Follow these steps.

1. Download ReShade 3.4.1 from the official website[www.reshade.me].

2. Run the installer and when it says "Select game", choose ..\Steam\steamapps\common\Assassins Creed Odyssey\ACOdyssey.exe. Once you have selected the .exe remember to click the DirectX10+ option.

3. When it asks you to download the shader types click Yes but select only Adaptive Sharpen, Clarity, Colorfulness, FakeHDR and Vibrance. You can of course use any shader you want, but I have only tried a handful so I can only recommend the ones above.

Once the game starts up you should see a box appear in the top left corner saying "bla bla ReShade successfully installed", or something along those lines. That means that it worked.

4. Once you're either in the main menu or ingame you press Shift+F2 to get the ReShade menu to open. When that's done you just follow the easy tutorial which shouldn't take more than a few seconds. After you click "Finish", remember to check the little boxes on the left to activate them. You can also go in the ReShade settings menu to change the toggle button(I prefer Home) to see clearly see the effect ReShade has.

5. When the tutorial is complete you can mess around with the settings, select which shaders work best for you, or just delete it if you're unhappy with the final result.

Will add more screenshots..

Use ReShade at your own risk.

ReShade does not alter any of the game's files so you shouldn't worry about getting in trouble, especially in a single-player game. I've been using it for years on both SP and MP games and I've never had a problem.

I haven't really checked but I do know that after using ReShade for 10+ hours on Odyssey I haven't experienced any significant fps loss. Your results may differ.

To delete it go into the Odyssey folder. Then delete dxgi.ini, dxgi.dll and the reshade-shaders folder.

Note that this exact "recipe" can be used for many other games. I've had big success with it on Arma 3, theHunter: COTW, Squad, Rising Storm and many more.