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Discussion Starter · #1 ·
When a scaler triples or quadruples the number of horizontal lines (e.g. 720 or 960) of an NTSC source such as DVD, does the number of vertical lines remain the same as on the source material (e.g. 250 on VHS and 720 on DVD), or is this increased as well. Does this depend on the scaler (Dwin Transcanner vs Faroudja or other)?
 

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It depends on the scaler. All de-interlacers and scalers have a "pixel width". You can think of this as the "number of vertical lines, or dots, across" in terms of the output format. A scaler with a choice of scalings might have a different pixel width for each choice although the pixel width stays the same when you change inputs from, say, VHS to DVD.


The pixel width governs the number of vertical lines across relative to the source material that is preserved. The number of reproduced upright lines or pixels across is never more than the lesser of that of the incoming source material and the pixel width of the scaler.


Oversampling means that the pixel width of the scaler is greater than the resolution of the source. A scaler with pixel width of 720 will reproduce VHS tape (320 max pixels across) with no problem and will reproduce laser disk (560 max pixels across) with almost no degradation. Many videophiles say they can detect some softening of DVD video when the external de-interlacer or scaler connected via the usual analog component video cable has the same 720 pixel width as DVD. The amount is subjective but it takes 10% to 30% oversampling to avoid this softening of analog input.


Video hints:
http://members.aol.com/ajaynejr/video.htm
 

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Discussion Starter · #3 ·
Is HTPC generally preferable to a standalone scaler with a pixel width of 720 in that it can easily produce double the pixels of DVD (1440) via interpolation? This is assuming that the display device can handle that resolution.
 

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You have to do the research to be sure that the scaler or HTPC software actually takes advantage of a greater pixel width.


The purpose of the pixel width greater than 720 is to allow picture details to be aligned on a finer pitch than increments of 1/720'th the screen width. A CRT based TV does not need added resolution for this since picture details themselves don't have to be narrower than 1/720'th the screen width.


Re-aligning picture details away from the 1/720'th grid implied by the original DVD material is useful for constructing the intervening scan lines during upscaling and thus making diagonals smoother. Some scalers also try to re-align picture details on the original scan lines. All such re-alignment is interpolation which by definition is guesswork as to whether the original source was or was not that way.


If a fixed pixel display such as an LCD screen does not have its own pixels as fine as the scaler's pixel width, picture details will be re-realigned and this time probably quite arbitrarily.


Some stand alone scalers (such as a Lumagen Vision) also have a wider pixel width for the scaling portion of their processing.
 
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