Premium VTT Maps Seem to Large to Use

Can these maps work on Roll20? I have a Heroic Maps jpg that won't load, for example.

Heroic maps are huge, intended to print at 300dpi (not necessary at all for the intended print method, but that's just my printing history speaking). You will need to seriously downsample them. Most graphics programs can handle this. The maps are beautiful, but way too big for VTT. I typically take them from 300 dpi to 70 dpi (to match the chosen scale of Roll20). This should on average, reduce the number of pixels to 300^2 / 70^2 or about 5%. Save as jpg. Their maps are typically so noisy (not a disparaging term--just means a lot of variation and detail from area to area) that you can get away with a good amount of compression. I typically set a quality of 3-5 (or 30-50, depending on your software), and they look fine. For anyone who is interested, the "300dpi rule" you so often see requested comes from requirements for typical 4 color offset printing, which almost no one would use in this case. You are far more likely to be using some form of desktop or on-demand printing, which does not use 150 line halftone screens. Which is where 300 dpi (4 pixels per hafltone dot) comes from. Annoys the heck out of me because people believe it to be some kind of magical quality number.

Yeah, we use 300 DPI for our art and maps at work.  Thanks! Got it to work with Paintbrush and sizing at 25%.

I use Photoshop for my freelance business, but anything from the Gimp to  Preview should work. Technically, you don't even need an app. You could automate the resize with Automator or Applescript using Image Events. What work do you do that requires art and maps? I work at the local newspaper where I do have to deal with halftone line screens. :)

keithcurtis said: For anyone who is interested, the "300dpi rule" you so often see requested comes from requirements for typical 4 color offset printing, which almost no one would use in this case. You are far more likely to be using some form of desktop or on-demand printing, which does not use 150 line halftone screens. Which is where 300 dpi (4 pixels per hafltone dot) comes from. Annoys the heck out of me because people believe it to be some kind of magical quality number. Amen to that. And you hardly ever need 300 dpi (or ppi, to use the correct term… but even Adobe is now using dpi) for normal offset printing either. The correct formula would be "line frequency ⨉ 1.41" - for 150 lpi you're totally fine with 212 dpi. But because it's rather complicated to calculate that in your head, people multiply by 2 instead – this is where the "300" originally came from.  I've been arguing about this so many times in my life, especially with so-called "print experts" working at newspaper printers (where even 150 dpi are more than enough). But back on-topic: I can only agree to what keithcurtis said. 70 dpi and saved as JPG should do the trick. I personally use Affinity tools to draw my maps... and I can only recommend them as alternative to Illustrator, Photoshop and Co.

I have been using a spreadsheet called  mapscaletool since my days of using Maptools. It allows you to enter the overall image size, the number of squares on the image, and the desired DPI per squara; I set my squares to 72 dpi. It then calculates the precise scale and image size to convert your images to using Gimp (free) or Photoshop. There's also a few videos showing how to use it online if I remember correctly.

Bless you, Arthur B.