[GTALUG] war story: fixing an LCD TV

[Lennart Sorensen]

On Sat, Jun 01, 2019 at 05:39:15PM -0400, D. Hugh Redelmeier via talk wrote:
> HDR (High Dynamic Range) means a confusing variety of things,
> especially after marketing has had at it.  But "normal" computer
> pixels have 8 bits per colour in each pixel.  HDR often means 10 bits
> per colour in each pixel.  So if you care about colour, you might want
> HDR.

8bit HDR does exist, but is rarely used since it tends to cause color
banding.

> You also need to worry about chroma subsampling (TVs often do this).

As long as you have HDMI 2.0 you should be able to use 8bit per channel at
4K and 60Hz without chroma subsampling (which ruins the clarity of text).
Goign to HDR requires either dropping the refresh rate or using chroma
subsampling.  Neither is likely to be that desirable unless you are
just doing photo editing and hence frame rate is less important than
color range or you are doing video in which case chroma subsampling
isn't an issue (it probably isn't a problem for photos either).

> There is some silly divergence.  Off the top of my head:
> 
> - monitors tend to be more expensive than TVs for the same level.
>   Quality improves faster in TVs (model lifetime is short).
>   I'm pretty sure this is a function of the market size.
> 
> - TVs only do HDMI or worse.  Monitors have DisplayPort, which
>   supports higher bandwidth (depending on the state of leapfrogging
>   standards).  Monitors generally support HDMI as well.
> 
> - Older HDMI standards didn't support UltraHDMI well
> 
> - TVs often do chroma subsampling, without being mentioned in the spec
>   sheets.  Monitors do not.

The TV does not do it, the signal sent to it may.  The TV uses whatever
it is sent, but if course what formats it supports varies so the source
device may not have a choice.  A monitor does it too if sent such a
signal.  Connect a bluray player to a monitor and you will get a signal
with chroma subsampling, because that is how video on bluray works.

-- 
Len Sorensen