[j.p.s]

Originally Posted by JSWolf

Here you go.. hi-resolution maps for The Heroes that you can use to replace the low-res ones in the book.

http://www.joeabercrombie.com/maps-for-the-heroes/

Those are very densely detailed for line drawings, but PNG would still be a big win over JPEG, and in more than one way.

Simply converting them to PNG with 256 shades of gray made 1.7MB images, a 37% reduction. Under the bash shell.
for i in heroes-*jpg do; djpeg $i | pnmtopng > PNG0/`basename $i .jpg`.png

At the other extreme, converting to true B&W (1 bit) images resulted in 209KB 2048x1448 images, but those look significantly worse, even no counting the gray regions being shown
as white.
for i in heroes-*jpg; do djpeg $i | pnmdepth 1 | pnmtopng > PNG1b/`basename $i .jpg`.png; done

Converting to 2 bit (4 "color") PNG made 402KB full size images, less than 15% of the space required, or an over 85% reduction. The reduced number of gray shades probably slightly reduces the anti-aliasing benefits of more gray shades, but it also somewhat reduces JPEG artifacts. It even reduces scanning error. This happens all over the image, but it is most clear in areas with a single gray shade, such as the lower left and upper right corners. This makes the image cleaner and use fewer bytes.

An optimal way to produce the web images would have been to scan them at 600dp (4096x2896)i 2bit (4 color) and save them as 2048x1448 4bit PNG.

To really go all out, scan at 1 bit 1200 dpi, fill in the regions that should be gray with some tool, and save as 2048x1448 4bit PNG.