Current Algorithm seems to be based around Linear resize.
However when you look at other CBR's such as CDisplayex they have Lanczos implementation which is clearly superior interpolation at all zoom levels.
Suggestion 1: Add a better Scaling Algorithm.
It doesn't have to be Lanczos. It can be Spline 36/64 etc.
However there is clearly a lack of sharpness with the current algorithm compared to other implementations using the far superior interpolation.
As far as pc resources are concerned, even Laptops from 2013 have no issue scaling 4K native with Lanczos.
It really shouldn't be resource intensive at all to implement and if it is, that's what the pageflow performance tab is there for.
Suggestion 2: Auto color correction
A lot of .cbz's .rar etc are based on personal scans etc. However because most people don't know how to use a scanner, what often happens is the black point gets lifted. Scenes that should have pure blacks now have black levels starting at 50/255 which just lowers contrast for the entire image.
Yes there is an image adjustment tab. However, it has to be manually tuned per image.
Again, looking at CDisplayex's implementation. It is auto set per image. Which is a far, far better system.