I am looking to produce the highest quality prints possible on an HP
Color LaserJet 4500N. The printer is connected via a network (not
directly from my PC).

The files I want to print are natively in Photoshop format (*.psd) and
I work in Windows. The files are quite large (25-35 mb). The images
are more graphic than photographic in nature, with solid colors and
engraving-like lines (rather than photographic images). Overall, lines
need to be very crisp, colors solid, contrast true. There's not much
contiuous tone in the image.

The problem (it seems) is that the printer lowers the resolution of
the image. It looks like the image is dithered in the final outputted
image.

To test this theory, I printed a small portion of the full image, and
compared it with the full image. It seemed that the image quality of
small portion of the image was much better than the image quality of
the full image. Lines were crisper, colors were truer and brighter,
and it appears there is less dithering.

The differences are slight, but important, and it seems clear that the
printer is printing a lower resolution output of the image with the
larger file size.

I tried adding RAM to the printer, but this had no effect.

Could it be that connecting through the printer via a network would
make the printer printer at a lower resolution? Would it print better
if the PC were directly connected to the printer.

Also, I have tried adjusting the printer settings in Photoshop, and in
the HP print software, without much effect.

Would a printing-to-file approach help? If so, how is this done?

Please provide specific steps. I am familiar with Photoshop, but have
very little experience in working with printers and printed output.

Thanks.

When hearing from users that the quality of the output is in question,
the most common solution is choose the closest paper setting that
represents the actual paper you are printing own. If your paper is a
gloss then choose the media setting of "gloss" (if you do not have
this ability then perhaps you are not using the correct driver for the
device).

These media settings are included with the "driver" of the printer and
are optimized for most common types of everyday printing, sometimes
regarded as "pleasing color"

There are other settings that may effect your output, for example:

Are you using the most up to date driver for the printer?  Go to HP's
website and download the current version if in doubt.

There are other settings that allow you to overide the "Color Smart"
mode and go into "manual mode" and choose a mode that is optimized for
photos or drawings, but sometimes the results can be dubious compared
to the "defaults".

The difference in the appearance of the cropped sample and the full
sample, i suspect, has more to do with a difference in ones mind that
one may or may not expect. What i mean is i have experienced the same
feeling when performing the same kind of test and i have determined
that unless its a technical error of some kind (used different print
settings for each print or scaled verisons of the samples) then its
more like what i like characterize as an "optical contusion".

RAM only really helps the printer store/process more information
rather then depending on the host computer to store/process
information, which in turn relieves the host computer sooner so other
tasks can be begun. So this is not a loss but an unintended benefit.

Printing to the printer in a different connection type would only
change the speed of the data getting to the printer, it would not have
any effect on the quality of the output, so the answer is no.

Printing to a file would not help unless you were using some type of
RIP, like a Fiery or the sort and still those products would be
limited to the feature capacity that the printer is capable of, this
answer is also a no.

Good luck to you.