Colormodels

Colormodels

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  Computer Graphics Color Models 1 PreparedBy : Prakshal Trivedi (160110116055) Tejoy Vachhrajani (160110116057) Bhavik Vashi (160110116061) Batch : 1D16 Submitted To : Prof. Prem Balani
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  3 Properties of Light Eachfrequency value within the visible region of the electromagnetic spectrum corresponds to a distinct spectral color. FIGURE-1
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  4 • When whitelight is incident on an opaque object , some frequencies are reflected and some are absorbed. • The combination of frequencies present in the reflected in the reflected light determines the color of the object that we see.(Dominant frequency or Hue) Properties of Light
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  5 Period (T) Properties ofLight
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  6 Characteristics of Color 1. DominantFrequency (Hue) The color we see (red, green, purple). 2. Brightness The total light energy, how bright is the color (How bright are the lights illuminating the object?) 3. Purity (Saturation) Purity describes how close a light appears to be to a pure spectral color, such as pink is less saturated than red. Chromaticity refers to the two properties (purity & hue) together.
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  7 •A color modelis an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. [Wikipedia] •Any method for explaining the properties or behavior of color within some particular context is called a Color Model.[Hearn, Baker ,computer graphics with OpenGL] Color Model
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  8 Color Model Primary Colors Setsof colors that can be combined to make a useful range of colors Color Gamut Set of all colors that we can produce from the primary colors. Complementary Colors Pairs of colors which, when combined in the right proportions, produce white. Example, in the RGB model: red & cyan , green & magenta , blue & yellow. •No finite set of real primary colors can be combined to produce all possible visible colors. •However, given a set of three primary colors, we can characterize any fourth color using color-mixing processes.
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  9 Shades , Tints& Tones • A shade is produced by “dimming ” a hue.[Adding black]. Dark Blue = pure blue + black • A tint is produced by "lightening" a hue. [Adding white]. Pastel red = pure red + white • Tone refers to the effects of reducing the "colorfulness" of a hue. [adding gray] or [adding black & white]. Thus, shading takes a hue toward black, tinting takes a hue towards white, and tones cover the range between. Color Model
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  10 Color Model Additive color Useslight to display color. Mixing begins with black and ends with white; as more color is added, the result is lighter and tends to white. Used for computer displays Example: The RGB colors are light primaries and colors are created with light. A subtractive color Uses ink to display color. Mixing means that one begins with white and ends with black; as one adds color, the result gets darker and tends to black. Used for printed material It is called 'subtractive' because its wavelength is less than sum of the wavelengths of its constituting colors. Example: The CMYK color system is the color system used for printing.
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  16 •The red, green,and blue (RGB) color space is widely used throughout computer graphics. •Additive Color Model. •Unit Cube defined on R, G & B axes. •The Origin (0,0,0) represents black and the diagonally opposite vertex (1,1,1) is White. •Vertices of the cube on the axes represent primary colors, and the remaining vertices are the complementary color points for each of the primary colors. •Shades of gray are represented along the main diagonal. RGB Model
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  17 Each color pointwithin the unit cube can be represented as w weighted vector sum of the primary colors, using unit vectors R,G and B. C(λ) =(R,G,B) = RR +GG+ BB Where R,G, and B are assigned values in the range from 0 to 1.0. For example , the magenta vertex is obtained by adding the maximum red and blue values to produce : (1,0,1) RGB Model
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  18 YIQ model •YIQ modelis used for US TV broadcast. •This model was designed to separate chrominance (I and Q) from luminance (Y). •This was a requirement in the early days of color television when black-and-white sets still were expected to pick up and display what were originally color pictures •The Y-channel contains luminance information (sufficient for black-and-white television sets) while the I and Q channels carried the color information.
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  19 •A color televisionset would take these three channels, Y,I, and Q, andmap the information back to R, G, and B levels for display on a screen. •The advantage of this model is that more bandwidth can be assigned to the Y-component (luminance) because the human visual system is more sensitive to changes in luminance than to changes in hue or saturation YIQ model Convert From RGB ToYIQ Convert From YIQ ToRGB
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  20 HSV Model Every coloris represented by three components Hue ( H ), Saturation ( S ) and Value ( V )
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  21 HSV Model The Hue(H) of a color refers to which pure color it resembles. All tints, tones and shades of red have the same hue. (simply the color we see)
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  22 HSV Model The Saturation(S) of a color describes how white the color is. Or the amount of white added to the color. A pure red is fully saturated (S=1) means no white added
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  23 HSV Model The Value(V) of a color, also called its lightness, describes how dark the color is. A value of 0 is black, with increasing lightness moving away from black.
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  24 HSL Model • Double-coneRepresentation Parameters are : • Hue (H) • Lightness (L) • Saturation (S)
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  25 HSL Model • VerticalAxis is called Lightness(L). • At L=0 we have black , and at L=1 we have white • Grayscale values are along the L axis • The pure colors lie at the axis where L=0.5 and S=1.0
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  26 •Subtractive Color Model. •Standsfor cyan-magenta-yellow. •Used for hardcopy devices (ex. Printers). •A printed color that looks red absorbs the other two components G and B and reflects R. •Thus the C-M-Y coordinates are just the complements of the R-G-B coordinates. CMY and CMYK Model
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  27 CMY and CMYKModel In additive color models such as RGB, white is the “additive” combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is the opposite: white is the natural color ofthe paper or other background, while black results from a full combination of colored inks. RGB To CMY CMY To RGB
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  28 CMYK Color Model Althoughcyan, magenta and yellow inks might be expected be sufficient for color printing, most actual color printing uses black ink in addition. This is partly because a mixture of the first three inks may not yield a black that is neutral enough, or dark enough, but also because the use of black spares the use of the more expensive colored inks, and also reduces the total amount of ink used, thus speeding drying times. K used instead of equal amounts of CMY •called under color removal •richer black • less ink deposited on paper – dries more quickly •First approximation – nonlinearities must be accommodated: K = min(C, M, Y) C’ = C – K M’ = M – K Y’ = Y – K CMY and CMYK Model
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  Color Model ApplicationAreaColor Model ApplicationArea RGB - Computer graphics - Image processing - Image Analysis - Image Storage CMY(K) Printing HSV, HSL - Human visual perception - Computer graphics processing - Computer Vision - Image Analysis - Design image - Human vision - Image editing software - Video editor YIQ - TV broadcasting - Video system Color Models Applications
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