HSL & HSV COLOUR MODELS

- SALIL SULEY (66)DENCIN VAZHAPPILLY (67)

ROHAN VEMULA (68)VISHNU RC VIJAYAN (69)

SHREE WARANG (70)MAHESHKUMAR YADAV (71)

HSL COLOUR MODEL

Hue, saturation and lightness

Most commonly used cylindrical coordinate system for representing RED GREEN BLUE color model

It was developed in 1970 for computer graphics applications, color pickings and image editing softwares

TERMINOLOGIES

Hue : The angle around the central vertical axis corresponds to hue

Saturation : The distance from the central axis corresponds to saturation. (0%-Grey & 100%-Full sat)

Lightness :The distance along the central axis corresponds to lightness. (0%-Black & 100%-White)

PRINCIPLES

HSL tries to be more intuitive than the general Cartesian color representation

HSL helps us to bridge the RGB color model , understood by computers, to mix colors more like humans do

HSL COLOUR ATTRIBUTESHue:- It refers to pure spectrum of colours, without tint

or shade. colours with same hue are distinguished with their lightness.eg- light blue

Saturation:- measurement of how different from pure grey the colour is perceived saturation depends on the surrounding in which colour is seen

Luminosity:-brightness of area judged relative to brightness of similarly illuminated area which appears to be bright

HSL SCALEo Hue is represented as angle of colour circle, given as unit less number.

Red=0=360, Green=120,Blue=240

o Saturation & luminosity is represented in percentage, o 100% is full saturationo 0% is shade of greyo 100% luminosity is whiteo 50% luminosity is normalo 0% luminosity is black

HSL REPRESENTATION HSL is represented as two cones within the

cyclinder

LUMINOSITY

SATURATION

100 075 3350 10025 330 0

HSL AND RGB CONVERSION

HSL, HEX AND RGB CO-ORDINATES FOR PROMINENT COLOURS

ADVANTAGES OF HSL

The HSL model keeps the light and saturation aspects of the color model unique from each other, it tends to be more useful for those wishing to take advantage of these attributes in their work

Light can range from white to black in a HSL model (with the desired color in between), while the similar HSV color model can only range from the desired color to black

It is user-oriented. Therefore colour selection and image colour adjustment can be done faster with greater ease

DISADVANTAGES While choosing a single color, they ignore much of the complexity of

color appearance

Because hue is a circular quantity, represented numerically with a discontinuity at 360°, it is difficult to use in statistical computations or quantitative comparisons

Analysis requires the use of circular statistics

Since computational capacity has increased tremendously over the past few decades, better alternative colour models are available for greater visual accuracy and perceptual relevance

HSV COLOUR MODEL

HSV are the most common cylindrical-coordinate representations of points in an RGB colour model

HSV stands for hue, saturation, and value

Hue, Saturation, Value or HSV is a colour model that describes colours (hue or tint) in terms of their shade (saturation or amount of gray) and their brightness (value or luminance)

PRINCIPLE Cylindrical geometries with hue, their angular dimension, starting at

the red primary at 0°, passing through the green primary at 120° and the blue primary at 240°, and then wrapping back to red at 360°

The two representations rearrange the geometry of RGB in an attempt to be more intuitive and perceptually relevant ,based on the color wheel

Saturation (s) of the color ranges from 0 to 100%. Also sometimes, it called the "purity". The lower the saturation of a color, the more "grayness" is present and the more faded the color will appear

Value (v) of the color ranges from 0 to 100%. It is a nonlinear transfor(v), the brightness mation of the RGB color space. Note that HSV and HSB are the same

HSV SCALE Hue angles: 0=Red, 120=Green, 240=Blue. Saturation: 0 at the centre (no saturation,

which makes no real colouring) to 1 at the edge (full saturated colours).

Value: From 0 at the bottom (no colour, or black) to 1 at the top.

PROGRAM TO CONVERT RGB TO HSV

// r,g,b values are from 0 to 1 // h = [0,360], s = [0,1], v = [0,1] // if s == 0, then h = -1 (undefined)void RGBtoHSV( float r, float g, float b, float *h, float *s, float *v ) { float min, max, delta; min = MIN( r, g, b ); max = MAX( r, g, b ); *v = max; // v delta = max - min; if( max != 0 ) *s = delta / max; // s else {

// r = g = b = 0 // s = 0, v is undefined *s = 0; *h = -1; return; } if( r == max ) *h = ( g - b ) / delta; // between yellow & magenta else if( g == max ) *h = 2 + ( b - r ) / delta; // between cyan & yellow else *h = 4 + ( r - g ) / delta; // between magenta & cyan *h *= 60; // degrees if( *h < 0 ) *h += 360;}

REFERENCES

Websites

1. https://en.wikipedia.org/wiki/HSL_and_HSV2. www.lps.usp.br/hae/apostila/basico/HSI-wikipedia.pdf3. www.ics.uci.edu/~majumder/vispercep/colviz.pdf4. www.slideshare.net/EngHaitham/color-models-42915934