I did convert all of the Te Araroa Hiking Maps from PDFs to JPEGs so far. The original maps are 16-64MB PDFs, which take forever to load on my Android Phone. I converted them using Ghostscript and Imagemagic to jpgs similar as seen here with the following settings:
convert.exe -density 200 05_v32_Manawatu_63_69.pdf %03d.jpg
This gives me jpgs up to 4MB, which look quite nice on my phone. I'm wondering if I could make them smaller. I tried pngs, but somehow all the white borders around the maps are black on my maps.
I'm no image expert. Are there other image formats that would be suitable, like a reduced color gif? If you want to give it a try, the smallest set of Te Araroa maps are the Manawatu maps with 16MB, which can be found here.