The software is made to create images at 512x512 but can create other image sizes and aspect ratios. It
technically can make larger images, but there is a limit to how large it can go, that is why the software includes an "Upscale" option inside it.
Through a
LOT of testing on my end I've learned that if you want 1:1 images your best bet is to try 768x768 as your largest image size. If you have a beefy GPU you can make a 1024x1024 image but it's going to have errors in it, or even one image duplicated and split up.
I like to make 4:3 aspect ratio images, and the largest that I've been able to reliably make without errors is 704x872 resolution.
Anything larger than 704x872 produces weird results on a constant basis. Over the course of 45 image results of "woman standing in front of a wall" it gave me separate images 31 times. It would either create 2 similar images with a split-screen effect, or just make multiple people. Typing "group, duplicate bodies, duplicate faces, multiple people" in the negative prompts did nothing to fix it
There are some model checkpoints out there that have been trained to make larger images, but even then they're not going to be what you're looking for if you're wanting HD resolution photos. I think the biggest I've seen is 768x768 checkpoints, and selecting any other resolution than that gives you errors all the time.
I've ran tests with the following resolutions, (each generating a batch of 45 images):
512x672: no errors
520x680: no errors
528x688: no errors
536x696: no errors
544x704: 3 errors, 42 good images
552x712: no errors
560x720: no errors
568x728: no errors
576x736: no errors
584x744: no errors
592x752: no errors
600x760: no errors
608x768: no errors
616x776: no errors
624x784: no errors
632x792:: no errors
640x800: no errors
648x808: no errors
656x816: 11 errors, 34 good images
664x824: no errors
672x832: no errors
680x840: 27 errors, 18 good images
688x848: 8 errors, 37 good images
704x864: 11 errors, 34 good images
704x872: 31 errors, 14 good images
712x872: 22 errors, 23 good images
720x880: every image generated higher than this features multiple people and/or split screen duplications every single time
So in short, it's how the software performs. Make the image small then upscale it. Take your desired image size and divide it by 2 (or 4 for big ones) and use those numbers for the SD resolution, then when it's done generating upscale it by 2 or 4.
**It's also important to note that the software has a clear preference for either Portrait or Square images. Trying to produce a landscape orientation image (no matter the resolution) will result in weird results about 50% of the time.
