Tones and tints, Computer Graphics

Q. What is the difference between tones and tints? Which one component of YIQ color model does black- and- white television use? How can you convert a ZTSC video signal to an RGB signal? Also write the relevant matrix transformation. Explain the CMY color model. 

Tones and tints: An artist creates a color painting by mixing color pigments with white and black pigments to form the various shades, tints and tones in the scene. Starting with the pigment for a "pure color" the artist adds a black pigment to produce different shades of that color. The more black pigment, the darker the shade. Similarly, different tints of the color are obtained by adding a white pigment to the original color, making it lighter as more white is added. Tones of the color are produced by adding both black and white pigment. YIQ color model Whereas an RGB monitor requires separate signals for the red, green, and blue components of an image, a television monitor uses a single composite signal. The National Television System Committee (NTSC) color model for forming the composite video signal is the YIQ model, which is based on concept s in the CIE XYZ model. In the YIQ color model, parameter Y is the same as in the XYZ model. Luminance information is contained in the Y parameter, while chromaticity information is incorporated into the and Q parameters. A combination of red green and blue intensities is chosen for the Y parameter to yield the standard luminosity curve. Since Y contains the luminance information black and white television monitors use only the Y shaped. The largest bandwidth in the NTSC video signal is assigned to the Y information. Parameter contains orange cyan hue information that provides the flesh tone shading and occupies a bandwidth of approximately 1.5 MHz. Parameter Q carries green magenta hue information in a bandwidth of about 0.6 MHz. Conversion of NTSC signal t an RGB signal An RGB signal can be converted to a television signal using as NTSC encoder, which converts RGB values to YIQ values, then modulates and superimposes the I and Q information on the Y signal. The conversion from RGB values to YIQ values is accomplished with the transformation. This transformation is based on the NTSC standard RGB phosphor, whose chromaticity coordinate were given in the preceding section. The larger proportions of red and green assigned to parameter Y indicate the relative importance of these hues in determining brightness, compared to blue. An NTSC video signal can be converted to an RGB signal using an NTSC decoder, which separates the video signal into the YIQ components, then converts to RGB values. We convert from YIQ space with the inverse matrix transformation from Eq. (i): CMY color model A color model defined with the primary colors Cyan, Magenta, and Yellow (CMY) is useful for describing color output to hard- copy devices. Unlike video monitors, which produce a color pattern by combining light from the screen phosphors, hard- copy devices such as plotters produce a color picture by coating a paper with color pigments. We see the color by reflected light, a subtractive process. As we have noted, cyan can formed by adding green and blue light. Therefore, when white light is reflected from cyan- colored ink, the reflected light must have no red component. That is. Red light is absorbed, or subtracted, by the ink. Similarly, magenta ink subtracts the green component from incident light, and yellow subtracts the blue component. A unit cube representation for the CMY model is illustrated in Fig. In te CMY model, point (1,1, 1) represents black, because all components of the incident light are subtracted. The origin represents white light. Equal amounts of each of the primary colors produce grays, along the main diagonal of the cube. A combination of cyan and magenta ink produce blue light, because the red and green components of the incident light are absorbed. Other color combination are obtained by a similar subtractive process. The printing process often used with the CMY model generates a color point with a collection of four ink dots, somewhat as an RGB monitor uses a collection of three phosphor doth. One dot is used for each of the primary colors (cyan, magenta, and yellow), and one dot is black. A black dot is included because the combination of cyan, magenta, and yellow inks typically produce dark gray instead of black. Some plotters produce different color combination by spraying the ink for the three primary colors over each other and allowing them to mix before they dry. We can express the conversion from an RGB representation to a CMY representation with the matrix transformation where the white is representation In the RGB system as the unit column vector. Similarly, we convert from a CMY color representation to an RGB representation with the matrix transformation where black is representation in the CMY system as the unit column vector.  

Posted Date: 7/12/2012 6:45:38 AM | Location : United States







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