It's confusing because both AMD and Nvidia call both frame gen and upscaling as the same thing.
Upscaling: GPU renders game at low resolution (eg, 720p), and then (semi) smartly guesses what's in the pixels that weren't rendered. You get improved framerates because the GPU is doing less work per frame. The downside is typically that the image is typically a bit blurrier, and depending on how the GPU guesses the missing pixels, you might also get ghosting, which is where moving objects leave a smear trail behind them.
Use when:
- your GPU isn't powerful enough to drive your monitor at its native resolution (ie you were going to run the game at a lower resolution anyways)
- your game isn't running as fast as you'd like, but turning down the settings would result in too noticeable of a drop in visual quality (the general consensus is that you should only use quality mode when upscaling, any lower and you'll get significant blurring)
- your game doesn't support your monitor's native resolution (common in older games)
Do not use when:
- you could turn down the settings and still be satisfied with the visual quality
Frame gen: GPU renders a frame, holds on to the frame, renders the next frame, and then guesses at what happened between the two frames. The framerate is improved because the GPU is inserting an entirely guessed frame in between every rendered frame. The downside is that because the GPU has to hold on to a frame, the latency is increased. More specifically, the time between when you move your mouse and when your camera moves will be increased with frame gen.
Use when:
- your game isn't latency-sensitive (eg puzzle games, strategy games, some adventure games)
- you have a high refresh rate monitor (higher refresh rates typically lead to less added latency)
Do not use when:
- your frame rate (without frame gen) is below 60 fps (added latency becomes too noticeable)
- your game is latency-sensitive (eg competitive multiplayer games)
Terminology:
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AMD FSR 1: semi-dumb upscaler
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AMD RSR: literally just FSR 1
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AMD FSR 2: semi-smart upscaler
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AMD FSR 3: very slightly smarter upscaler than FSR 2, and comes with semi-smart frame generation
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AMD AFMF: literally just the frame generation part of FSR 3, but slightly dumber
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nVidia DLSS 1: semi-dumb upscaler
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nVidia NSR: literally just DLSS 1
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nVidia DLSS 2: semi-smart upscaler
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nVidia DLSS 3: smarter upscaler than DLSS 3, and comes with semi-smart frame generation
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Intel XeSS: semi-smart upscaler