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# Colour models

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### Colour models

1. 1. Colour Models and its Application<br />HLS and YIQ<br />AnirbanSaha<br />Third year<br />Computer Science and Technology<br />Bengal College of Engineering and Technology<br />1<br />
2. 2. Modules:<br />2<br />Prerequisite : Frequency, Light, Dominant frequency, Definitions.<br />YIQ model: Introduction, Application.<br />HLS model: Introduction, Discussion, Application. <br />
3. 3. Visible Light: <br /><ul><li>Red: 4.3 x 1014 hertz
4. 4. Violet: 7.5 x 1014 hertz</li></ul>R-O-Y-G-B-I-V<br />Wavelength<br />(700 nm)<br />Wavelength<br />(400 nm)<br />Lowest <br />Frequency<br />Highest<br />Frequency<br />Requisites:<br />3<br />
5. 5. 4<br />HUE<br />BRIGHTNESS<br />SATURATION<br />COLOUR, DOMINENT FREQUENCY<br />PERCIEVED INTENSITY OF LIGHT<br />THE WASHING OUT EFFECT<br />ED = DOMINENT LIGHT. ENERGY DENSITY<br />EW = ENERGY DENSITY OF WHITE LIGHT<br />AREA UNDER THE CURVE -> BRIGHTNESS<br />MORE THE VALUE OF (ED-EW) PURER IS THE COLOUR<br />
6. 6. 5<br />Some more terms:<br />The dimensions of the HSV and HSL geometries, simple transformations of the not-perceptually-based <br />RGB model, are not directly related to the photometric color-making attributes of the same names, <br />as defined by scientists, for instance by the CIE or ASTM. Nonetheless, it is worth reviewing those definitions <br />before leaping into the derivation of our models.<br />Hue is the “attribute of a visual sensation according to which an area appears to be similar to one of <br /> The perceived colors: red, yellow, green, and blue, or to a combination of two of them”.<br />Intensity  or radiance is the total amount of light passing through a particular area.<br />Luminance, denoted Y and measured in cd/m2, is the radiance weighted by the effect of each <br /> wavelength on a typical human observer. Often the term luminance is used for the relative<br /> luminance, Y/Yn, where Yn is the luminance of the reference white point.<br />Luma is the weighted sum of gamma-corrected R′, G′, and B′ values, denoted Y′, and used in Y′CbCr, <br /> for JPEG compression and video transmission.<br />Brightness is the “attribute of a visual sensation according to which an area appears to emit more or <br /> less light”.<br />Lightness or value is the “brightness relative to the brightness of a similarly illuminated white”.<br />Colorfulness is the “attribute of a visual sensation according to which the perceived color of an area <br /> appears to be more or less chromatic”.<br />Chroma is the “colorfulness relative to the brightness of a similarly illuminated white”.<br />Saturation is the “colorfulness of a stimulus relative to its own brightness”.<br />Brightness and colorfulness are absolute measures, which usually describe the spectral distribution <br /> of light entering the eye, while lightness and chroma are measured relative to some white <br /> point, and are thus often used for descriptions of surface colors, remaining roughly <br /> constant even as brightness and colorfulness change with different illumination. <br /> Saturation = colorfulness/brightness = chroma/lightness.<br />
7. 7. YIQ<br />model<br />6<br />
8. 8. National Television System Committee<br />Used in NTSC - TV monitors, using one composite signal.<br /> RGB model requires 3 separate signals to form an image.<br />It is based on the CIE and the XYZ colour models.<br />NTSE: <br />Analog television system used in most of North America,<br />South America, Japan, South Korea, Taiwan, Burma, and some<br /> Pacific island nations and territories (see map). <br />NTSC is also <br />the name of the U.S. standardization body that developed the <br />broadcast standard<br />7<br />
9. 9. Y<br />I<br />Q<br />Luminance <br />(Brightness information)<br />Orange-Cyan hue<br />Chromaticity Information <br />(hue and purity)<br />Green - Magenta<br />8<br />“Y” stands for Luminance<br />“I” stands for inphase<br />“Q” stands for quadrature<br />referring to the components <br /> of the quadrature amplitude modulation<br />
10. 10. RGB  YIQ [TV signal using NTSC encoder] <br />9<br />=<br />YIQ  RGB [TV signal using NTSC Decoder] <br />=<br />9<br />
11. 11. HSV and HSL <br />models<br />10<br />
12. 12. RGB :<br />It explores a wide range of colors <br />Possible by mixing three colours…<br />Constitutes of Red Green and Blue.<br />but it fails to match the <br />intuitions of human psychology.<br />Why?<br />Because, when we imagine a colour… our intuitions bring with it <br />The aspects of lightness of the colour and the amount we use to<br />colour a specific region.<br />11<br />
13. 13. Result:<br />H<br />S<br />V<br />H<br />S<br />L<br />ue<br />ue<br />aturation<br />aturation<br />alue<br />ightness<br />Introduced in 1979<br />By Tektronix Inc<br />… and has been used since then<br />Mid 1970’s <br />by pioneers of <br />PARC and NYIT<br />Discussed in<br /> Aug 1978<br />12<br />
14. 14. Application:<br />>Aid selection<br />>Colour Selection<br />>ColourComparision<br />>Modification of Colour<br />>Image analysis<br />…in all picture editing <br />softwares and in designing.<br />13<br />
15. 15. HLS:<br />Represented by a double hexagonal<br />Cone, with WHITE at the top and <br />BLACK at the bottom.<br />The HUE lies on the circle, LIGHTNESSgradually increases <br />from Black to White<br />SATURATION increases <br />from centre to the periphery<br />14<br />
16. 16. 15<br />Hue specifies the angle about the vertical axis <br />that locates the specific hue.<br />The colours are specified around the <br />perimeter of the cone.<br />Complementary colours are 180 degrees apart<br />The vertical axis is called the “Lightness”<br />
17. 17. 16<br />Thank You.<br />AnirbanSahaPh: 9903055542<br />Third year email: saha.a2006@gmail.com<br />Computer Science and Technology Blog at: http://sahaanirban.wordpress.com<br />Bengal College of Engineering and Technology Twitter: @sahaanirban<br />