A few scanning tips

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Does dot pitch determine video resolution?

No, we hear that too, but image resolution has nothing to do with the monitor's .26 or .28 mm dot pitch. Dot Pitch is the spacing of the monitors red, green, blue phosphor dots on the physical screen. Smaller dot pitch is better, it can improve the sharpness of what you see, but it is fixed for the monitor and is not related to the specific image at all, nor to the specific screen resolution either. The dot pitch never varies for the one monitor, regardless of screen resolution setting. It's more like a filter that we view the image through, which purifies the image we see.

The image pixels are instead created in the video board's memory, to match a previously specified screen size like 800x600. The video board has enough memory bytes to store the three Red, Green, and Blue color values for every individual pixel in the 800x600 image. 800x600x3 = 1.44 million bytes, which is why 2 meg video boards were popular. But 1024x768x3 is 2.36 million bytes, which is why 2 meg boards can't do 24 bit color at 1024x768. Anyway, this memory on the board IS the image, or is at least the image data. When software desires to draw a different image, it is written into this memory on the video board.

The video board uses a RAMDAC chip (interface between RAM and the Digital-to-Analog Converters) to access that image memory quickly to create continuous analog RGB sweep signals that the monitor can display. The glass monitor image itself is NOT digital, and so actually, it no longer contains pixels (but LCD screens are digital, however some are driven from the same analog video board for compatibility). The glass tube's three RGB analog swept beams of electrons are modulated with the image intensity patterns. The dot pitch screen mostly blocks the beams, but it has holes aligned for the purpose of allowing only the properly timed electrons to hit the screen, the red beam can only hit red phosphor cells (otherwise it cannot work). Basically, the dot pitch screen keeps out interference for purity. Dot pitch is related to the geometry of the electron gun and the screen's phosphor cells. It does represent a finite upper limit of detail that can be realized from this monitor, smaller dot pitch is better, but it is totally unrelated to the resolution of the current image or current screen size. You can change the screen resolution (size in pixels) without buying a new monitor for example.

This analog implementation within the monitor, while real, is not actually detrimental to our notion of visualizing that the image is composed of pixels, so we tend to still do that because it remains convenient. The analog image is certainly a representation of the original digital pixels.


Copyright © 1997-2010 by Wayne Fulton - All rights are reserved.


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