13.016 Introduction to Geometric Modeling and Computation

Graphics Hardware

Vector

Displacement of an electron beam across the phosphor coated face of a CRT, producing a continuous line.

Short persistence phosphor
- Requires continual refresh.
Direct View Storage Tube (DVST)
- No refresh necessary.
- A metallic grid behind the CRT surface captures and stores the image.

Raster

The phosphor coated face of a CRT is divided into discrete pixels, as in TV.

Frame buffer
- A memory location is reserved to specify the status of each pixel.
- The horizontal sequence of pixels is called a scan line.
Refresh rate
- TV refresh rate of 30 Hz requires interlacing.
- A minimum refresh of 60 Hz fuses the picture into a steady image.
Color
- One bit per pixel allows black and white (off and on).
- In general, n bits allows 2^n gray values from black to white.
- If each pixel is comprised of three pieces of phosphor, one each red, green, and blue, and if three separate values are stored in the frame buffer for the pixel, a variety of colors can be produced.
- Instead of using the frame buffer to specify the color directly (RGB mode), it can function as an index into a table of colors (Indexed mode). This table is called a color lookup table.
Aliasing
- A raster image is a discrete sampling.
- Horizontal and vertical lines can be drawn correctly; diagonals or curves can only be drawn approximately ("jaggies" or "stairstepping").