I will be honest, the technical stuff you just said is beyond me (save the first sentence, that I understand what it means).
5120x2880 image pack => do you have many patrons with a 5k monitor and the rig being if I may ask, just curious, it's not common in,porn game, at least to bother with such high quality.
Well that's where the adaptive scaling comes into action.
The Ren'Py engine scales the image you give it to the game set resolution.
So for DD the game is 1280x720. That means that all images will be rendered as 720p images. If I put a 1080p image and display it it will be downscaled to 720p.
The thing thought it that downsclaling is unrelated to the current size of the window the game runs in. So if on your perfectly normal 1080p screen you maximise the game the 1080p image I put in the game will still be downscaled to 720p then upscaled to 1080p.
That leads to blurry images even since the upscaling Ren'Py does it not stellar either.
As I said ultimatly PyGame is used to render the images, and it is perfectly capable to render any image to any resolution it doesn't care about the size of the image it just pin it between the points you give it.
So what I did is rewrote that little part of Ren'Py managing the images and made it store the full image (not the one downscaled) then display it as it was a 720p. For Ren'Py it is a 720p image, so it passes it to PyGame as such.
But sine the image is still at its native resolution and PyGame doesn't care about it it renders at the size of the window.
All of that explanation to say that even if you don't have a 4K screen you can still enjoy a nice sharpness boost.
Here is a comparison on my 1080p screen with the window maximized (so less than 1080p)
The Lossless , Light and Ultralight versions are 720p images the Upscaled is 2880p.
The images are upscaled from the render which are 720p so it doesn't cost us that much computational time. There is also some quirks to the upscaler as it is AI based.
But I must say I like that AI it really seem to love collars and other BDSM gear, it always does a great job with it.
Also keep in mind that the GIF is slightly compressed too so the image appear a bit more grainy than it is in reality. It still shows well how the upscaled image is sharper even on a 1080p screen.
If you want to compare more in detail I attached each static image to this post.
The Upscaled image pack uses a lossy compression though and it is around the same size as the Lossless one and the quality drop is minimal and not really observable unless you have indeed a high resolution screen reasonably close to your eye.