I've wasted a couple of days trying to import megascans plant assets with textures of 512x512 resolution. I expect this guide to be outdated soon, but since it's a frustration that I expect other people are dealing with, and I found a couple of useful tools along the way, I'm making a post in order to
A: save some steps for anyone else looking to import lots of Megascans assets to unreal
B: Have a handy reference for myself in the future
Bridge has a minimum export resolution of 2K textures at the moment, but this is overkill for most games applications, especially when a lot of the assets are quite small.
It's possible in unreal to set a lodbias for textures so that packaging builds use a lower resolution mip. But it means that you'll be keeping the larger textures on your repository, bloating it unnecessarily.
My quick and dirty solution was to:
1. Import the textures at 2K
2. Use a batch image resizing software, such as IrfanView (which is very lightweight and very fast) to:
a: create a backup copy of the original 2K texture
b: resize and overwrite the 2k texture with a 512x512 version
3. Re-import all the textures inside of UE4, which will now pick up the 512 version instead.
IrfanView can pick up all of the images in a directory and all of its subfolders and apply batch operations to all of them. It's a really powerful little tool.
It even allows you to export a .txt file containing the path of each image, and then you can edit and re-import the text file.
Using Notepad++ mark and bookmark tools, I was then able to use keywords to remove each path that I didn't want to IrfanView to process.
Since there were about 2000 images in total, spread throughout subfolders, and in varying resolutions. Doing this another way could have been incredibly time-consuming.
I hope that this little guide helps somebody else in my position. I'd heartily recommend that people check out IrfanView, it's very easy to get to grips with and incredibly powerful, it even has basic scriptability. Not only that, it's free for non-commercial uses, and relatively cheap for everyone else.