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I have the hex kit desktop app from the kickstarter but all the maps I make are way too big file sizes to upload to roll20 as an image. Is there anyway to export the maps to roll20 or do I need to use the roll20 version of hexkit
I'm not familiar with roll20 specifically (I know what it is, but have never used it) but I would imagine that you should be able to reduce the file size considerably by exporting the map to a standard graphics format, then using gimp or another image editor to re-save it with different compression settings.
Just remember to start with the original exported image each time if you need to do this repeatedly (e.g., to find the optimal compression settings) or else you'll get reduced image quality (and probably increased file size) as the compression artifacts accumulate.
I have to take the images into something like Photoshop, Fireworks, etc and optimize it so that it meets the filesize requirements (I am at the top tier paid account on Roll20).
For your information, here is Roll20's wiki on Images: https://wiki.roll20.net/Image_Best_Practices_for_Roll20
The latest version of the app available on Itch gives an "Export Digital" option, which should be useful for uploading to Roll20.
While getting a basic level of competence with a paint program such as Gimp or Photoshop is a good idea if working with Roll20 or other VTT programs, there are other apps that can also do a lot for you without so much of a learning curve.
IrfanView is a very handy image viewer with excellent image manipulation capabilities as well. You can scale, crop, rotate, tweak color and a number of other functions in a lightweight app. When I get a new PC, it is one of the first programs to get installed.
As Ross said, the new Export Digital option puts out a ~77 pixels/hex image that is more suitable for VTT use. If you want a specific pixel/hex setting you can take the full size image and scale it down to the desired size in IrfanView or pretty much image manipulation program.