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barco 808s htpc resolutions and refresh rates.

Discussion in 'Projectors, Screens & Video Processors' started by condor, May 20, 2005.

  1. condor

    condor
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    Hi all I have a ati htpc which is running with powerstrip, my projector is a Barco Graphics 808s, I am running the projector at 1440 at 960 and the image seems quite good. I was wondering what the upper limit of the barco was though and if it can be run at 1600 by 1200 or higher. If this is the case what refresh and scan rate should be used on the vertical and horizon. Thanks to anyone who reads this, even more anyone who answers!.
     
  2. Roland @ B4

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    I doubt very much that you will benift by running high resolutions other than to prove to your friends that your projector can. but to answer your question 16x1200 at 75Hz is possible but the projector will display but not "resolve" the image.
    It will also get hot, make a lot of noise trying to cool it's self. (Oh and it will be much dimmer)
     
  3. Rob.Screene

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    I run a data 808s installed by Roland, off a Radeon 9500 based HTPC.

    I use 1440x960@71.928Hz for ntsc stuff and 1440x864@75Hz for PAL.
    Both 2x multiples of their respective DVD source resolution.

    I agreed with Roland in that these are probably both slightly beyond what the tubes can fully resolve on a 16:9 aspect screen, but I find the scaling much better than running 1280x720.
    i.e at 1280x720 the Radeon's scaling adds artefacts that the 808s then fully resolves, i.e. a CRT picture showing digital type noise!

    This might not be the case with other scaling solutions which might output 1280x720 a bit better.

    regards,
    Rob.
     
  4. crispybig

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    Hi Bob. I run these resolutions too, and fully agree that - irrespective of the PJ being used - it's a good idea to make the scaler's life as easy as possible by using "tidy" multiples of the actual source resolution.

    But to avoid some possible confusion, I'd just point out that 864 is actually 1.5x the source resolution (576) and not 2x.

    Condor doesn't say whether he's using PAL or NTSC with his 1440 x 960 resolution. If it's PAL, then I think 960 is a poor choice, as it's one and two-thirds x 576. Giving a scaler a multiple that's a recurring number can't be good for it!

    Of course, 960 is spot-on for NTSC.
     
  5. Paul D

    Paul D
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    I found running around (1440/720)x720p squeezed to 16.9(AR) to be the sweet spot for my BD808s.
    Lower refresh rates also helped the picture quality, but with slightly more flicker.
    I ran 50hz/59.94 from the scaler, 72(xxx)hz/75 from the HTPC.

    I tried higher resolutions, but found absolutely no reason to do so.
    I understand that multiples of the original source are easier for scaling, but thought "tuning" to your scan lines to be more important.

    At around 720p(and 16.9 AR) i could clearly see scan lines from up close, but not when seated.
    Since the Pj wasn't stressed in anyway(at that resolution/ratio), i found the sharpness/clarity/colours and overall image to be better.

    I also ran a 4.3 AR, and found only then did the higher resolutions come into play.

    Lower refresh rates can also make a big difference, with flicker seeming to be the only downside.(which you do get used too)

    My BD808s had very high hours, but the tubes were in good condition.(slightest of wear to green only)
    If i had put new tubes in, i would probably found completely different results.
    Showing that there is no ideal resolution and refresh rate for any CRT.

    "Suck it and see" comes to mind! ;)
     
  6. cosaw

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    Just a theory qurey to add to do with horizontal resolution. I understand about scaling to multiples and all.

    Theoretically is there any point upscaling the horizontal resolution beyond the horizontal resolution of the source material seeing that the pj draws continuous horizontal lines anyway? Do you gain anything or does it have to be done to maintain the aspect ratio and not need a massive anamorphic vertical squeeze at the pj end?

    For instance take the resolution of dvd 720x576.

    For sake of argument, and to make the maths simple, say your pj could quite happily resolve 576 x 2 = 1152 lines. In upscaling to this you would also (normally) naturally double the horizontal res as well so you get to: 1152 x 1440.

    For 16:9 anamorphic source data you'd then anamorphically vertically squeeze via the pj so apect looks correct. Presumably dvd pixels are anamorphic? Does this mean that you can change the horizontal resolution (via scaling) and at the same time not alter the physical aspect ration of the data (before the anamorphic squeeze), i.e. you'd only have to squeeze the image by the same amount no matter what the horizontal resolution.

    So before anamorphic squeeze will 1152x720 always look (if you could see it on a computer monitor before sent to pj and anamorphically squozen) half the width of 1152x1440. Or with the dvd being anamorphic (and presumably the pixel data) would they both appear to be the same physical aspect ratio.

    If this was the case and increasing horizontal resolution does nothing as far as the pj is concerned then you would theoretically never need to upscale horizontal resolution. Theoretically you could run 720 x (576 x 1), 720 x (576 x 1.5), 720 x (576 x 2), 720 x (576 x 3) etc etc.

    Aybody have any thoughts or answers on this??

    Simon
     
  7. crispybig

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    Agreed - it's a best compromise. No-one can argue with "suck it and see"!

    What I meant was once you have found a vertical scan rate that looks good on the screen, there's something to be said for adjusting it to the nearest "sensible" ratio for the scaler.

    For instance, rather than 960 for PAL, I would try 936 which is one and five-eighths x 576. The scaler works in binary, and eighths is a "power of two" number. This will better match the algorithms in the scaler's software. There is no doubt that given a scaling factor that involves a recurring number (e.g. as with 960) the scaler will have to do some rounding / approximation at some point. This all takes time for the scaler to work out, and so must rob it of some processing bandwidth. It also means that each pixel has to be more of an approximation than it needs to be.

    Think of it as the scaler having a "sweet spot" as well as the PJ. Actually a number of them, some sweeter than others!
     
  8. crispybig

    crispybig
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    Simon - very interesting point! Now you've prompted me to think about it, what advantage is there in running 1440 over 720 horizontal?

    I think your anamorphic discussion is a red herring, as it's all to do with the vertical domain, and has no effect on the "pixels" within a single horizontal line.

    With 1440 I guess the scaler just doubles the pixels. Once it's gone analogue, there is no difference between two small 1440 white pixels next to each other and one larger 720 pixel - is there?

    So having to do the pixel doubling is just wasting scaler processor bandwidth for no gain. Ummm - I think I'll try 720 instead of 1440 and see if there's any perceivable difference.
     
  9. cosaw

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    Hi Chris - Not sure what you mean about anamorphic discussion being a "red herring". However I can see you understand what I'm talking about. It seems daft doesn't it to upscale horizontally? As you say it takes extra processing power and for what gain?

    I'd be interested to know what you find and if it is doable without having to squeeze the image vertically twice as much. If it works then everyone could run like this and save more of their processing power for vertical scaling.
     
  10. crispybig

    crispybig
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    Simon - what I meant is I can change my H resolution from 1440 to 720 and there will be NO change is picture width. It will NOT suddenly half in size. The aspect ratio will NOT change. Anamorphic or non-anamorphic, 16:9 or 4:3.

    Horizontal resolution has nothing to do with picture width. Just like vertical resolution has nothing to do picture height. If you switch source from 460P to 920P (say) the picture doesn't suddenly double in height. There are just twice as many lines in the same height.

    So going from 720 horizontal to 1440 just creates twice as many pixels in the same width. It's just that you can't actually see the pixels, whereas you can see the vertical lines (at least in principle - they can disappear in practice, of course).

    I won't have chance to experiment with the PJ for a while. The current project is fitting a wired burglar alarm to the house. Having great fun (NOT) invisibly threading the wires throughout the house (under floorboards, behind the plasterboard, etc., etc.)

    Checking here during coffee breaks for light relief! :D
     
  11. Yorcci

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    I'm using only 576p @ 75 Hz with my BD 808s and I can't see scanlines from viewing position. Screen width 2 meters, viewing distance 3 - 3.5 meters. With 480p @ 59.94 Hz I do see scanlines occasionally, but not all the time. If I go a little closer, say 1 and a half meters from screen, the scanlines are very visible, although with 576p very thin.

    I've been wondering, if there is something terribly wrong with my setup. I have adjusted the astig magnets and electrical focus as close to perfection as 'humanly possible'. I would have expected to see scanlines with 576p for I had to use 720p with my previous BG 800. This was due to some 'vertical drifting of scanlines' when using 576p. But that's another story. I won't bore you with it.

    Barco has about 4000 hours and some wear on green tube, but red and blue are as good as new, at least judged by bare eyes. :rolleyes:
     
  12. cosaw

    cosaw
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    Chris - thanks for clearing that one up for me. In that case 720 horizontally for dvd should be perfectly adequate for anyone and upsacaling in this direction will probably add nothing. I too have got some underfloorboard work to do and its no fun you're right :thumbsdow

    Yorcci - its probably just to do with your viewing distance. Even if you can't see the scanlines from where you sit perhaps if you uped the vertical res to fill the gaps you'd get more light back from your screen - a brighter picture. Theory seems sound not sure about the practice though.
     
  13. christoph

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    hi crt-lovers

    i own a bg808s driven by a radeon htpc and i use 1920x960@47,952 hz for ntsc and 1920x864@50.000 hz for pal dvds.

    by using high horizontal resolutions you can avoid aliases by upsampling without even increase the scanrate.

    to achieve a real crisp picture you should try to tackle down the scanrate by chosing a low refresh rate like the above mentioned ones. and it flickers less than in a real cinema ;)

    maybe you should try the low refresh rates, the picture wins a lot of crispness :smashin:
     
  14. cosaw

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    Hi Christoph,

    Some interesting points but I'm a little confused perhaps you could clarify them furhter.

    I didn't know scan rate had any bearing over aliasing at all. How does this work?

    Also I thought as long as you extract the maximum resolution (in my case pal dvd is of main interest at 720x576) then you would get rid of all aliasing anyway. This is the way I got rid of all aliasing on my pj. Is this correct or can aliasing still be reintroduced?

    You seem to be suggesting that if you don't upscale by the same factor both horizontally and vertically that aliasing will be reintroduced even if you are running at a higher resolution than the source material. Is this actually the case in your experience? I don't know - can't try it on my little SD-187 tubes - I'm probably maxing out at 720x576 but thats all I need at the moment to avoid aliasing on pal dvd. The image is probably on the softer side but I prefer this than alaiasing any day.

    Lowering refresh rate to give more crispness - I've heard this before. Will have to try this - I'm currently running at 75Hz have to try 50 to see if that gives me more crispness. Not to bothered about flicker as I'm not as sensitive to it as many people. However does it affect brightness in any way - are you getting less brightness at the lower refreshes?
     
  15. christoph

    christoph
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    the scanrate doesn't affect aliases at all, a low scanrate can give you a crisp picture with depth.

    scaling can avoid aliases when its done in a sensible way. native resolution multiplied by a even number within the possibilities of your crt. my bg808s has its sweetspot vertically round 900 to 1000 lines. horicontally you can chose 40 mio pixels, as it DOESN'T affect the scan rate, but its not reasonable to do so. 1440 or 1920 seems to be best. you can reduce aliases just by increase the scaling but you can do it better by choosing "good" resolutions, that can be scaled by the graphics card without bringing in new artifacts due to uneven factors.i'm sorry as i can't explain it properly as i don't speak english too well and also don't understand this completely, but if you understand a little german then you should read through the link below from a german forum.

    http://62.206.102.34/forums/showthread.php?t=18916&highlight=aufl%F6sung

    and this is the homepage from the author of the link above (in english):

    http://www.videophile.info/

    its not necessary to have the same factor for horicontal and vertical scaling as you can scale as much as you like horicontally without increasing the scanrate but you should find the sweet spot of you crt vertically, so different factor are almost an obligation...

    a few examples for reasonable resolutions:

    Low-end:
    NTSC 1440x480@48
    PAL 1440x576@50

    Mid-Class:
    NTSC 1440x720@48
    PAL 1440x864@50

    Upper-Class:
    NTSC 1920x960@48
    PAL 1920x1152@50
     
  16. Paul D

    Paul D
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    I mentioned the "720"H Res in my post.

    The HTPC seemed sweet at 1440H, but the scaler just ran at 720H.
    I would have run at 720H(x720V) from the HTPC but didn't know how to do it at the time.

    I was surprised on how the overall picture can change from different resolutions and refresh rates.

    Hi-def means 1280Hx720V (p) and 1080i also needs to be considered, but these don't need any scaling :thumbsup:

    I think Roland would be the best person to advise what looks best on what!
    (Rumour has it that he's seen one or two CRTs)
     
  17. cosaw

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    Christoph thanks for expanding on that - I think I get the gist of what you're saying and will have a look at your links and perhaps run them through a translator.

    Yes Paul you did - sorry overlooked that when making my first post. Yep Roland is the man - I'm quite happy with how my pic looks and there is no aliasing that I can see. Just like to understand the theory a bit. Seems from Rolands post that some people try and get too much out of their machine and end up running past optimum.
     
  18. Yorcci

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    The reason I'm using such low resolution is to keep my Barco as cool as possible. It can be a little noisy when warming up properly :(

    The light output is not my concern, this bad boy can deliver enough light even with moderate contrast adjustment :cool: I was just surprised that I couldn't see the scanlines. I thought I definitely should see them with this PJ at such resolutions.

    And I just realized that this thread was concerning htpc resolutions. I'm using external scaler. Should also learn how to read. :suicide:
     
  19. crteaman

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    As paul suggests, 1440x720 is superb on an 808s, in fact on a unit with A1 tubes 1440x960 is just possible too.
    Paul correctly points out the strange inter-action between different units and their ability to clamp the signal correctly, often due to the way their controller interprets timing specs ie front porch and back porch with a certain amount of effort many of the crt units out there can be made to lose raster ringing as well.

    Paul, hope Gav'a tear gas didnt curtail your drive home :rotfl:


    james
     
  20. Paul D

    Paul D
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    Hi James!
    I went home in a daze, but not because of the BBQ smoke!
    Both me an Chris just really enjoyed the day.(Thank you!)

    Running at 720p enabled me to get rid of the Raster Ringing, and allowed the whole image to "tighten" up.
    960p was possible, but i thought it too soft when running 16.9.(sharp with 4.3 though)

    I did try some interlaced resolutions, but they really didn't sit too well with me.

    I just took the view that DVD/SKY is lower res anyway, and Hi-Def can look great at 720p.

    9" CRTs would need higher resolutions just to keep the scan lines in check!
    (1080p hmmmm!)
     
  21. crteaman

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    Yeah brother.

    james


    he he, think I have found a new draw for the next...................(seriously)
     
  22. Yorcci

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    Ok, found the reason why I couldn't see scanlines with 576p. The focus unit on the green crt was installed a little bit too 'behind' on the tube neck and wasn't giving the best focus. After I moved it tightly in contact to the deflection yoke, the scanlines became visible. Which means I had to change into 720p.
     
  23. Roland @ B4

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    :eek: :eek: :eek:

    Are you sure you should do that
     
  24. Yorcci

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    Yes, I am. :hiya:

    You might get confused with my English, but first I did check also the red and blue, and they had the focus unit connected to that ugly wodge in front of them and they both had better focus than the green one. It's also mentioned in a tube replacement guide from Barco to move the focus unit to get the best focus. I think that ugly wodge was the deflection coil. Hope you understand what I mean...

    There's also a downside (as always): now I can see those damn scanlines every now and then even with 720p :devil:
     

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