Understanding Display Technology: Resolution, Aspect Ratio, and Scan Methods

1. Resolution

Resolution refers to the number of pixels used to display an image on a screen. It determines the clarity and detail of the image.

• It is usually written as width × height (e.g., 1920 × 1080).
• The higher the resolution, the sharper and clearer the image.
• Lower resolution images appear blurry or pixelated.

Example: If a display has a resolution of 1024 × 768, it means the screen contains 1024 pixels horizontally and 768 pixels vertically.

2. Aspect Ratio

Aspect Ratio is the ratio between the width and height of a display screen or image. It defines the shape of the display area and is expressed as width : height.

Common Aspect Ratios:

• 4 : 3 – Old computer monitors and televisions
• 16 : 9 – Modern widescreen monitors and TVs
• 21 : 9 – Ultra-wide displays

Example: A resolution of 1920 × 1080 has an aspect ratio of 16 : 9.

3. Persistence

Persistence in computer graphics refers to the time a pixel continues to glow on the screen after the electron beam is removed. It is primarily related to CRT (Cathode Ray Tube) displays and determines how long an image remains visible.

Types of Persistence:

• Low Persistence: The image fades quickly and requires frequent refreshing.
• High Persistence: The image stays longer on the screen but may cause blurring or ghosting.

Example: In CRT monitors, the screen must be refreshed many times per second to maintain the image due to persistence.

4. Raster Scan Display

A Raster Scan Display is a technique where the electron beam scans the screen line by line from top to bottom. The screen is divided into a grid of pixels, where each pixel stores color and intensity information.

• The beam starts at the top-left, moves horizontally, and proceeds line by line to the bottom.
• This process repeats many times per second, a cycle known as refreshing.
• Examples: Televisions, modern computer monitors, and LCD screens.

Advantages

• Can display complex images and filled shapes.
• Suitable for photographic images and shading.

Disadvantages

• Requires large memory (frame buffer).
• May produce jagged edges (aliasing).

5. Random Scan Display

A Random Scan Display (also called Vector Display) is a technique where the electron beam draws only the required lines directly on the screen instead of scanning the entire area. The beam moves randomly from point to point to draw images as a collection of vectors.

• Images are stored as line-drawing commands.
• Examples: Flight simulators, engineering drawing systems, and CAD systems.

Advantages

• Produces smooth and high-quality lines.
• Requires less memory for line drawings.

Disadvantages

• Cannot display complex filled images easily.
• Not suitable for realistic pictures.