Who at Epson?
The printers are not 'only 8bit printers" because bit depth is an attribute of the data sent to a printer. Can the printer use more bits and provide a visible difference is the question. On the 3880, the answer is no. ...
I don't know who in Epson. I asked Mirage to investigate why I could not select 16 bit printing on the Mirage Print 4 for the Epson P800 and the answer was that Epson did not allow it. I asked them to check why with Epson and the answer that came back was (sic)
About 16-bit they wrote "The EpsonHTM for P800 is not support 16-bit." this is a clear answer especially if you take into consideration that a Japanese normally does not say "no".
Mirages response on the 3880 was "The 3880 does not support 16bit. The best it can do is 8bit. The only printers that do support 16bit are the large P-Series printers (P50xx, P60xx, P70xx P80xx etc.). In Mirage, in the "Advanced" settings, you can select "Always 16bit", but if the printer can't do it, it'll revert back to the possible bit depths. I would recommend selecting "Match printer depth", since it will give you the best possible outcome.
In March I asked a guy who used to consult for Epson and his response was
"Epson have never released a 16-bit per channel driver (half toning module) for any of their desk top printers, so 8-bits is all Mirage can pass to the printer (via the Epson half toning module that Mirage uses to do the RGB to CMYK+ conversion). Perhaps the just announced P900 replacement for the P800 may have a half toning module that can pass 16-bits to the print heads, but we haven't tested the P900 as yet so don't know. In any case, it is only very smooth gradients that usually benefit from more than 8-bits of data. That is, it is often hard to see any difference (with all other things being the same - dithering pattern etc.) between a 16-bit file printed through an 8-bit print path compared to a 16-bit print path."
An extreme test is to create a 16-bit per channel RGB gradient at 360ppi in Photoshop from 0RGB to 255RGB with No Dithering and print it through an 8-bit print path (such as the P800 half toning module in Mirage), and see if you can detect any stepping. The print will need to be large enough for the steps to be physically distanced enough that it can be seen - 256mm wide will ensure each step in 8-bits is around 1.0mm, which will be easily visible to the unaided eye. If the result is not smooth enough for you, and you print images containing artificial gradients all the time (or many wide angle blue skies etc.), you'll then need to add some noise (i.e. dithering) to your files to help disguise the banding. Of course the above assumes you are using an incredibly accurate profile based on a highly smoothed (i.e corrected) data set, which unfortunately most printer profiles we see and test (but not our own) are anything but smooth and internally consistent and consequently banding can be visible in such an extreme test, but it is due in all the cases we have seen to the poor quality printer profile more so than the 8-bit print path.
