JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year COMPUTER GRAPHICS Previous Question Paper (February - 2022 - R16)

A Cathode Ray Tube (CRT) is the primary output device used in early computer graphics systems to display images. It operates by firing a beam of electrons from an electron gun toward a phosphor-coated screen.

The main components are:

• Electron Gun: Produces a focused stream of electrons through heating a cathode.
• Control Electrode: Regulates the intensity of the electron beam, determining the brightness of the pixel.
• Focusing and Deflection Systems: Use electromagnetic or electrostatic fields to focus the beam into a tight point and steer it to specific coordinates on the screen.
• Phosphor-coated Screen: Emits light when struck by the high-velocity electron beam.

In Raster Scan systems, the beam sweeps across the screen row by row, while in Random Scan systems, the beam is directed only to the specific paths required to draw the lines of the image.

The Digital Differential Analyzer (DDA) is a scan-conversion line algorithm based on calculating either Δy or Δx. The steps are:

1. Calculate Δx = x2 - x1 and Δy = y2 - y1.
2. Determine the number of steps: if |Δx| > |Δy|, steps = |Δx|; otherwise, steps = |Δy|.
3. Calculate increments: x_inc = Δx / steps and y_inc = Δy / steps.
4. Starting at (x1, y1), iterate 'steps' times: x = x + x_inc, y = y + y_inc, and plot round(x), round(y).

Advantages: It is a simpler algorithm than Bresenham's, avoids multiplication, and is faster than the direct line equation method because it uses incremental calculations.

Disadvantages: It involves floating-point arithmetic (rounding and addition), which is computationally expensive and can lead to cumulative rounding errors over long lines, causing the line to drift from the true path.