The Witcher 3: Wild Hunt has been criticized by gamers for offering visuals that are less than what the developers originally promised when they made their first reveal of the game in action back in 2013. Simply put, the game doesn't look quite as good as some might have hoped.
Fortunately, the developers have been releasing patches to improve the game's graphical fidelity, and on top of that, there are a number of ways to tweak the game to get it looking better than it does out of the box.
One new method of improving the game's texture definition has been discovered. Comparisons can be seen below:
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To make the changes, navigate to "…\Documents\The Witcher 3" and open the "user.settings" file with a text editor like Notepad, and then manually add the following section and variable at the very end:
[Streaming/Textures]
UseMipRefiner=true
The addition of this variable will force the game to use much higher quality mip textures, improving the visual fidelity of the game at little to no hit to the game's performance.
Remember to save your changes upon closing the "user.settings" file.
Source: Asmodean778 on the Witcher 3 forums.