Chrome/Chromium and Image Viewer distort colours if a colour profile is enabled.

[brandon lockley]

Using Ubuntu 18.04.1 LTS
Running on an i7-6700k with a GTX 1080
Reproducible with nvidia-driver-396 or xserver-xorg-video-nouveau
and a single 4K screen (TV) connected via HDMI.

The issue:
Any dark content displayed by an effected application (e.g. a very dark image or dark themed web page) is much darker than intended making it almost unusable.

This only effects applications that are launched when the 4K screen is connected. If i disconnect the 4K screen, launch the app via a different 1080p monitor then reconnect the 4K screen the app remains unaffected.

The only apps i have found so far that are effected by this are Google Chrome and Image Viewer. That said this is only noticeable when the app is displaying dark contend so if other apps are affected it may be impossible to tell.

The attached screenshot uses a black to white gradient image to clearly demonstrate the issue.
Is seems like it may be an issue with colour depth as bellow a certain brightness it just goes strait to black.

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

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[brandon lockley (brandon3055)]

Given the nature of this issue i can not think of a way to narrow it down to a specific package.

[Daniel van Vugt (vanvugt)]

Always remember a TV is not a monitor. Monitors are made to respond to colour more accurately than TVs, out of the box. If you want to use a TV as a monitor then you will very likely need to change a lot of settings in the TV itself to make it behave more like an accurate monitor. I know it's annoying, hardly any TV manufacturers do this out of the box.

The first thing to remember is that the HDMI spec requires that HDMI displays respond to colour differently than non-HDMI (computer monitor) displays. The HDMI spec says that all values 0-16 are full black and all values 235-255 are full white. This is called limited RGB mode and you will need to tell BOTH the Nvidia driver and the TV to switch to full range RGB mode instead so that they render shades more accurately like a monitor.

As a second preference, you should be able to tweak the gamma values in the nvidia settings utility. Your gamma exponent looks too high so reducing it will bring back those missing shades.

You can also choose a colour profile in Settings > Devices > Color which may help to change the gamma curves to your liking.

I hope you find a solution in one of those.

Unfortunately since you're using a graphics driver that's not from the Ubuntu archive, we can't really handle bug reports about that here.

If you are willing to downgrade the driver to a supported version like https://launchpad.net/ubuntu/+source/nvidia-graphics-drivers-390 then you can open a new bug report by running:

  ubuntu-bug nvidia-driver-390

[Daniel van Vugt (vanvugt)]

In your TV settings, if there is nothing called limited/full range RGB then often it will just be called the "Black Level".

Quote from bug 1668159:

if your device doesn't yet support changing the setting, and your HDMI-connected TV looks a bit wrong then you can probably just change the TV settings:

Picture is too dark/black: Likely problem is that your device is outputting full range and your TV is expecting limited. Change your TV settings to Black level = Normal or High

Picture is washed out (blacks appear grey and whites are dim): Likely problem is that your device is outputting limited range and your TV is configured for full range. Change your TV settings to Black level = Low (which means to treat 16 as full black and 235 as full white).

[brandon lockley (brandon3055)]

I don't think this is the TV. If it was this would only affect what is displayed on the TV itself and it would affect everything on the screen the same. But as you can see from the screenshot this only affects certain applications. I also have 2 regular 1080p monitors attached and it does not matter what screen i put the affected application on its the same. It may be a colour depth issue but unless that is application specific and having this screen attached throws off the colour depth of my other 2 screens i dont see how this could be related to the TV.

It does seems like ubuntu has some issues with 4K screens. Im not sure if these are related but i also experience this issue which has nothing todo with the screen being a TV https://forum.manjaro.org/t/gnome-night-light-is-lime-green-at-4k/48376

[Daniel van Vugt (vanvugt)]

* That "lime green" problem is something we noticed a year or two ago. Some people had lime green and others (me!) just had washed out colours, specifically only in Chrome and some image viewers (sound familiar?). The fix for everyone was to delete and disable the default colour profile in Settings. So maybe that's all you're missing... Remove it.

* The resolution "4K" or "1080p" is irrelevant here. What is more relevant is that it's a TV connected via HDMI. And TVs connected via HDMI are subject to the HDMI spec which says:

  "While using RGB, Limited Range shall be used for all video formats
   defined in CEA-861-D, with the exception of VGA (640x480) format,
   which requires Full Range."

But what I hadn't told you yet is that despite it being in the standard, not all manufacturers honour it. Because dishonoring it like a proper monitor yields better image quality, and that's likely what HDMI monitors (not TVs) will do by default already. But your monitor and TV's default settings might be the other way round. Regardless, please check the HDMI RGB range (or "Black Level") settings in BOTH your Nvidia driver and in the TV and monitor own menus. To get a correct picture they need to be the same in both the graphics driver settings and in the TV's own settings menus. I can't give you any more specific instructions because it's different for every model of display :(

[brandon lockley (brandon3055)]

Interesting... So i did what you suggested and deleted the colour profile for the display and that did fix the issue with chrome and image viewer. However it did not fix the green night mode issue. Oh well the problem i came here for is fixed so thanks for the help!

[Daniel van Vugt (vanvugt)]

Great!

I checked and it was only a year ago that the rest of us noticed the problem and found a solution (including Matthew Paul Thomas, Robert Ancell and myself).

If the problem is still occurring in 18.04 then we need to do something about it. That something is to ensure Ubuntu ships with NO ACTIVE colour profile, which has been the fix for all of us so far...

[Daniel van Vugt (vanvugt)]

On the other hand, maybe we need to treat disabling the default colour profile as a workaround.

I forgot to mention that in at least one case I noticed similar problems in web browsers and image viewers even when using a properly custom calibrated profile for my display.

So a real fix might have to come in the apps themselves, or maybe just one or two image decoding libraries that are misinterpreting the profile data (maybe they don't know or expect the whole compositor is applying the profile already?). To do this someone would need to dig into the code of an affected app and see how/where it is using the colour profile data.

[brandon lockley (brandon3055)]

So a little off topic but as it seems to be related do you have ant thoughts on why this didn't fix night mode in my case? In case you missed in in my previous post deleting the colour profiles fixed chrome and image viewer but did not fix the night mode issue.

[Daniel van Vugt (vanvugt)]

I guess night mode works by applying a colour profile in much the same way as any other colour profile. So night mode would continue to experience similar problems even without a custom profile installed. Night mode IS a colour profile so it may well hit the same bug.

I now think we should be focusing on fixing the affected apps, maybe just one or two broken libraries. In the meantime, keep in mind disabling colour profiles is a good workaround.

[Olivier Tilloy (osomon)]

Is this affecting chrome AND chromium, or only the former, by any chance?

[Daniel van Vugt (vanvugt)]

@osomon,

Just verified both chrome AND chromium (v70) experience this bug. The colours are ugly and dull when a colour profile is active. It's immediately obvious in the Google logo on the search page. And the problem goes away as soon as I remove the colour profile and restart the browser.

[Daniel van Vugt (vanvugt)]

The greenish problem is now being tracked separately, in bug 1803840.

[Sebastien Bacher (seb128)]

the issue is similar to bug #938751, could be a duplicate

[Daniel van Vugt (vanvugt)]

Yes. Let's use bug 938751.