This tool uses an undocumented NVIDIA API, supported on Fermi and later, to convert colors before sending them to a wide gamut monitor to effectively clamp it to sRGB (alternatively: Display P3, Adobe RGB or BT.2020), based on the chromaticities provided in its EDID. AMD supports this as a hidden setting in their drivers, but NVIDIA doesn't because ???.
ICC profiles are also supported and can be used in two different ways. By default, only the primary coordinates from the ICC profile will be used in place of the values reported in the EDID. This is useful if you want to use a profile created by someone else without taking their gamma/grayscale balance data into account, as that can vary a lot between units. If you enable the Calibrate gamma to checkbox, a full LUT-Matrix-LUT calibration will be applied. This is similar to the hardware calibration supported by some monitors and can be used to achieve great color and grayscale accuracy on well-behaved displays.
Extract release.zip somewhere under your user directory and run novideo_srgb.exe. To enable/disable the sRGB clamp for a monitor, simply toggle the "Clamped" checkbox. For using ICC profiles and configuring dithering, click the "Advanced" button.
Generally, the clamp should persist through reboots and driver updates, but it can break sometimes. You can choose to leave the application running minimized in the background to have it automatically reapply the clamp and also handle HDR toggling – see the section "HDR and automatic reapplying" below.
If the checkbox for a monitor is locked, it means that the EDID is reporting the sRGB primaries as the monitor's primaries, so the monitor is either natively sRGB or uses an sRGB emulation mode by default. If this is not the case, complain to the manufacturer about the EDID being wrong, and try to find an ICC profile for your monitor to use instead of the EDID data.
The reported white point is not taken into account when calculating the color space conversion matrix. Instead, the monitor is always assumed to be calibrated to D65 white.
Any change in the display setup (such as a monitor being added/removed) will cause the clamp to be reapplied on all monitors, as long as the application is running in the background. The main purpose of this is to handle HDR being toggled in Windows, as the clamp will automatically be disabled for monitors for which HDR is enabled (since colors would get messed up otherwise). Additionally, you can use the "Reapply" button to manually reapply the clamp in case something breaks (e.g. due to a driver bug).
Minimizing the GUI will hide it from the taskbar, so that it'll only be visible in the tray. If you want to run it on boot, you can enable the "Run at startup" checkbox, which will use the -minimize command line argument to make it start minimized.
Since version 531.79, the NVIDIA driver rejects any attempt to set a color space conversion while HDR is enabled with error -104 (NVAPI_NOT_SUPPORTED). This means that the HDR handling mentioned above does not work anymore. I don't know whether this is a driver bug or an intentional change, but I don't think I can do anything to fix it.
The color space transform does not get applied properly to the mouse cursor, which results in it having wrong gamma and colors. This should be hardly noticeable with the default Windows cursor. Workaround: Force software rendering of the cursor, e.g. using SoftCursor.
Windows HDR is handled properly, but NVAPI HDR, which some applications use to output HDR even though Windows HDR is off, will result in wrong colors while the clamp is active. To work around this, you can either enable Windows HDR or disable the clamp manually before launching such applications.
Applying any kind of calibration on the GPU-level usually results in banding unless dithering is used. By default, NVIDIA GPUs do not apply dithering to full range RGB output. Therefore, it is recommended that you use the dither controls to enable and configure dithering. "Bits" should be set to match the bit depth of your GPU output, and "Mode" can be set to whatever looks best to you. Note that "Temporal" works by rapidly switching between colors, which some people's eyes are sensitive to.