brief discussion on some topics of computer graphics

1. C. Graphics
Key Board
Flat Panel Display
Conversion Between HSV and
RGB
LCD, Plasma
LED

2. KEYBOARD
• Primary device for entering text string
• Input non-graphics data
• Features:- Cursor-Control, Function Keys
• Other features:- menu selection, graphics function, screen
coordinate
• Buttons, dials and switches are used to give the input to
graphic application

3. FLAT-PANEL DISPLAY
• Video devices with reduced volume, weight and power
• Portable
• Applications:- TV monitors, Calculators, laptops etc.
• Can hangs on walls and wear in wrists
• Two types
Emissive Display
Non-Emissive Display

4. LED
• Light Emitting Diode
• Matrix of diodes are arranged to form a display pattern
• Picture definition stored in refresh buffer
• Information are extracted from buffer and converted to voltage
level and applied to diode to produce light in the display

5. PLASMA
• Plasma is also called gas-discharge display.
• It is constructed by filling region between two glass plates with a
mixture of gases that usually include neon .
• The space between these two ribbon includes gases.
• when firing voltage is applied the effect of vertical and horizontal
ribbon causes the gas to break down that produce glowing plasma of
electron and ion.
• Picture definition is stored in refresh buffer and firing voltage is
applied to refresh the pixel position 60 times per second.

6. LCD
1. System that use LCD have less volume, less weight, less power consumption.
2. The term liquid crystal refers to the fact that these compound have crystalline arrangement of
molecules, yet they flow like liquid.
3. Flat panel display commonly use nematic liquid crystal compound that tend to keep the long axes of
rod-shaped molecules aligned.
4. LCD works with light.
5. There are few component in one pixel of LCD they are : Back Light, Polarizer(Horizontal, Vertical),
LCD, RGB.
6. At first the light transmit from back light to polarizer (Horizontal, Vertical) which filters vertical light if
it is horizontal polarizer and filters horizontal light if it is vertical polarizer.
7. Then the light transmit to LCD which changes from horizontal to vertical or vice-versa of which the
other end of polarizer is able to receive the light form transmitted by LCD.

7. LCD CONTD..
8. At the second polarizer it receives light , filters it and passes it next.
9. After that the light is received by RGB which gives the light according to the light received.
10. RGB has 256 values each from 0-255 which gives combination of several colors.
11. LCD it self contains three components . They are : Glass plate , Electrode, LCD molecules.
12. When electrode is inactive the form of light of changed.
13. When electrode is active the molecules changes its form which results that the LCD does not change
light from horizontal - vertical or vice versa .
14. After that the receiving polarizer cannot receive the light.
15. That results in RGB also not receiving the light where the value of RGB will be 0,0,0 which results in
forming the color black.
16. If the value of RGB will be 255,255,255 it forms white color

8. CONVERSION BETWEEN HSV AND
RGB

9. HSV TO RGB
void hsvTorgb( float *r, float *g, float *b, float h, float s, float v )
{
int i;
float f, p, q, t;
if( s == 0 ) { // achromatic (grey)
*r = *g = *b = v;
return;
}
h /= 60; // sector 0 to 5
i = ffloor( h );
f = h - i; // factorial part of h
p = v * ( 1 - s );
q = v * ( 1 - s * f );
t = v * ( 1 - s * ( 1 - f ) );

10. HSV TO RGB CONTD..
switch( i ) {
case 0:
*r = v;*g = t;*b = p;
break;
case 1:
*r = q;*g = v;*b = p;
break;
case 2:
*r = p;*g = v;*b = t;
break;
case 3:
*r = p;*g = q;*b = v;
break;

11. HSV TO RGB CONTD..
case 4:
*r = t;*g = p;*b = v;
break;
Case 5:
*r = v;*g = p;*b = q;
break;
}
}

12. RGB TO HSV
// r,g,b values are from 0 to 1
// h = [0,360], s = [0,1], v = [0,1]
void rgbTohsb( 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;
return;
}

13. RGB TO HSV CONTD..
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;
}

14. THANK
YOU