HSL & HSV colour models

1. HSL & HSV COLOUR MODELS
- SALIL SULEY (66)
DENCIN VAZHAPPILLY (67)
ROHAN VEMULA (68)
VISHNU RC VIJAYAN (69)
SHREE WARANG (70)
MAHESHKUMAR YADAV (71)

2. 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

3. 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)

4. 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

5. HSL COLOUR ATTRIBUTES
 Hue:- 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

6. HSL SCALE
o 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 saturation
o 0% is shade of grey
o 100% luminosity is white
o 50% luminosity is normal
o 0% luminosity is black

7. HSL REPRESENTATION
 HSL is represented as two cones within the
cyclinder
LUMINOSIT
Y
SATURATIO
N
100 0
75 33
50 100
25 33
0 0

8. HSL AND RGB CONVERSION

9. HSL, HEX AND RGB CO-ORDINATES FOR PROMINENT COLOURS

10. 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

11. 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

12. 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)

13. 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

20. 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.

21. 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 {

22. // 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;
}

24. REFERENCES
 Websites
1. https://en.wikipedia.org/wiki/HSL_and_HSV
2. www.lps.usp.br/hae/apostila/basico/HSI-wikipedia.pdf
3. www.ics.uci.edu/~majumder/vispercep/colviz.pdf
4. www.slideshare.net/EngHaitham/color-models-42915934