Scaling on high vs low pixel density displays

Discussion in 'General TV Discussions Forum' started by Renoir, Dec 31, 2006.

  1. Renoir

    Renoir
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    I have recently been thinking a lot about watching high def content on laptops and so decided to once again read the excellent post by NicolasB on Optimum screen size/viewing distance which can be found at http://www.avforums.com/forums/showthread.php?t=312431

    I downloaded the excel spreadsheet and typed in a viewing distance of 2 feet and found that a 15.4" display would be ideal for watching 1080p content which just so happens to be a common laptop display size. It's quite strange at first to think that you'll actually resolve more detail sitting close to a laptop than when sitting 8-10 feet away from a 42" screen but there you go.

    Now my question is not whether I'll notice the resolution of high def dvd's etc on a laptop (seems pretty clear from the above thread that I would) but rather what effect pixel density has on the ability to scale SD content. Just from subjective experience I have found that normal dvd's tend to look a lot better on high density computer screens than when blown up on a large size but low density screens.

    So was wandering if anyone had any thoughts or info on whether it's easier to scale SD on high or low density displays?
     
  2. sinizterguy

    sinizterguy
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    High density (I assume you mean higher resolution screens) would result in smoother lines and less jaggies. Also PCs are inherently good at scaling, so I would say that it would look better.

    It would be "harder" to scale to higher resolution displays as they need more data to look the same. But then PCs do this without any problem.

    I think you would get a very solid vibrant and punchy picture on a PC screen compared to a large screen TV.
     
  3. Pecker

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    NB's posts at the thread are superb and well researched, but the concept is limited in its own way - many (though not all) will see this as a fundamentally flawed way of choosing seating distance.

    I'm not here to say Nic is 'wrong' - it's up to each individual to decide on how to decide where to sit - but ultimately I feel the alternate way of calculating seating distance is probably more applicable to most people.

    NB's thread implies that seating distance should be chosen by the resolution of the displayed image - deciding how close to sit based on how much detail you can see.

    I feel that the whole concept of home cinema is to replicate the 'real' cinema experience and see the picture as the director intended.

    According to THX, the recommended viewing distance is 36 degrees, which gives a seating distance of between 1.5 and 1.6 screen widths. That's for a cinemascope screen, which in the cinema is fixed height/variable width.

    In the home our screens are usually the opposite. They're almost always fixed width and variable height. So, if most of your viewing is 1.85:1 & 1.77:1, then the recommended THX viewing distance becomes a little further away than this, unless it's practicle in your home cinema to change seating distance dependent on the screen ratio.

    It's important to note that, if you do this, you might not see as much detail as if you set your seating distance according to resolution. But for me, setting my seating distance this way is putting the cart before the horse. I want my home cinema to be as much like the real thing as possible.

    I don't choose my seat at the cinema based on how much detail I'll be able to see. If I sit in the middle of the cinema it's probable that I don't see as much detail as if I sat at the front. No, I choose seating distance by where it's comfortable to see the image the director shot. So, for me, NB's concept is flawed.

    Nonetheless, each to their own.

    Steve W
     
  4. arfster

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    Fair points. The above is one of the reasons why 1080p was adopted - it provides approx 33 degrees (or something close) viewing angle at the ideal seating position as calculated from NB-like methods.

    Also, another element is in the picture "character" (can't think of a better word) of each technology. People have been using 720p or even SD projectors at ultra close distances for ages, but if you try sit at a comparable screen-width based distance from a LCD screen it looks horrible. Something to do with fill factor maybe?
     
  5. Stephen Neal

    Stephen Neal
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    Hate to muddy the waters - but haven't seem much discussion of the Lechner distance in this thread.

    Lots of discussions centre around optimal viewing distances varying with screen height. However in many home viewing environments the viewing distance often ISN'T optimal - and in many cases as people change their TVs (usually increasing their size) they often still sit at the same viewing distance and don't move their sofa etc. when they change TVs (think of people who have moved, in the same living room, from a 21" 4:3 set to a 28" 16:9 set to a 37" Plasma over the last 10 years or so - which isn't unusual, but many people don't re-arrange their rooms to change their viewing distance at the same time).

    In different countries this varies a bit - but there is a very strong average, called the Lechner distance - and as screen size increases resolution has to increase to ensure you don't resolve scan lines and pixels at the Lechner distance.

    In the US the average screen size for a TV sold, viewed at the Lechner distance, started to benefit from HD broadcasts (i.e. at the Lechner distance your eyes would resolve the benefit of HD over SD - and not see the HD structure) in around 2001 I believe. (This was a function of increasing screen size in the US market - driven by plasma and LCD flat panels, and DLP/LCD rear pros)
     
  6. Renoir

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    Thanks for the replies guys, you have brought up some very interesting points about choosing your viewing distance but that wasn't really what my question was about. The first part of my post was merely outlining my being somewhat surprised by a 15.4" laptop being able to fully benefit from 1080p resolution from a distance of 2 feet as per NB's posts. It was merely meant as an observation.

    My questions actually related to the ability to scale sd content on high pixel density vs low pixel density displays. To be clear I'm not talking about resolution per se but rather resolution per given area e.g. a 720p laptop screen has a higher density display relative to a 720p 32" HDTV. I guess the way I should put the question is thus: Assume just for the minute that the general scaling quality is equal (which sinizterguy rightly points out is often not the case). When watching an SD DVD on either a 1080p laptop (approx) or a 50" 1080p lcd, which would have a better scaled up image? ISTR reading somewhere that it's generally easier to scale for a higher density display all else being equal but thought I'd get some info from you guys. I hope that's clearer now if not let me know and I'll try again :smashin: Oh and Happy New Year to you all :clap:
     
  7. waycool

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    Renoir, upon upconversion would not any pixel to pixel approximations be just as evident in any pixel density if you were able to view it with a "microscope" so that these flaws might contribute equally to any pixel density and display sizes, and thus might one conclude that viewing distance is still the best determinant for picture quality?
     
  8. Renoir

    Renoir
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    Thanks for the reply waycool.

    Correct me if I'm misunderstanding you but are you saying that along as the viewing distance relative to the screen size/resolution is equal between any 2 differing pixel density screens then the image will be comparable?

    For example using nicolasb's calculator the following scenarios would offer comparable image quality assuming equal scaling:

    15.4inch at 2 feet
    50inch at 6.5 feet

    I had a private message exchange with nicolasb on the subject and he says that the above is indeed the case and that pixel density as a "standalone variable" is not important.

    I guess my initial experience with seeing sd being scaled up better on my laptop vs on hdtvs made me think it had something to do with the pixel density whereas it's becoming clear that it's the better quality scaling on computers in general that caused the better perceived quality on the laptop.
     

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