13.003 Computational Geometry and Visualization
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.
- 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").
On to "Graphics Software"
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