Even in the early days of video projection it became clear that standard video was going to need some work to bring the quality and resolution up to that needed for large screen display.

CRT projectors rarely have video  processors built in and rely on external boxes to improve the image. what these boxes are doing is artificially increasing the number of lines from the video source.

In the simplest form just doubling the lines to the more complicated boxes that re-digitise the source and scale the image up hence Scaller"

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