[cups] Epson WF-6090: Varying line thickness on prints with horizontal lines

[David Rea]

Hello-

When printing pages with thin horizontal lines from my Linux box, I see
visible variations in the thickness of the lines from top to bottom:

https://photos.app.goo.gl/6j799q2Sny2kx9RM9

Running an Epson WF-6090 inkjet set up on my Ubuntu 16.04 workstation
running CUPS 2.1.3 and a PPD file downloaded via Epson's
website: epson-inkjet-printer-escpr 1.6.20-1lsb3.2.

The output file is a PDF, generated by PDFkit. The horizontal line
thickness is uniformly 0.1mm, or 0.283465 PDF pixels. The only resolution
option in the printer's settings dialog is 300DPI, and the same visible
variations occur when I round the line thickness to the nearest 1/300th of
an inch (0.35 PDF pixels).

Printing either file from Adobe Reader on Windows 7, using Epson-supplied
drivers, results in uniform visible thickness:

https://photos.app.goo.gl/MfKauNQ3Qjffek688

I've tried varying paper and quality settings, running from the generic
inkjet PPDs, and printing from both Chrome and evince under Ubuntu (all
"scale" and "fit" options disabled, in both cases), all with identical
results. Something appears to be resampling the PDF, possibly during
rasterization?

Any assistance with this issue or guidance on further troubleshooting would
be greatly appreciated!

Thanks,
Dave