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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.