Color Banding: HDR + Chroma + 10 Bit Problem (iOS 11.2)


I just played around with iOS 11.2 and the automatic rate switching. I encounter a problem with color banding eg. when watching “The Martian”. The scene in the beginning at 1:50, you can see the sky on mars which should show a clear color gradient. However, with Infuse the TV switches correctly to 4K HDR but there is lots and lots of banding. I assume that there is some problem when automatically choosing the color depth (10 bit) and the chroma mode (4:2:2 vs. 4:2:0). It looks like the color depth is somehow switched to 8 bit which would explain the banding. But since the material is 24p, both chroma modes should support 10 bit. Can someone reproduce this? Could also be related to a recent change to a new AVR (Denon X1400), but I think that thing does not touch the video stream.

On a sidenote, in 4K HDR, 24 Hz, 4:2:2 the Homescreen also shows lots of banding when you create that shine effect on the icons. 4:2:0 can not be chosen however, so it also might be some system bug?

Any insight is appreciated.


If your video is passing through an AVR make sure that the AVR is in bypass/direct whatever it is called on your model. This is usually under HDMI settings. A lot of AVRs do things to the video if they’re in “movie” or “game” or some other mode that can cause banding on 4K and anything above 4:2:0.

I just tried to connect the Apple TV directly to the TV (eliminating the AVR suspicion) and discovered that the Bug is either related to the TV or or Apple TV. Generally, it persists but it only happens when the input mode for the HDMI is set to PC (that is a special mode on the 2017 LG OLED models). In any other mode, the colors and banding are a non-issue.

I guess this makes it either a problem of the TV which does not announce its modes correctly or the Apple TV which does not understand the modes correctly. My money is on the TV unfortunately. Maybe someone sees this and it helps them. I’ll try to go with a non-pc mode but I’ll have to check first what I loose doing this. :frowning:

  • scurra

PC mode modifies the way colors are handled.
If you have chroma subsampling (and you always have for 4K HDR on Apple TV 4K, be it 4:2:2 or 4:2:0), colors are only encoded in 19202160 or 19201080 instead of 3840*2160.
In non-PC mode, color information is processed as it should be for video.
In PC mode, it is processed so that text and documents look OK (a lot sharper than in the non-PC mode) but with the side effects you mentioned for video.

Side note: chroma subsampling is necessary in order to fit a 4K 60p 10 bit(HDR) video into the bandwidth available in HDMI 2.0a (36Gbps).
(4K) UHD Blu-Rays have 4:2:0 chroma subsampling (color encoded in 19201080). Apple TV 4K is actually better than UHD Blu-Rays since it allows for 4:2:2 chroma subsampling (colors encodes in 21601080).
Since the human eye is more sensitive to luminance(brightness) than chrominance(colors), in practice, this is not a problem.