Shadow masking in computer graphics (specifically in older CRT displays) is a technique used to ensure that the electron beams emitted by the electron gun hit only the intended phosphor dots on the screen, creating the correct color.
Here's a breakdown:
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The Problem: CRT (Cathode Ray Tube) displays use electron beams to excite phosphors that glow red, green, or blue. Without a mechanism to direct the beams precisely, they could strike the wrong color phosphors, leading to distorted colors and a blurry image.
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The Solution: Shadow Masking: The shadow mask is a thin metal plate with tiny holes etched into it. It's positioned between the electron gun(s) and the phosphor-coated screen.
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How it Works:
- Electron Beams: The electron gun emits electron beams.
- Masking: The shadow mask "masks" or blocks electrons that are not properly aligned. Only electrons that pass through the holes in the mask can reach the screen.
- Precision: The holes are precisely aligned with the phosphor dots. This ensures that each electron beam strikes only the correctly colored phosphor dots (e.g., the red beam hits only the red phosphor dots).
- Sharp Image: By blocking stray electrons, the shadow mask effectively creates a smaller, more rounded point of impact, leading to a sharper and clearer image.
In essence, the shadow mask acts like a stencil, allowing only the correctly aimed electron beams to reach their corresponding phosphor dots. It absorbs the misdirected electrons, preventing them from interfering with the image. This is crucial for creating accurate and vibrant colors on a CRT display.
