Thanks for the input.
As noted earlier, I generate my images using Daz Studio as 3d software (sometimes using Cararra for landscapes or Hexagon for model editing, and in one case I used a "comp" photo as a background). I use a Daz Studio plugin called pwToon to get the outlines, but for some elements, e.g. hair and eyes, I use pwSketch, because I like the way it looks better. (pwToon provides nice configurable outlines, and can do shading as zip tones, but doesn't convert color or patterns to b&w. pwSketch does, but doesn't do fixed-width outlines.)
Then I import the PNG files into Manga Studio, after setting up the panels. Manga Studio can convert to grayscale or can convert to screentone-- it doesn't handle colored image import (not that I want color for this anyway). I've been using the screentone setting, which I think is making the outlines a bit grainy. I also set this project up at 300dpi, which I think was an error. I thought it would be plenty given that I'd only be using 72 dpi in the screen version, but the way Manga Studio converts to screentones introduces a lot of pixelation, even though I have screentones set to 85 lines (the maximum). From Manga Studio I output JPG files at 300 dpi. The result is what you see in my gallery here at MR... except that MR automatically reduces file size and so I may be losing some image definition there. At Artzone I'm restricted in filesize, so I manually reduce the JPG file dimensions, usually with Fireworks.
Things I'm thinking of trying:
a - converting the various color/pattern files ("textures") to b&w screentone patterns and then applying them in Daz Studio, and importing the resulting rendered images to Manga Studio with minimal image conversion-- this should greatly improve the crispness of the outlines.
b - Importing the images to Manga Studio as grayscale, rather than converting to tone. I don't know how this would look in print, but it would probably look a lot better on the screen, as screentones actually don't display well at 72 dpi.
c - Either way, I might redo the existing pages at 600 dpi, though that would generate some really huge JPG files, and I wouldn't be able to post them at MR or AZ at that file size.
I may post a couple of examples of my image conversion experiments in this area. I'd love to get comments about which results look best to folks when viewing online. The odds of printing ever being much of a concern for this title are pretty low, after all.