How a Monitor Works

Raster Cathode Ray Tubes (CRTs)

most common display device

• Capable of high resolution.
• Good colour fidelity.
• High contrast (100:1).
• High update rates.

Electron beam scanned in regular pattern of horizontal scanlines.

Raster images

are stored in a frame buffer.

Frame buffers

are composed of VRAM (video RAM).

VRAM

is dual-ported memory capable of

• Random access
• Simultaneous high-speed serial output: built-in serial shift register can output entire scanline at high rate synchronized to pixel clock.

At each pixel in scanline, intensity of electron beam modified by the pixel value being shifted synchronously out of VRAM.

Colour CRTs

have three different colours of phosphor and three independent electron guns.

Shadow Masks

allow each gun to irradiate only one colour of phosphor.

\

Colour is specified either

• Directly, using three independent intensity channels, or
• Indirectly, using a Colour Lookup Table (LUT).

In the latter case, a colour index is stored in the frame buffer.

Reading: Hearn and Baker, Chapter 2. Red book, Chapter 4. White book, Chapter 4.