Taming the Wide Gamut using sRGB Emulation

Author: Adam Simmons
Last updated: September 12th 2021

 

What’s the issue with a wide colour gamut?

The colour gamut reflects the range of colours that a monitor can output and defines its limits of saturation. Monitors with wide colour gamuts are becoming increasingly common, with a range of backlight technology now available to facilitate this at relatively low cost. The rise of HDR (High Dynamic Range) has accelerated this, with good coverage of the DCI-P3 colour space the near-term goal. Most content we consume under SDR (Standard Dynamic Range), on the other hand, is designed around the sRGB colour space. This includes games as well as most image and movie content, where the creators have the sRGB colour space in mind. It’s still the common standard for displays under SDR; wide gamuts are not universally supported and sRGB remains the lowest common denominator.

If you view this content designed for the sRGB colour space on a screen with a wider gamut than sRGB. And you aren’t controlling the gamut using one of the methods described below. Then things appear more vibrant and saturated than they should. This is different to a digital saturation boost, such as Nvidia’s Digital Vibrance Control or a saturation slider in the monitor’s OSD. Things aren’t simply pulled closer to the edge of the gamut without that gamut being expanded, which crushes shade variety. Good spacing is still maintained between shades on the gamut and strong variety remains. Some users like this varied but more vibrant and saturated look, others do not. And if the gamut is a lot wider than sRGB things are taken to the extreme in that respect. We describe these effects in our reviews of such monitors, for example the Acer XB323U GP, which is afforded a very wide gamut by its Quantum Dot backlight solution. In games and other content designed for sRGB, untamed wide gamuts like this can produce a range of issue. Overly tanned or sometimes sunburnt-looking skin tones, reddish brown earth appearing far too red, yellowish green vegetation appearing overly yellow and somewhat garish, artificially vibrant sky blues to give just a few examples. The colour gamut below shows the native gamut of the Acer XB323U GP (red triangle) compared to DCI-P3 (blue triangle) and sRGB (green triangle).

Colour gamut XB323U GP (native)

Colour gamut XB323U GP (native)


What can we do to control the gamut on the monitor?

ICC profiles provide gamut mapping corrections for ‘colour-aware’ (‘colour-managed’ or ‘ICC aware’) applications such as web browsers and photo editing applications. Unfortunately, this does not include games for a basic software-based profiling. And unless you’ve created the profile on your own screen using your own colorimeter, it will suffer when it comes to accuracy. Some monitors provide an sRGB emulation mode, which clamps the colour gamut so it more closely tracks sRGB. Ideally with little extension beyond and as little under-coverage as possible. Such a setting is fairly widespread but not always found on wide gamut displays. Even if such a setting is present, it’s unfortunately common for sRGB emulation modes to lock off brightness, which means the setting can be inappropriate for many if it doesn’t fit their own sensitivities and preferences. If not, it’s extremely common for them to lock off access to other settings such as colour controls and gamma settings. The sRGB emulation setting of the Acer used in this example allows brightness to be adjusted, but the colour channels and gamma settings are inaccessible. Adjusting gamma and colour balance is ideally done through the monitor OSD as doing so using the graphics driver can negatively impact the image in various ways, including the contrast and shade variety. Reduction in the latter can induce banding, with crushing together of closely matching shades. Even if using a colorimeter or similar device, it’s best to adjust as much as possible through the monitor’s OSD. Also note that no setting in the graphics driver controls backlight brightness – just digital brightness controls which are very different indeed and can’t reduce brightness without a hit in contrast. The image below shows the Acer XB323U GP’s colour gamut (red triangle) compared to sRGB (green triangle), using its sRGB emulation mode.

Colour gamut XB323U GP ('sRGB' mode)

Colour gamut XB323U GP ('sRGB' mode)


What can we do to control the gamut in the graphics driver?

AMD GPU drivers offer an alternative, a flexible sRGB emulation setting that is activated in the driver itself. This setting reads the EDID (Extended Display Identification Data) of the monitor which contains information on the native gamut and corrects based on that. These corrections apply universally, including to full screen games and other applications. It has actually existed for some time, but the naming never made it clear what it did so even more technically-minded users may have overlooked it. In older graphics drivers there was a ‘Colour Temperature’ toggle that could be set to ‘Automatic’ rather than the default ‘6500K’ to achieve sRGB emulation. In newer drivers it’s done by opening ‘AMD Radeon Software’, clicking ‘Settings’ (cog icon towards top right) and clicking on ‘Display’. You should then ensure that the ‘Custom Color’ slider to the right is set to ‘Enabled’ and ‘Color Temperature Control’ (CTC) set to ‘Disabled’. It may appear to be set this way by default, but the native rather than restricted gamut is likely in play. If that’s the case, simply switch the ‘Color Temperature Control’ slider to ‘Enabled’ then back to ‘Disabled’ to leverage the sRGB emulation behaviour. This is shown in the image below.

AMD Color Temperature Control disabled

We’ve tested this on a broad range of monitors and have found it does usually offer reliable sRGB emulation. Exactly how closely the gamut tracks sRGB varies between models, but we typically see ~98% sRGB coverage (sometimes a touch below, sometimes a touch above) with very little extension beyond sRGB. The beauty of this setting is that you use it in conjunction with the full native gamut of the monitor, allowing you to use the full array of monitor OSD settings available to you. It’s set universally, too, so isn’t something that is simply ignored by some applications. The colour gamut below shows the Acer XB323U GP set up to use its native gamut, all OSD options accessible, but with CTC disabled in the AMD driver.

Colour gamut XB323U GP (AMD CTC disabled)

Colour gamut XB323U GP (AMD CTC disabled)

Note: Under HDR you will likely end up with upset image balance and intense oversaturation by disabling CTC. This tweak is only designed for viewing sRGB content under SDR.

Nvidia doesn’t include a similar feature in their graphics drivers, but the Nvidia GPU and driver pipeline does actually include a ‘hidden feature’ that works in a very similar way. A tool called ‘novideo_srgb’ can be downloaded here and is discussed in this Reddit thread. Download the latest ‘release.zip’ file and extract the contents to a destination of your choice. Run ‘novideo_srgb.exe’ (Microsoft Defender SmartScreen may flag this as an unrecognised file initially) and click the ‘Clamped’ checkbox. The same EDID data read by the AMD alternative is used and the resulting gamut is extremely similar. The corrections apply universally, including to full screen games and other applications. If you find the checkbox is already enabled and you can’t ‘apply the fix’ as expected, try the alternative build mentioned in this Reddit discussion. The video below covers some of the points raised in this article and should start at the section which covers this tool. Note that the gamut clamp should only be used under SDR, as with the AMD toggle. Leaving it enabled under HDR will upset image balance, although in a different way to AMD’s toggle – it will provide significant undersaturation.



What we’d like to see

Monitors continue to push firmly into the wide gamut territory, but a lot of content is still developed or designed to be consumed within the sRGB colour space. Whilst some models offer a good and flexible sRGB emulation mode, many do not. And whilst users with an AMD GPU might be able to get around that, users with Nvidia or Intel graphics hardware aren’t so lucky. So this is what we’d like to see from both monitor manufacturers and GPU manufacturers:

  • Include a flexible sRGB emulation setting, brightness adjustment should be considered the bare minimum. Models like the ASUS PG27UQ and PG32UQX show how this should be done by offering an sRGB emulation setting which does not lock off or interfere with other settings. Some ‘G-SYNC Ultimate’ models such as the Dell Alienware AW2721D and AW3821D offer a wide gamut (95%+ DCI-P3) without any sRGB emulation setting. Which is anything but ‘Ultimate’ when it comes to universally accurate display of sRGB content.
  • For models with a particularly wide gamut, including extension well beyond DCI-P3 in some regions, a DCI-P3 emulation mode would be helpful. Or perhaps an ‘sRGB+’ setting that cuts the gamut down to a bit beyond sRGB. Professional and colour-focused wide gamut models such as some from the BenQ SW series and some Dell UltraSharp models may offer a DCI-P3 setting, but it’s usually lacking on gaming monitors. Some users like a boost of vibrancy of saturation, but not to the extent seen on some models with a very wide and untamed gamut.
  • Gamers and content creators alike can appreciate features such as hardware calibration (a hardware-addressable LUT) on the monitor. Allowing them to use a colorimeter or other calibrator to essentially create a calibrated preset for the monitor with the colour space of their choice. Some gaming-oriented models in the likes of the LG UltraGear series offer this. But it’s quite a rare addition on gaming monitors.
  • Nvidia (and Intel) should both strongly consider a driver-side sRGB emulation setting like AMD offers with their ‘Colour Temperature Control’ feature. Many people were quite excited when Nvidia introduced a feature in the driver called “Color accuracy mode”, including us. But alas; this is not an sRGB emulation setting.
  • “Colour accuracy mode” seems a more appropriate name for a driver-side sRGB gamut clamp than disabling something called “Colour Temperature Control”. AMD should consider renaming this setting so it’s more obvious what it does and perhaps displaying it more prominently in the driver. It’s a very useful setting but many are unaware of it.


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