I don't think pen table files will affect shaded views. You might have some luck with Ghostview. In the convert menu there is a properties dialog box. There are all kinds of properties you can set about down sampling color images and gray images. I poked around a bit but did not find anything that worked for me in a couple of tries.
There is also a pcxgray device that sounds like it's gray scale but I don't have a PCX file viewer.
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