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Displays YCbCr420 vs YCbCr444 colour formats on 4K TVs as monitors

Discussion in 'Tech Support' started by 3lusive, 18 Feb 2023.

  1. 3lusive

    3lusive Minimodder

    5 Feb 2011
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    I've recently purchased another AU7100 65" 4K VA panel @ 60hz for dual monitor/gaming setup.

    However, my graphics card, an old Powercolor RX550, only permits 2x 4K @ 60hz connections by using DP and HDMI. I do not game on the PC, so this is about how it looks within Windows (gaming on Xbox is fine).

    Obviously, the TV's do not accept DP, therefore I'm using a 4K @ 60hz DP to HDMI cable (which works perfectly fine for my non-pc gaming needs, although I will be upgrading the GFX card shortly when prices stabilise).

    However, I have now noticed that the HDMI connection (the one not using the DP to HDMI converter cable), has ever so slightly better overall contrast (swapping the cables around confirms this). It's very slight, but it's there; the picture quality is just better. I run the TV's on Samsung Entertainment mode on desktop (and Dynamic in gaming), as these tend to give the best black depth and contrast. I went into Windows advanced settings and it displays:
    • HDMI connected TV: YCbCr444, 8-bit, SDR, 4K @ 60hz
    • DP to HDMI connected TV: YCbCr420, 8-bit, SDR, 4K @ 60hz (looks slightly worse contrast)
    I'm aware this has to do with the chroma subsampling, but are these the correct colour formats, and is this normal or is something wrong (could I change the DP-HDMI colour format to get a better image, without having to change cable or buy a new GPU)? Do I basically need a GPU that allows multiple HDMI connections if I was to correct this (it's not major but it's slightly noticeable)?

    Any thoughts welcomed
    Last edited: 18 Feb 2023
  2. play_boy_2000

    play_boy_2000 ^It was funny when I was 12

    25 Mar 2004
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    Likely the DP adapter does not support the bandwidth for 4:4:4. Movies and games are fine with 4:2:0 (any compressed video is encoded this way), but text looks like crap.
  3. Sentinel-R1

    Sentinel-R1 Chaircrew

    13 Oct 2010
    Likes Received:
    YCbCr is designated as 4:n:n. The 4 represents a sampling rate of 13.5 MHz, which is the standard frequency (ITU-R BT.601) for digitizing analog NTSC, PAL and SECAM. The next two digits represent the Cb and Cr rate. Each 8x8 matrix represents a "macroblock" of 64 pixels in a video frame.

    4:4:4 (Cb/Cr Same as Luma) Cb and Cr are sampled at the same full rate as the luma. MPEG-2 supports 4:4:4 coding, but having the same number of color difference samples as the luma is considered overkill and not worth the additional bandwidth to transmit it. When video is converted from one color space to another, it is often resampled to 4:4:4 first.

    -Nabbed to explain it better than I wanted to but essentially, your DP to HDMI link is lacking bandwidth, so that's either the cable or your graphics card.
    adidan likes this.

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