New to the forums? Click here to read the "How To" Guide.

Developer? Click here to go to the Developer Forums.

HDMI cable vs DVI, and black levels... makes a difference?

captaintripscaptaintrips Posts: 313
Art3mis
edited August 2013 in General
Reading around, it appears using a straight DVI cable from the rift to your gpu instead of HDMI provides darker black levels, where as using HDMI (or the HDMI to DVI adapter included with the rift) produces lighter/gray black levels.
And this is more apparent if your downsampling from higher resloutions.

I'm assuming the rift requires a duallink DVI cable, and not just any standard one, based on the pinout on the DVI port on the back of the controller, but before I invest into such... is this correct? any merit to these rumors?

Comments

  • geekmastergeekmaster Posts: 2,866
    Nexus 6
    edited November 2016
    HDMI depends on video card settings. There is a 0-255 range, and a 16-235 range. It makes a huge difference in black levels. Some video drivers switch modes depending on video content, such as movies.

    You can read more about it here:
    viewtopic.php?f=34&t=1130&p=12637#p12637
    viewtopic.php?f=26&t=103&p=14892#p14892
    https://forums.geforce.com/default/topic/515921/hdmi-output-video-levels-16-235-vs-pc-levels-0-255-/
    http://en.wikipedia.org/wiki/Rec._709
  • captaintripscaptaintrips Posts: 313
    Art3mis
    thanks geekmaster!

    Now the the next question... do I need a dualink dvi cable for the rift, or will a standard dvi cable work?
  • geekmastergeekmaster Posts: 2,866
    Nexus 6
    edited July 2013
    thanks geekmaster!

    Now the the next question... do I need a dualink dvi cable for the rift, or will a standard dvi cable work?
    What? Is your Google-Fu broken or something? :lol: It gets better with practice, you know... ;)

    Standard Single-Link DVI is fine.
    ... A single-link DVI connection consists of four TMDS links; each link transmits data from the source to the device over 1 twisted wire pair. ... Each TMDS link carries binary data at ten times the pixel clock reference frequency, for a maximum data rate of 1.65 Gbit/s × 3 data pairs for single-link DVI. ... For practical purposes, this allows a maximum screen resolution at 60 Hz, for widescreen 16:10 ratio of 2,098 × 1,311 or, for 4:3 ratio of 1,915 × 1,436 pixels, or for 5:4 ratio of 1,854 × 1,483 pixels. ... Cable lengths up to 15 m (50 ft) can be used with displays at resolutions up to 1,280 × 1,024. For longer distances, the use of a DVI booster is recommended to mitigate signal degradation.
    The Rift DK is 1280x800 @ 76Hz maximum refresh rate, and certainly well within the maximum data rate limits for Single-Link DVI as shown above. And just for that little bit of extra special proof (I like to be thorough, after all), take a quick look at your Rift DVI cable or DVI/HDMI adapter and compare it to this chart:
    181px-DVI_Connector_Types.svg.png
    You will see that the Rift is missing extra pins needed for Dual-Link DVI. So yes, Single-Link DVI is just fine. Of course, you CAN use a Dual-Link DVI cable instead, if you want to just for "fun". ;)

    Notice that at the resolution used by the Rift DK, you can use a DVI cable up to 50-feet long without a DVI booster! :D
  • MorbidDonkeyMorbidDonkey Posts: 284
    Hiro Protagonist
    geekmaster wrote:
    What? Is your Google-Fu broken or something? :lol: It gets better with practice, you know... ;)

    Now that this is answered and on the internet you will now be immortalized for answering this question! You are now ONE with the Google. Mind....Blown! :shock:
    -: MorbidDonkey :-
    ===================================
    LOGISTICS - Oculus Prototype 1
  • captaintripscaptaintrips Posts: 313
    Art3mis
    Yep, Geekmaster just made history. Anytime someone thus forth googles said question, they now have a immediate first link page with an answer.


    With that said, it will still not stop the inevitable 30+ further threads questioning the same damn thing.
  • philipcuphilipcu Posts: 3
    NerveGear
    If you are using NVidia drivers - I've recently found a way to get the colour to be much richer and the blacks a lot more black on an HDMI cable.
    In the drivers select: Display > Adjust desktop color settings. Then select "Rift DK", scroll down to the bottom where it says "Digital color format" and select "YCbCr444"
  • KBKKBK Posts: 983
    Art3mis
    philipcu wrote:
    If you are using NVidia drivers - I've recently found a way to get the colour to be much richer and the blacks a lot more black on an HDMI cable.
    In the drivers select: Display > Adjust desktop color settings. Then select "Rift DK", scroll down to the bottom where it says "Digital color format" and select "YCbCr444"


    HDMI is a consumer interface.

    Film has a black level issue. In the video and CRT display industry, at the pro level...they have two settings for black level.

    0 IRE and 0.7 IRE. 0.7 IRE is the elevated black level. 0 IRE is the true black level.

    Some Blu-rays and DVD's have elevated black levels, some do not. Your given DVD and bluray player has as an adjustment in the settings, for this exact issue.

    It should be on the top menu, as the problem is variable from disc to disc, film to film. It is a true standard, it is just that it has two settings.

    Since this is all computer based with the Rift, the default setting of the HDMI out on the given GPU, which appears to be an elevated black level, this seems to be the creation of an issue for the rift's scaling hardware (outboard LVDS box). The default is the elevated level, a consumer standard application.

    444 is pro level output, which is full scale, maximum delineation and ranging, editing level, etc..which defaults to 0IRE black level.
    Intelligence... is not inherent - it is a point in understanding. Q: When does a fire become self sustaining?
  • feysalfeysal Posts: 1
    NerveGear
    You can read more about dvi vs hdmi at Techie Lens.
  • AntDX3162AntDX3162 Posts: 839
    Trinity
    I think the biggest difference would be if the panel is HDR or not but I haven't really seen an HDR monitor in real-life.  The difference looks a lot in terms of color depth and brightness.  Those 4k 21:9 HDR panels coming out for like $5k each.
    facebook.com/AntDX316
  • flexy123flexy123 Posts: 792
    3Jane
    It's not "the cable" creating the incorrect (limited) output range, it's the Nvidia drivers assuming that everything connected to HDMI is a TV instead of a digital display. There are several workarounds for this which have been talked about multiple times already so I won't get into detail there. The DVI adapter/cable merely does away with this issue since the display is not connected to HDMI in the first place with it, so it forces the drivers to always output 0-255 "PC level" output range.

Sign In or Register to comment.