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Discussion Starter · #1 ·
My question is to what extent you can adjust the thickness of the scanning lines with crt technology. Answer in percentage range like 80-120 percent with 100 percent being the "normal" thickness.


Is the need of line multiplication greater with 8 and 9 inch projectors than with a lesser 7 inch product.


Does anybody have pictures of what scan lines look like on a 8 or 9 inch crt without line multiplication, assume a 480p source.
 

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Originally posted by Ohlson
My question is to what extent you can adjust the thickness of the scanning lines with crt technology. Answer in percentage range like 80-120 percent with 100 percent being the "normal" thickness.
Normal as compared to what?

My XG's resolution is what I consider normal. At 1280X720 on a 80X45" screen, scan structure is visible within about 5 ft of the screen, anything farther back, and the picture looks more like film.

I suppose the answer to this would be, you can adjust the thickness of the scan lines until they disappear.

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Is the need of line multiplication greater with 8 and 9 inch projectors than with a lesser 7 inch product.
I couldn't say the need is any greater, but an 8" can resolve higher resolutions than a 7, and a 9" can resolve even more. I would say, in order to get the best picture out of each class of CRT, finer resolutions/better signal processing should be used as you step up in CRT size.

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Does anybody have pictures of what scan lines look like on a 8 or 9 inch crt without line multiplication, assume a 480p source.
I don't have a picture, but I did hook a 480p DVD player up to my 8" system once...the scan lines were huge, and way to easy to see at viewing distance. All it took was about 10 seconds to realize I didn't want to use 480p on my system.
 

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Originally posted by Ohlson
My question is to what extent you can adjust the thickness of the scanning lines with crt technology. Answer in percentage range like 80-120 percent with 100 percent being the "normal" thickness.


By playing with the focus/CPC/purity magnets on the CRT neck you can make the lines thicker or thinner, but making them thicker is 'incorrect' as you'll get smearing. There's only one correct way to set the thickness really.

Is the need of line multiplication greater with 8 and 9 inch projectors than with a lesser 7 inch product.


This goes hand in hand with your other post - and yes, better projectors usually will require you to scan up higher then lower end models in order to make scan lines disappear.

Does anybody have pictures of what scan lines look like on a 8 or 9 inch crt without line multiplication, assume a 480p source.


Depends on how well set up the PJ is and how big the screen is. 480p is already better then 480i however. If your PC has a large monitor (19" or bigger), one good example is to display a command prompt window as full screen. You'll see how the text is made up of individual scanlines with spaces in between.


Kal
 

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Quote:
Originally posted by Ohlson


Is the need of line multiplication greater with 8 and 9 inch projectors than with a lesser 7 inch product.


Does anybody have pictures of what scan lines look like on a 8 or 9 inch crt without line multiplication, assume a 480p source.
Yes.


I've fed my 9" projector 480p, and the black lines are bigger than the lines of image they separate. With 720p, the scan lines disappear beyond a screen width back or so; although the image doesn't have the same 3D feel as with 960 or 1080p at normal viewing distances (1.2-1.6 screen widths).
 

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Discussion Starter · #5 ·
So you can change the width of a line somewhat , but there is very little margin in thickness change where you retain an optimal picture.


I understand that a badly set up crt can have less visible lines, since good setups are sharper and more defined. Another question related to my first is horizontal scan rate vs optimal number of scanning lines.


An example, let us assume a 7 inch crt. We feed it 1080i and the scan rate is equivalent to 540p so there is no problem there. But with 1080i you have 1080 lines right? If this is supposed to fit within 16:9 of 7 inch tube doesn¨t this lead to overlapping scanning lines and a soft picture?


How do crt owners with 7 inch projectors display hd? With 1080i it most be soft , but that might be preferrable to some. Can one display 1080i as 540p with a crt and is this preferred by some people?
 

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Line width is fixed. The only thing that affects it is astigmation, which we all try to adjust for the smallest beam size, which in turn creates the thinest scanlines. The point of using higher resolutions is to make the CRT draw more of these these so that they are closer together. At some point they will be close enough together that the spaces disappear. That's what we call the "sweet spot". When we achieve this, the resulting image really is "film-like" in that it looks like a complete projected frame rather than a video structure. Going higher than the "sweet spot" just makes the lines overlap and that's just as bad as seeing scanlines.


For 1080i the CRT only has to draw 540 lines at a time so this is easily resolved by nearly all CRT pj's.
 

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Discussion Starter · #7 ·
With 7 inch and 1080i source. Each frame has 1080 lines and each field has only 540 lines. If 1080 lines are not separated with a 7 inch crt and the 540 lines from the first field and the next field overlap, this must lead to a loss of vertical resolution. My point is if the 540 lines in the alternating fields are positioned at the same spot I imagine you lose vertical resolution.
 
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