How It Works: A raster scan display works by painting an image on the screen pixel by pixel, row by row. It follows a systematic pattern where the electron beam (in CRT monitors) or the display elements (in modern LCD/LED screens) sweep across the screen from left to right, top to bottom, in a series of horizontal lines (scan lines). This process is akin to how a traditional TV screen works.
Process: The display draws the image starting from the top-left corner, moving to the right, then moves to the next row below, and repeats this process until the entire screen is filled. This pattern creates a grid of pixels, where each pixel can have a color and brightness level.
Characteristics:
- Pixel-based: The screen consists of a grid of pixels, and each pixel can have a distinct color and intensity.
- Continuous Image: Raster scan displays are capable of displaying detailed and complex images, including photographs and videos, because they break the image down into thousands (or millions) of tiny pixels.
- Resolution: The resolution is determined by the number of pixels in the screen, often expressed as width × height (e.g., 1920 × 1080 for full HD).
Examples:
- CRT monitors (older TVs and computer monitors)
- LCD, LED, and OLED displays (modern screens)
- Computer displays, television screens, digital photography, etc.
Advantages:
- Can display full-color images, detailed graphics, and videos.
- Suitable for complex images like photographs, movies, and web pages.
Disadvantages:
- Requires a lot of memory to store the pixel data.
- Image resolution is fixed by the number of pixels on the screen.
2. Vector Scan Display
How It Works: A vector scan display, also known as a calligraphic display, uses an electron beam to directly draw lines between specified points on the screen. Instead of filling in pixels across the screen, the beam moves to specific locations to draw the image by tracing out lines. It doesn't create images by filling pixels; rather, it traces out geometric shapes (such as lines, curves, and polygons) one at a time.
Process: The image is drawn by directly moving the electron beam to the endpoints of each line or curve, creating lines that connect these points. Once a line is drawn, the beam moves to the next point to draw the next line. The process is done sequentially for all the lines that make up the image.
Characteristics:
- Line-based: The display creates an image using only lines and geometric shapes.
- No pixel grid: It doesn't rely on a fixed grid of pixels to create the image, but rather draws lines directly between points.
- Resolution: The resolution depends on the precision of the vector drawing system, not the number of pixels. The image can appear very smooth for simple shapes, but is less suited for complex or highly detailed images.
Examples:
- Early computer graphics (e.g., early oscilloscopes, vector graphics-based arcade games like Asteroids, Spacewar!).
- Some radar systems and scientific equipment that use vector displays to show precise lines or patterns.
Advantages:
- Can display precise lines and curves without the need for a pixel grid.
- More efficient for displaying simple geometric shapes like lines, curves, and text.
- Requires less memory compared to raster displays, as only the endpoints of lines need to be stored.
Disadvantages:
- Not suitable for displaying detailed, continuous-tone images (such as photographs) because it lacks a pixel-based grid.
- More limited in terms of image complexity—vector displays are better for wireframe images and simple graphics, but not for detailed or realistic images.
