Graphics Systems and Models in Visual Communication

1. Graphic Systems, Lighting, and Models

2. Why do we need graphics? • To convey information • Simulation • User interfaces

3. A Graphics System • Input devices • Processor • Memory • Frame buffer • Output devices

4. The Frame Buffer • Is an array – the raster – that holds graphics related information • Mostly, it holds pixels • Converting geometric entities to pixel information is called rasterization • Each pixel in a picture requires color data • The number of bits used is called its depth • The depth determines how many different colors an image can have

5. 24-bit (true color)

6. 8-bit (256 colors)

7. 4-bit (16 colors)

8. 3-bit (8 colors)

9. 8-bit Grayscale

10. Color Pallet • Non-true color images store the color values in pallets • Pallets are an array of colors stored, usually, at the beginning of an image file • The color information of a particular pixel is stored as an index reference to the pallet

11. Example pallet

12. True Color • 24-bit images • use 3, 8-bit segments to encode the three primaries: Red, green, and blue (RGB) • Each 8-bit segment can, therefore, hold 256 shades of that color • This results in a possible 16,777,216 different colors

13. Output Devices • The first, and still most widely used, is the cathode-ray tube (CRT)

14. More on CRTs

15. LCD Displays

16. The human element • If a computer draws a picture and there is no one there to see it, was it pretty? • Was it even a picture? The purpose of graphics is to be viewed by humans

17. The human visual system • Light enters the eye through the lens and cornea • The iris opens and closes to regulate the amount of light coming in

18. The human visual system • An inverted 2D image is produced on the retina • Sensor apparatuses called rods and cones detect features of the light that strike them

19. The human visual system • The rods and cones then send their signal down the optic nerve to the visual cortex of the brain

20. The human visual system • We can see electromagnetic energy in the frequency range of 350 to 780 nm

21. The human visual system • The sizes of the rods and cones along with properties of the lens and cornea determine our visual resolution • Resolution is the measure of how close we can place two points and still recognize that there are two distinct points

22. The human visual system • There are three different types of cones that respond to different wave lengths of light

23. The human visual system • The intensity of an image is the physical amount of light • The brightness of an image is the perceived amount of light

25. We live in a 3D world • Because of binocular vision

26. Ray tracing • A point source (of light) is the engine

27. Synthetic-Camera Model • If we imagine a camera taking a picture of our virtual scene, we must consider many different aspects of what that camera might see

28. Next class Beginnings of graphics programming