Raster and Random Scan displays - video display devices | CGV | SNS INSTITUTIONS
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Raster-Scan Displays
Raster-scan displays render images by sweeping across the screen one row (scan line) at a time, much like a TV set.
Definition & Principle: In a raster-scan system, an electron beam (in CRTs) or pixel driver (in flat-panels) moves sequentially from the top left to the bottom right, illuminating pixels based on values stored in a frame buffer .
Frame Buffer: A dedicated memory area—called the refresh buffer or frame buffer—holds intensity (and color) values for every pixel. During each refresh cycle, the beam reads this memory to reproduce the image .
Advantages:
Well suited for complex, shaded, and filled scenes because every pixel is addressable .
Supports interlacing to reduce flicker (alternate-line refresh) and high resolutions .
Disadvantages:
Requires large memory proportional to resolution (width × height) .
Less efficient for simple line drawings; beam spends time scanning blank areas .
Random-Scan (Vector-Scan) Displays
Random-scan displays, also called vector or stroke-writing devices, draw images by directly tracing each graphical primitive.
Definition & Principle: The electron beam is steered only along desired lines and curves, moving from one endpoint to another and blanking while in transit, rather than scanning the whole screen .
Display File: Instead of a pixel frame buffer, a refresh display file stores a list of line-drawing commands (start/end coordinates, intensity). The beam controller reads and redraws these primitives each refresh .
Advantages:
Infinite geometric resolution for lines and curves—no dot-pitch limitation .
Memory efficient for line-art or wireframe CAD models, since only primitives are stored .
Disadvantages:
Poor at rendering filled areas or complex scenes—each shape must be retraced .
Refresh rate falls as the number of primitives grows, leading to flicker if overloaded .
Видео Raster and Random Scan displays - video display devices | CGV | SNS INSTITUTIONS канала A Indhuja
Raster-Scan Displays
Raster-scan displays render images by sweeping across the screen one row (scan line) at a time, much like a TV set.
Definition & Principle: In a raster-scan system, an electron beam (in CRTs) or pixel driver (in flat-panels) moves sequentially from the top left to the bottom right, illuminating pixels based on values stored in a frame buffer .
Frame Buffer: A dedicated memory area—called the refresh buffer or frame buffer—holds intensity (and color) values for every pixel. During each refresh cycle, the beam reads this memory to reproduce the image .
Advantages:
Well suited for complex, shaded, and filled scenes because every pixel is addressable .
Supports interlacing to reduce flicker (alternate-line refresh) and high resolutions .
Disadvantages:
Requires large memory proportional to resolution (width × height) .
Less efficient for simple line drawings; beam spends time scanning blank areas .
Random-Scan (Vector-Scan) Displays
Random-scan displays, also called vector or stroke-writing devices, draw images by directly tracing each graphical primitive.
Definition & Principle: The electron beam is steered only along desired lines and curves, moving from one endpoint to another and blanking while in transit, rather than scanning the whole screen .
Display File: Instead of a pixel frame buffer, a refresh display file stores a list of line-drawing commands (start/end coordinates, intensity). The beam controller reads and redraws these primitives each refresh .
Advantages:
Infinite geometric resolution for lines and curves—no dot-pitch limitation .
Memory efficient for line-art or wireframe CAD models, since only primitives are stored .
Disadvantages:
Poor at rendering filled areas or complex scenes—each shape must be retraced .
Refresh rate falls as the number of primitives grows, leading to flicker if overloaded .
Видео Raster and Random Scan displays - video display devices | CGV | SNS INSTITUTIONS канала A Indhuja
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