending the endpoints. So also, hues inside a triangle are a blend of the endpoints. Yellow I Cyan Red J K Purple x Advanced Computer Graphics

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CIÉ Color Gamuts Monitor RGB Gamut Film Gamut x Advanced Computer Graphics

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Beyond CIÉ 1931 Equal strides over the Chromaticity Diagram don\'t compare to measure up to perceptual separations. CIÉ 1976: perceptually uniform LUV: L for softness U and V for chromaticity Advanced Computer Graphics

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Computer portrayal Display gadget based shading spaces: RGB (screen) CMYK (printer) YIQ (TV) Perception based shading spaces: HSV (client cooperation) Need to: Correct for various presentation qualities Convert between shading models Advanced Computer Graphics

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RGB Color Model Red, Green and Blue primaries. Most understood shading space. Utilized (inside) in each screen. Added substance (hues added to a dark foundation) Black = (0,0,0), White = (1,1,1) Advanced Computer Graphics

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CMY Color Model Cyan, Magenta and Yellow Primaries Used (inside) in shading printers Substractive (hues subtracted from a white foundation) Black = (1,1,1), White = (0,0,0) Complementary to RGB: Advanced Computer Graphics

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The RGB/CMY 3D square Blue Cyan Magenta White Black Green Red Yellow Advanced Computer Graphics

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CMYK Color Model CMYK (Cyan, Magenta, Yellow, blacK) Mostly for printer use Saves on hued inks by utilizing dark ink beyond what many would consider possible therefore dull hues dry all the more rapidly Converting from CMY to CMYK Black is utilized rather than equivalent measures of C, M, Y. K = min(C,M,Y) C = C – K M = M – K Y = Y – K Advanced Computer Graphics

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YIQ, YUV Color Model U.S. business TV Recoding of RGB for: Transmission effectiveness Backward similarity with Black and White TV (drop I and Q) YIQ = NTSC Y is luminance I and Q are chromaticity YUV=PAL Exploits visual framework: More delicate to changes in luminance (Y) than chromaticity (I and Q) - > more transfer speed for Y Objects covering a little field of perspective produce constrained shading sensation - > it is possible that I or Q can have lower data transfer capacity. Proportion Y:I:Q = 4:1.5:0.6 Advanced Computer Graphics

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HSV Color Model Hue, Saturation and Value Primaries Cylindrical co-ordinate framework: Hue (H = 0 – 360 deg) revolution Saturation (S = 0.0 – 1.0) range Value (V = 0.0 – 1.0) stature User arranged and in light of the instinctive advance of craftsman\'s hues (tone, tint, shade). Spoken to by a hexcone. Propelled Computer Graphics

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The HSV cone Green Yellow Cyan Red White Blue Magenta Black Advanced Computer Graphics

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HSV transformation Flatten RGB 3D shape along the askew to make HSV hexagon There is a calculation for changing over in both headings RGB to HSV: max = max(r,g,b); min = min(r,g,b)[ V = max S = (max-min)/max H = more convoluted Green Yellow Red Cyan Blue Magenta Advanced Computer Graphics

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HSV properties Interpolating Color: Linear addition of the same two hues in RGB, CMY, YI

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