If you are already using Upscale, which does just about the same thing as this mod, but through DLL mods instead of a GPU driver-feature, then check the stickied comment for an analysis on their differences. 

I'd recommend first using Fallout 4 Upscaler, as it supports DLSS/DLAA/FSR2/XeSS.
Keep in mind that DLSS/XeSS/FSR2 is INCOMPATIBLE with ENB, and DLSS/DLAA requires an RTX GPU in order to function, so you still may want to use NIS/Upscale.

Overview:

For people looking to take drastic measures to increase framerates, lowering your resolution is one of the last resorts, however, this will degrade the overall clarity of your game and make it look blurry as hell, which is where Nvidia Image Scaling (NIS) comes into play if you have a NVIDIA GPU.

It functions as a more accessible version of DLSS, just enhancing a stretched out image, but instead of utilizing a fancy neural-network AI that uses RTX tensor cores, it just slaps a sharpening filter from Nvidia over the image.

The upside is it operates on the driver-level, meaning it will work on any game as long as it's running in exclusive fullscreen mode, and if the game is running at one of the "scaling resolutions".

This tutorial will teach you how to get NIS working with Fallout 4. This also applies to just about every other game that you can adjust the resolution of.

Enabling NIS

First, you'll need to enable NIS in your settings. Make sure your drivers are up to date beforehand.

Open the Nvidia Control Panel. In the panel on the left, under "3D Settings", click "Manage 3D Settings", and find the "Image Scaling" option. 

Enable Image Scaling, and I'd recommend enabling the "Overlay Indicator" so you can make sure it's actually working.

There is a slider to control the amount of sharpening. Set it to whatever, I personally have it set to 40%. This helps remedy the "blurryness" effect, but you can also do the same with an ENB/Reshade.

Make sure to hit the apply button on the bottom right, and don't close the program yet.



Refer to the Nvidia's documentation for more information: "How to Enable NVIDIA Image Scaling"


Editing your INI Files

NIS needs a game to be running in exclusive fullscreen + at one of the supported resolutions to work, so you'll need to change these settings in your .INIs instead of traditionally where you change this in-game. Thank you Bethesda, very cool.

Open up your Fallout4.ini and Fallout4Prefs.ini, located in your Documents\My Games\Fallout 4 folder.

In your Fallout4.ini and Fallout4Custom.ini, verify/edit these values:


[Display]
iLocation X=0
iLocation Y=0


In your Fallout4Prefs.ini, edit the following values:


[Display]
bBorderless=0
bFull Screen=1
bMaximizeWindow=0


Now, go back to your Nvidia Control Panel, select "Change Resolution" on the left panel, and look at the "Scaling Resolution". Here you will find the various levels of scaling available. The ones in the image are for 1080p, and they will look different for any other resolutions.



Choose a resolution to scale from, I'd recommend 77% or 85%, as any lower will look extremely blurry, make text hard to read, and mess with the in-game UI scaling. That was the case when I tried 67% on 1080p. 

Do not switch your actual monitor's resolution to these scaled resolution, only change the game's resolution itself.

Input the chosen resolution values in your Fallout4.ini and Fallout4Custom.ini


[Display]
iSize H=SMALLERNUMBERHERE
iSize W=LARGERNUMBERHERE


CTRL+S to save the file, and then boot up Fallout 4. 

If you enabled the NIS overlay, a “NIS” text label will appear in the top-left of the screen. If it's green, that means Image Scaling is working as intended. If it's blue, then it's just sharpening, and not scaling.
 

And uh... yeah, it should work now, and you should expect an extra 5-10 FPS. Again, this should be your last step in trying to increase performance, before trying things like repacking all your texture mods into a .BA2 or following the "Optimization Guides Collection" or removing your big hot, dripping wet, extra bouncy tiddy physics mods.

I would also recommend applying the ini tweaks in Performance Optimizations Guide - Mod List & Tweaks, as you can get more performance, a few fixes, and some enhanced visuals from them.


Troubleshooting:

-Make. sure. you. input. the. resolution. values. correctly. Always double-check any values to make sure they are correct.

-If the game starts in a window/the top corner of your screen, kill FO4 in Task Manager, then do not ALT+TAB while starting the game, wait until you get to the main menu.

-If your game crashes and you cannot bring up task manager, Press WINDOWS+TAB, create a new desktop, and then open task manager there.

-If you have GeForce bloatware Experience installed, make sure it isn't "optimizing" your game for you, aka messing with your settings.

-If you use Mod Organizer 2, keep in mind that it, by default, uses it's own .ini files instead of the ones in your documents folder. I'd recommend just disabling this. 
---You can disable this by clicking "profiles" at the top, and unchecking the "use profile specific .ini files". This is profile specific, so if you, yknow, have multiple profiles with varying load orders, you may want to keep this enabled.


Please keep in mind that if you try to record the gameplay while the game is using image scaling, only the base, unscaled/unsharpened resolution will be recorded, unless you are using a capture card.


Anyways, hope you enjoyed.

If this guide helped you, consider endorsing. It will produce serotonin in my brain due to me seeing positive number on the internet for thing I created. 

If you've ran into any issues, and made sure to troubleshoot your issue beforehand, then post a comment documenting the issue's symptoms, and I might look into it, and update the guide to include the issue and fix. 



External Sources/Documentation:

What is Nvidia Image Scaling? Article by GPU Mag

From NVIDIA DLSS 2.3 To NVIDIA Image Scaling: NVIDIA’s Full Stack Of Scaling Solutions For Gamers Article by Nvidia

How to Enable NVIDIA Image Scaling Article by Nvidia

Nvidia Image Scaling vs AMD FSR vs DLSS - Which Works Best in Games? Video by Hardware Unboxed


The album I listened to while writing this it's a fuckin banger.