I Tested 7 Best Upscalers on Stable Diffusion + Supir (AI Upscaler Tool)

Hey, what's up? 👋

I'm Jakob, a digital artist, working on AI-generated content (NSFW included) and today I'll talk about Stable Diffusion upscalers.

Today I compared eight image upscalers.

Click here to check the results of the Comparison between upscalers

Or read first:

• What is an Upscaler?

• How to use it?

And if you are lost and don't even know what Stable Diffusion is, go to this article where I explain it a bit, but basically, it's an image generator.

What is an Upscaler? How does upscale on Stable Diffusion work?

An upscaler makes a picture better by making it bigger and clearer. 🔍

It takes a small picture and makes it larger without losing details.

Take a look:

Is upscaling good or bad?

Upscaling can be very good because it makes pictures clearer and bigger.

But sometimes, it can make things look a bit strange or blurry if not done right.

It’s important to pick the right upscaler for the job.

Comparison between upscalers

For this comparison, I used 8 images, and for each of them, I tested 7 upscalers that are default in Stable Diffusion plus SUPIR, which is another upscaler.

If you want to see the full-size comparison, open the link just below the photo.

Photo 1

Full image

Photo 2

Full image

Photo 3

Full image

Photo 4

Full image:

Photo 5

Full image

Photo 6

Full image

Photo 7

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Photo 8

Full image

Look at the side-by-side comparisons of these results to see the differences for yourself.

Based on these comparisons:

Models that gave better results:

• Supir

• ESGAN 4x+

Intermediates:

• Lanczos

• Nearest

Not good for photorealism:

• R-ESRGAN 4X+

• ScuNET

• ScuNET PSNR

• SwinIR_4x

Here are some thoughts on each model individually:

R-ESRGAN 4x+

This one didn't perform well for realistic images. It seems to work better for anime, as it tends to make the outlines darker, almost like cartoon lines.

ScuNET and ScuNET PSNR

I didn't notice much difference between these two.

They performed better than the R-ESRGAN 4x+ for realistic photos, but yet not that good.

SwinIR_4x

This upscaler did a good job maintaining the natural look of the photo, but it gave the images a smooth, almost like Instagram's skin correction filters.

Nearest

This one seemed a bit better than the first three, but sometimes you might end up with a pixelated image.

Also, the skin tone looks more reddish, see the full image

Lanczos

Better than Nearest, it fixes small pixelated details and keeps the image clearer when resizing.

ESRGAN_4x

This is the best default upscaler available on the Automatic1111.

Similar to Lanczos but it has a more natural color tone.

SUPIR

SUPIR was the best among all for the majority of the photos.

The main disadvantage is that you don't have it as a default on Stable Diffusion.

But don't worry, here in this same post I will teach will how to use Supir easily.

⚠️ Important Considerations and Exceptions

It's important to note that these results should not be taken as a definitive guide.

There can always be exceptions where a Upscaler that generally performs poorly may outperform a typically better model in certain scenarios, and vice versa.

So, use this comparison as a reference, not a golden rule.

Here are some examples of things that happen differently:

For example, the Supir, which usually gave the best results, did very poorly in this photo here:

It even deformed the face. This probably happened because it was a more distant photo.

Another thing that happened in this same grid of photos was that the Lanczos were the best for this photo.

It did not try to correct and perfect the photo, which made it look more realistic than the other models.

So, it's worth trying different upscalers and not just focusing on the ones that are the best most of the time.

How to use an upscaler?

The first 7 upscalers are default in the Automatic1111 Stable Diffusion.

To use them:

First, open the Stable Diffusion WebUI:

1. Go to the 'Extras' tab.

2. Upload the photo you want to upscale.

3. Select the upscaler in 'Upscaler 1', (if you want to mix with another, upload it in 'Upscale 2' and adjust the weight).

4. At the "Scale By" tab, set the proportion you want to increase for example 2x times bigger, and click "Generate".

You can also select "Scale to" at step 4 and define the final resolution you want.

How To Use Supir

To install Supir, you need to know how to use ComfyUI and other advanced stuff.

To make it easier, I'll give you some links where you can test Supir online without installing anything.

If you still want to try to install and run it on your computer, I have left a video tutorial at the end.

Here are the ways to use Supir online for free:

Replicate.com:

OpenArt:

You can use it for free and online if this button is present on the workflow page:

And of course, if you have ComfyUI installed, you can download the workflow and run it locally

Flowt:

To use it, just click the button: "Try on the cloud":

Installing Supir on Comfyui

In the following video, the youtuber Stephan teaches how to install and use SUPIR on ComfyUI.

Got more questions about Upscale or Stable Diffusion?

Click here and leave me a message (it can be anonymous!).

Tell me what you think or if you have any questions, also leave feedback so I can keep improving.

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