PAL Resolutions and Aspect Ratio

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  • #21315
    Jademalo
    Participant

    NTSC resolutions are all fine, but since I’m British and a lot of my childhood consoles are PAL, I feel it could be handled better.
    If I’m making any severe mistakes or incorrect assumptions here then my apologies, but even if my exact numbers are incorrect the general point I’m making shouldn’t be.

    Take for example the Gamecube.
    It outputs 480 content at 640×480. The OSSC samples each line at 720 pixels, including Hblanks. This means when displaying square pixels it results in a 3:2 aspect including Hblanks (720×480), and 4:3 excluding them (640×480).
    It outputs 576 content at 768×576. The OSSC doesn’t change the horizontal sampling resolution for PAL, which when displaying square pixels results in a 5:4 aspect including Hblanks (720×576), and 10:9 excluding them (640×576).

    Since it’s sampling horizontal the same as 480, it means that the visible area for PAL games is 640×576, which is substantially different than the native 768×576 for the correct 4:3 aspect with square pixels.
    This obviously means you’re losing horizontal resolution for PAL, as well as getting a totally incorrect aspect ratio.

    A recommended horizontal sampling rate for digitising PAL TV content is 720 pixels. This however doesn’t assume square pixels, and assumes correction will be applied afterwards in order to properly scale the image. The correct pixel aspect for this is 6:5, however actually getting any devices to properly display 720×576 at 6:5 PAR is a pretty much impossible task.

    Modern TVs set to 4:3 tend to stretch it to ~768×576, which results in a used area of ~683×576.
    Modern TVs set to 16:9 tend to stretch it to ~1024×576, which results in a used area of ~910×576.
    Neither of these resolutions are close to the ideal used area of 768×576, so in no situations can you get a modern display to actually show the OSSC’s PAL output in the correct 4:3 aspect ratio. (Or at least, I’ve been totally unable.)

    In this case (I think), the output resolution for PAL content should be 864×576 / 1728×1152 in order to sample at the same 2:3 aspect as the NTSC resolutions resulting in a 4:3 image when displayed with square pixels on a modern TV.

    I’ve got no idea if this is possible or not since the ideal PAL resolutions are super wonky, but honestly as it is now PAL consoles just don’t display correctly at all.

    #21392
    marqs
    Participant

    Gamecube uses standard DTV timings (858px/525lines@59.94Hz NTSC or 864px/625lines@50.00Hz PAL) in most cases (excluding 240p/288p games, some homebrew like GBI etc.) as far as I know. Those are also the numbers OSSC uses as its default sampling rates for 480i/p or 576i/p modes. The active resolution is more like to vary, but I’d guess 640×480 is most commonly used by GC games. If no PAL optimizations are applied, that results to incorrect letterboxed aspect ratio to begin with, just like with older 50Hz consoles. If PAL-optimized software output 768×576 active area, you’d need to increase H.active from 720 to 768 on OSSC’s 576i preset mode. That assumes your display can handle that resolution correctly.

    #21425
    Thomago
    Participant

    Take for example the Gamecube. It outputs 480 content at 640×480.

    The Gamecube (usually*) renders NTSC content in 640×480, however it puts its render output into a 720×480 frame (see the black bars left and right of the picture?), so sampling 720 pixels is a 100 % correct.
    The Gamecube DOESN’T render PAL content in 768×576 (768×576 output afaik simply isn’t a thing with consoles) – it renders it in 640×576 and puts that into a 720×576 frame. Sampling 720 pixels is correct there as well.** ***

    * There are Gamecube games rendering at less than 640 horizontal pixels.
    ** Also games usually don’t use the full vertical resolution; NTSC games for example commonly render only 448 vertical pixels, the rest is black bars.
    *** You can remove the “Gamecube”; the above considerations are correct for other consoles of that era as well.

    A recommended horizontal sampling rate for digitising PAL TV content is 720 pixels. This however doesn’t assume square pixels, and assumes correction will be applied afterwards in order to properly scale the image.

    This is correct, as there ARE NO SQUARE PIXELS! And yes, you will need your display to “correct” the picture’s aspect ratio afterwards. This is why I searched about a year for a new monitor, as most monitors are unable do that.

    #22397
    deevus
    Participant

    I am also in a PAL region (Australia). Please let me know if I’m hijacking this post Jademalo, and I’ll create a new thread.

    I think that line doubling modes could also be improved for PAL resolutions. None of the modes really work that well in their current state due to the resolutions that PAL consoles output.

    For example, 240p at 3x mode makes a nice 720p output for NTSC consoles, but for PAL at 288p this gives 864p which is not really palatable by many modern displays. I could deal with outputting this as 1080p with some black bars as it’s less than 100px shy of 960p, then zooming using my display. Alternatively my display says it supports 1440×900, which is even closer.

    At the moment I’m using 5x (4x doesn’t work with my TV) in 1080p output mode but I lose a fair bit of the picture which doesn’t work for a lot of games.

    I think in general it would be stellar if the OSSC could have a mode which adjusts to “closest/best available resolution” for modern displays. I understand that this could differ from one display to another. Perhaps you could set which resolutions your display supports via the menu.

    Eg. 3x resolution: 864p
    Display supports 900p? Output as 1440×900

    #22494
    deevus
    Participant

    Any thoughts? How are other PAL users overcoming these problems?

    #22500
    Harrumph
    Participant

    If your display can handle it, just adjust v.active as needed, e.g. 240 to get 720p50 in x3 mode. This is actually already done for x5 mode. See this thread https://videogameperfection.com/forums/topic/tips-tweaks-lx3-lx4-lx5-modes/

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