dylanraga's original repo contains a great explanation on what is causing a "washed out" look or raised black levels when viewing SDR or AutoHDR content in Windows' HDR mode, and has some alternative workarounds for the issue.

This fork uses an AutoHotkey script + ArgyllCMS dispwin workaround heavily based on mspeedo's .ahk script, which was written using dylanraga's formulas.

Using AutoHotkey allows fast toggling of the gamma transformation, which is useful because the gamma correction can be detrimental to real HDR content, which do not suffer from the same issue this workaround tackles. This method also optionally allows reloading Windows' color calibration with the hotkeys. See Windows color calibration reload function below for more info.

1. Download HDRGammaFix.zip from the releases page and extract it to an easily accessible location where it can reside permanently.
2. Run SETUP.bat as administrator.
   • SETUP.bat can also be run without admin permissions, but 'run at startup' tasks cannot be created.
3. Follow the prompts that appear and enter your preferred values.
   • Your SDR content brightness slider value can be found in Windows' HDR settings. For extra info, go to the SDR content brightness slider guide below.
4. The script will start running and can be controlled with hotkeys.
   • Use Win+F1 to disable gamma changes and Win+F2 to apply them again.
5. You can also run the script manually from HDRGammaFix.exe, but only after the initial setup.

• SETUP.bat needs to be run again if SDR content brightness value or gamma need to be changed.
  • Running as administrator is not required when only changing these two settings.

The default hotkeys are as follows:

• Win+F2

  or

• Win+Shift+2

• Win+F1

  or

• Win+Shift+1

• Win+Shift+3

• Run Uninstall.bat in the "uninstall" folder as administrator, and it should remove the task from task scheduler, if it exists.

• The script (if running) can be closed from the system tray in your taskbar by right-clicking the green "H" icon.

Find your SDR content brightness slider:

• Windows 11: https://www.elevenforum.com/t/change-hdr-or-sdr-content-brightness-for-hdr-display-in-windows-11.7832/

• Windows 10: https://www.tenforums.com/tutorials/146775-how-change-hdr-sdr-brightness-balance-level-windows-10-a.html

After you've set the slider to where you want it, enter the number that pops up when hovering over the slider's button in the setup.

If you've used Windows' HDR Calibration app (Windows 11 only) and applied a profile with it, there can be certain situations where it fails to apply.

This can happen after your display goes to sleep mode and wakes up again, or after your PC enters sleep mode and resumes. Reloading Windows' color calibration when applying the gamma transformation will fix this issue without having to open Display settings or Color management.

For reference, below is a table with Windows SDR content brightness slider values and their corresponding SDR white nit values, in case you want to set it up with an SDR white of exactly 100 or 200 nits for example. Credit goes to dylanraga's original repo.

• The gamma ramp correction will persist when toggling HDR (including via the keyboard shortcut), making SDR appear darker. When disabling HDR, make sure to revert the gamma correction using the hotkey. Likewise, when re-enabling HDR, you have to re-apply the gamma correction again.
• If you have an NVIDIA GPU, make sure the NVCP desktop color settings is set to "Accurate" or "Enhanced" mode; the correction will not apply in "Reference" mode.
• Pixel values above diffuse SDR white are untouched; a soft shoulder was added toward unity to blend the curve mapping with HDR values (Not done by me, all credit goes to dylanraga)

This workaround uses ArgyllCMS' dispwin utility to apply the gamma correction and AutoHotkey to run the script.