Add an export as greyscale setting similar to the option to preserve the alpha channel (which creates one if the image is exported in a compatible format).
Allow the PNG compression level to be set. As is, it's defaulted to a rather bloated level (guessing around 4) and an overnight batch filter can easily lead to 1GB+ in unnecessarily wasted space, as PNG compression is practically lossless between 0 and 9.
As someone who translates doujins as a side gig and uses Cupscale to quickly clean up images suffering from heavy jpg compression, it is kind of a pain to have to open every image, convert them to greyscale, and re-export them before I can properly work on them as they further bloat the size of project files. An unscaled image around 1000x800 that's exported at 10MB usually winds up at 1.5-to-2MB at the least. Ones upscaled by 4x comes out around 30MB, but after higher compression, ends up at about 6MB.
Mainly two
As someone who translates doujins as a side gig and uses Cupscale to quickly clean up images suffering from heavy jpg compression, it is kind of a pain to have to open every image, convert them to greyscale, and re-export them before I can properly work on them as they further bloat the size of project files. An unscaled image around 1000x800 that's exported at 10MB usually winds up at 1.5-to-2MB at the least. Ones upscaled by 4x comes out around 30MB, but after higher compression, ends up at about 6MB.