Printing quality problem with HP LaserJet Pro MFP M127fn

[Zoltan MIKLOVICZ]

I have a HP LaserJet Pro MFP M127fn printer. I use it with Ubuntu 14.04 LTS and hplip-3.15.7.
I installed the printer and it works. But the printing quality is very wrong. I changed the resolution from 600 to 1200 dpi, but the result was the same.
I checked the ppd file and I found:
*OutputMode FastRes600/FastRes 600: "<</OutputType(normal)/HWResolution[600 600]>>setpagedevice"
*OutputMode FastRes1200/FastRes 1200: "<</OutputType(best)/HWResolution[600 600]>>setpagedevice"

How can I change the resolution?

[Till Kamppeter (till-kamppeter)]

To the HPLIP developers at HP: Is this intentional that both FastRes600 and FastRes1200 have 600x600 dpi as hardware resolution (HWResolutiuon)? Can one make this printer print with "/HWResolution[1200 100]"?

[Zoltan MIKLOVICZ (zmiklovicz)]

The HPLIP-3.15.9 version solved the problem.

[Till Kamppeter (till-kamppeter)]

Zoltan, can you attach the PPD file of your print queue (from /etc/cups/ppd/)?

[Zoltan MIKLOVICZ (zmiklovicz)]

I attach the ppd file.
Very interesting, the HWResolution didn't changed.

I used the hp-upgrade tool. I choose the automatic install method.
The hp-upgrade downloaded the new version of hplip, uninstalld the old one, and installed the new.

Today i changed the print quality to 600dpi, but the printer use the 1200dpi.

[Till Kamppeter (till-kamppeter)]

It seems that this printer only accepts 600-dpi raster data but has a 1200-dpi print engine. The FastRes600 probably makes a square of 4 output pixels out of each input pixel and the FastRes1200 probably does interpolation to smooth edges. To the HPLIP developers: Am I right?