created by : Sudipta mondal faculty of BCET

1. Colour Models and its Application HLS and YIQ AnirbanSaha Third year Computer Science and Technology Bengal College of Engineering and Technology 1

2. Modules: 2 Prerequisite : Frequency, Light, Dominant frequency, Definitions. YIQ model: Introduction, Application. HLS model: Introduction, Discussion, Application.

4. Violet: 7.5 x 1014 hertzR-O-Y-G-B-I-V Wavelength (700 nm) Wavelength (400 nm) Lowest Frequency Highest Frequency Requisites: 3

5. 4 HUE BRIGHTNESS SATURATION COLOUR, DOMINENT FREQUENCY PERCIEVED INTENSITY OF LIGHT THE WASHING OUT EFFECT ED = DOMINENT LIGHT. ENERGY DENSITY EW = ENERGY DENSITY OF WHITE LIGHT AREA UNDER THE CURVE -> BRIGHTNESS MORE THE VALUE OF (ED-EW) PURER IS THE COLOUR

6. 5 Some more terms: The dimensions of the HSV and HSL geometries, simple transformations of the not-perceptually-based RGB model, are not directly related to the photometric color-making attributes of the same names, as defined by scientists, for instance by the CIE or ASTM. Nonetheless, it is worth reviewing those definitions before leaping into the derivation of our models. Hue is the “attribute of a visual sensation according to which an area appears to be similar to one of The perceived colors: red, yellow, green, and blue, or to a combination of two of them”. Intensity or radiance is the total amount of light passing through a particular area. Luminance, denoted Y and measured in cd/m2, is the radiance weighted by the effect of each wavelength on a typical human observer. Often the term luminance is used for the relative luminance, Y/Yn, where Yn is the luminance of the reference white point. Luma is the weighted sum of gamma-corrected R′, G′, and B′ values, denoted Y′, and used in Y′CbCr, for JPEG compression and video transmission. Brightness is the “attribute of a visual sensation according to which an area appears to emit more or less light”. Lightness or value is the “brightness relative to the brightness of a similarly illuminated white”. Colorfulness is the “attribute of a visual sensation according to which the perceived color of an area appears to be more or less chromatic”. Chroma is the “colorfulness relative to the brightness of a similarly illuminated white”. Saturation is the “colorfulness of a stimulus relative to its own brightness”. Brightness and colorfulness are absolute measures, which usually describe the spectral distribution of light entering the eye, while lightness and chroma are measured relative to some white point, and are thus often used for descriptions of surface colors, remaining roughly constant even as brightness and colorfulness change with different illumination. Saturation = colorfulness/brightness = chroma/lightness.

7. YIQ model 6

8. National Television System Committee Used in NTSC - TV monitors, using one composite signal. RGB model requires 3 separate signals to form an image. It is based on the CIE and the XYZ colour models. NTSE: Analog television system used in most of North America, South America, Japan, South Korea, Taiwan, Burma, and some Pacific island nations and territories (see map). NTSC is also the name of the U.S. standardization body that developed the broadcast standard 7

9. Y I Q Luminance (Brightness information) Orange-Cyan hue Chromaticity Information (hue and purity) Green - Magenta 8 “Y” stands for Luminance “I” stands for inphase “Q” stands for quadrature referring to the components of the quadrature amplitude modulation

10. RGB  YIQ [TV signal using NTSC encoder] 9 = YIQ  RGB [TV signal using NTSC Decoder] = 9

11. HSV and HSL models 10

12. RGB : It explores a wide range of colors Possible by mixing three colours… Constitutes of Red Green and Blue. but it fails to match the intuitions of human psychology. Why? Because, when we imagine a colour… our intuitions bring with it The aspects of lightness of the colour and the amount we use to colour a specific region. 11

13. Result: H S V H S L ue ue aturation aturation alue ightness Introduced in 1979 By Tektronix Inc … and has been used since then Mid 1970’s by pioneers of PARC and NYIT Discussed in Aug 1978 12

14. Application: >Aid selection >Colour Selection >ColourComparision >Modification of Colour >Image analysis …in all picture editing softwares and in designing. 13

15. HLS: Represented by a double hexagonal Cone, with WHITE at the top and BLACK at the bottom. The HUE lies on the circle, LIGHTNESSgradually increases from Black to White SATURATION increases from centre to the periphery 14

16. 15 Hue specifies the angle about the vertical axis that locates the specific hue. The colours are specified around the perimeter of the cone. Complementary colours are 180 degrees apart The vertical axis is called the “Lightness”

17. 16 Thank You. AnirbanSahaPh: 9903055542 Third year email: saha.a2006@gmail.com Computer Science and Technology Blog at: http://sahaanirban.wordpress.com Bengal College of Engineering and Technology Twitter: @sahaanirban