1. Join Now

    AVForums.com uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Xbox flicker filter (and why the picture is soft from RGB scart)

Discussion in 'Xbox Forums' started by cybersoga, Mar 14, 2005.

  1. cybersoga

    cybersoga
    Active Member

    Joined:
    Apr 7, 2002
    Messages:
    1,628
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    48
    Location:
    UK
    Ratings:
    +25
    Wondered why the picture from Xbox via RGB scart is softer than most consoles? With interlaced output (NTSC 480i and PAL 576i), the video encoder chip in the xbox heavily filters the picture to reduce flickering, but if you feed it into a progressive display such as a plasma or LCD (with I/P conversion) this just ends up making the picture look soft. The easiest way to get around this is to use the hdtv component video cable and 480p/720p/1080i output, but some games do not support 480p (some pal games only work in 576i). That is why i'd like to be able to disable the flicker filter, and control the level of filtering. Some emulators have this option so I know it can be controlled with software, but i'd like to be able to turn it off with all games. Some people with interlaced televisions would prefer flickering over a soft picture too. Are there any mod's that can set the default flicker filter level? Thanks.
     
  2. Zacabeb

    Zacabeb
    Active Member

    Joined:
    Jan 17, 2002
    Messages:
    474
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    21
    Ratings:
    +9
    There is a lot of stuff going on in the Xbox's video encoder, the flicker filtering is not alone in reducing picture sharpness.

    The first Xboxes used an off-the-shelf video encoder from Conexant, the CX25871, designed for use in the TV output of PC graphics cards. Later, Microsoft replaced it with a compatible but cheaper encoder developed by Focus Enhancements on Microsoft's request, the FS454. Even later they changed to a custom branded one called Xcalibur, whose origin is unknown to the public. Some suggest that the Xcalibur also replaced the venerable Wolfson audio DAC used before. It's as mysterious as the name suggests.

    The Conexant and Focus Enhancements video encoders suffer from a fatal flaw when connected through RGB SCART. Because of the additional filtering needed (not the least the flicker filter), the signal is mercilessly reformatted in preparation, which alone causes a loss of sharpness. And that's not all. What follows is a somewhat technical description of the atrocities commited to the signal.

    >> Tech babble

    First the input is converted from RGB to the YCrCb color space, and the color components Cr and Cb are subsampled to half in the horizontal direction, producing a 4:2:2 signal. From there it is scaled to either 720x480 or 720x576 pixels regardless of the original resolution, with flicker filtering applied in the scaling process itself. The color components are scaled to a 4:2:2 output, so even after scaling they're half the horizontal resolution of luma. There goes a lot of sharpness already.

    And it gets worse. When using RGB SCART, the sync is taken from the composite signal, so the Xbox produces a composite signal alongside RGB. To stay within the bandwidth restrictions required for composite video, the color components must be heavily low-pass filtered, resulting in < 1.5 MHz bandwidth at -3dB. The problem with the Conexant and Focus Enhancements encoders is that they cannot tap the signal before this filtering occurs. As a result, the RGB output is lowered to composite bandwidth.

    << Tech babble

    So in a nutshell, the RGB SCART output of Xboxes with Conexant or Focus Enhancement encoders has color bandwidth as low as the composite output. That sounds outrageous, but alas, it's true. :(

    DVD Video playback bypasses the scaling and flicker filter, but the color bandwidth is still reduced. So much for using those Xboxes as DVD players.

    Newer Xboxes that have the Xcalibur encoder look a whole lot better via RGB SCART than the old ones. Even the Xcalibur, like its abysmal predecessors, appears to scale the image horizontally to 720 pixels, producing a softer image than that of competing consoles. However, it does not appear to subsample the color, and it certainly does not reduce the RGB bandwidth to the same as composite video. The increase in color clarity is shocking. On top of that, the flicker filtering is more tempered and not too obtrusive. But, of course it's still there.

    Whether or not it's possible to make forced entry into the core of the system and changing the flicker filtering for playing games, I don't know. Those modifying their Xboxes for running Linux play around with those settings, but that of course doesn't help when running games.

    I guess an import machine with a HD pack is the only real way to get a truly good quality image out of the Xbox.

    If you have an old Xbox (made before spring 2004), you may gain a bit higher picture quality via RGB SCART simply by upgrading to a new Xbox. That will also get you an Xbox that does not require a 2lbs dongle on its power cord to keep it from exploding...
     
  3. deckard

    deckard
    Standard Member

    Joined:
    Dec 4, 2002
    Messages:
    425
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    16
    Location:
    leicester
    Ratings:
    +0
    Thanks for that Zacabeb, that fit's entirely with my recent experience of connecting a Hi Def pack to an unmodded x-box and outputting interlaced video; it looked like a composite signal! This was confirmed by looking at a colour multiburst signal which showed that the colour bandwidth was just as you've said. I've soft-modded my x-box which has improved things greatly, but it seems a more modern x-box would be best. Think I'll hold out for x-box2 though...
     
  4. cybersoga

    cybersoga
    Active Member

    Joined:
    Apr 7, 2002
    Messages:
    1,628
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    48
    Location:
    UK
    Ratings:
    +25
    Thanks Zac, i've got a recent Xbox with Xcalibur video encoder. I havn't yet got the component cable, waiting for that to turn up from lik-sang. Currently using the official RGB scart cable - Halo 2 looks very soft, Burnout 3 looks ok but not amazing, but if I turn the flicker filter off in the snes emulator suddenly the picture looks great, wish I could do that with all games.

    Pity the xbox doesn't support 576p.
     
  5. blackfly

    blackfly
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
  6. Zacabeb

    Zacabeb
    Active Member

    Joined:
    Jan 17, 2002
    Messages:
    474
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    21
    Ratings:
    +9
    I already knew that the FoxedLink power supply is the culprit, but thanks for the links. I wonder if Mi¢rosoft will be struck by an Act of Gord for putting the blame on the power cord? :D

    Where there's fire, there's smoke... and mirrors.
     

Share This Page

Loading...