Models
This is not a conclusive list of models, it's just some of the ones I end up using the most, and a quick overview of them, but a surprisingly large part of upscaling comes from knowing when to use what models, and what the different ones are good for. This is not a 100% accurate list either, this is simply based on what models I use, and what I know of them, if you see anything wrong, then please feel free to correct me.
A lot of textures have compression artifacts such as dithering or banding, these artifacts can significantly make textures harder to upscale, but luckily, there are many models out there designed to combat this.
This is a 1x model by N00MKRAD, it's meant to fight JPEG compression artifacts, but it's good at compression in general. It can often be a bit too much for most images that only have minor compression, and is not often the best cleanup model there is, but it has its use cases.
Ditherdeleter is a 1x model by Mutin Choler, it's been the best I could find for about 30% of textures I've cleaned up, it can be a bit excessive at times, but if it's a relatively heavily noised image like the one below, it's the one I would recommend.
Bandagesmooth is a 1x model by Mutin Choler, it's designed to remove banding, and it's good at pictures with minor compression, it's at a level where it's not excessive enough to ruin a lot of textures, but still strong enough to properly prepare most textures before upscaling. But it's not the most optimal one for textures with more heavy compression.
These are upscalers that usually provide some smooth and often cartoony looking results, while also more or less preserving all original details, and adding very few.
This is a 4x model Mutin Choeler that's probably the definition of this category, it somehow manages to make almost all textures preserve their original identity while also smoothing them out a whole lot, it doesn't add any new detail, but somehow manages to preserve all original detail in a higher resolution. But its greatest weakness is also its greatest strength, it just makes the same image but at a higher resolution, there is nothing new about it, and it doesn't add extra stuff to the image to compensate for the higher resolution, so they often feel quite empty.
This model is a 4x model by Twittman that is kind of similar to PixelPerfect, but it tries to sharpen edges more and add more detail, it's not going to be optimal for something like a painting, or another simplistic surface, but it manages to sharpen and add more detail where Pixelperfect fails to do so, so just these two models should cover quite a lot of ground.
Digipaint is a 4x model by TheAtheistGod, it's meant for upscaling paintings and taking stuff like brush strokes into account, it's generally very similar to PixelPerfect, but it gives the picture a more painted aesthetic, which can be both a plus or a minus. It usually looks less sharp than Pixelperfect, but it gives a nice painted aesthetic that makes it favourable to use at a later point in upscaling.
BSRGAN is a 4x model by cszn, Me putting it in this category will probably be pretty controversial, it's kind of an everything upscaler, but it works fairly well for pixel art, and is so smooth that I wouldn't feel comfortable putting it in any other categories. It's a model that's good for not just pixel art and stuff, but also a bunch of other stuff. It's a very innovative model and ahead of most other models in a lot of ways, but it can also be a bit unpredictable, it's good to try it out regularly, but it also is often bad at pixel art and smooth textures, but also isn't too good at photorealistic stuff, but it's decent at stuff in-between.
These upscalers upscale textures realistically, they're good for adding grain and sharpening an image, but too much of them can cause textures that a too sharp, they work well in combination with the above upscalers though.
Sourcetex is a 4x upscaler by N00MKRAD, it's good for general grainy textures. It's good at adding detail and working on variety of different stuff, it is often too sharp though, and often reduces colours in textures down to colours in whatever its upscaling, rather than interpreting it as depth, so it sometimes flattens textures. It's a very powerful upscaler, but you must know how to use it properly for that to be the case.
Superscale is a 4x/8x upscaler by N00MKRAD, it's designed for upscaling real world images, and is therefore not always the best for textures, but that and other factors in its nature causes it to be more smooth and abstract than other upscalers, which can be useful when creating extra details from nothing, or when you need something a bit smoother than the other upscalers provide.
Siax is a 4x model by N00MKRAD, it's kind of like a fusion between superscale and sourcetex, it's not necessarily made for texture upscaling, but it's still good at it, while it also has many of the perks of Sueprscale. It's not very good at low res textures, but it can be combined with Sourcetex to use Sourcetex like upscaling while still preserving image depth.
