Epson SC 7900 Resolution

[Othmar.Ortner]

Hey there,
I have had a used Epson 7900 for a while now and have been very pleased with the results i got from it. The usual clogging issues got fixed very well by cleaning the wiper blade and now it works flawlessly. My main problem now is that the resolution of the prints seems to be off. Overall the resolution is solid but the printer seems to kind of "skip" lines on an image. This skipping varies greatly with software. When i downsize the image in Photoshop and print it from that program the output is absolute garbage. The whole image just doesn´t seem sharp at all and is full of missing lines. It is a lot better when printing directly from C1 but I still have weird double contours on horizontal lines as seen in the photo.



The original file obviously doesn´t have these lines as can be seen here:



And the full image so you can get a better understanding of how tiny the crop is.



The print is A4 so this is obviously a very extreme crop and the artifacts are absolutely unnoticable from anything further than 15cm (6") away. I fully understand that an A4 print has way less resolution than a 45mpix file, my problem is just the appearance of those white lines because I don´t know where they come from. Are they just showing me the limits of the printers resolution or is there something wrong with my head alignment(?) that I can fix or is there something wrong with my software or the driver (which would be implicated by different software giving me different levels of missing lines)?

I am looking forward very much to your answers!
Othmar

[degrub]

Are you using the Epson driver ?
What pixel per inch are you feeding the driver ?
It’s been a while since i had an epson, but what i remember is using something around 360 ppi. for any size of image. The driver documentation should have the preferred value so the printer’s dithering works.

[Lessbones]

It looks like you need to perform a head alignment.  A way to double check would be to print it unidirectionally and see if you get the same issue, but it looks like misalignment.

[Stephen G]

Maybe head alignment. Looks to me like the platen gap is set too wide. If your other paper settings, Paper Thickness in particular, are correct then make sure Platen Gap is set to 'Auto'. The only circumstance I can think of for setting PG to something other than Auto is when you are using media with a very uneven surface that causes head strikes.

I think of PG as a focus adjustment. When it is too wide then you get a slight de-focus along the direction of head travel. Hence the double image I'm seeing in your attached pics.

[Othmar.Ortner]

Thanks for your replies so far! Yes, I am using the epson driver. I don´t really know what resolution C1 uses for output when printing directly with it but it works a lot better than the 300 DPI that i used when printing from Photoshop or Affinity Photo. I will give printing from photoshop but with 360DPI a try.

Thanks for the ideas of changing the platen gap. There is no auto selection on this printer for it. All I can do is either narrow, standard, wide, very wide. It is currently set to standard. I will also try setting it to narrow.

One person also brought up doing a head alignment? What do I need to do for this? Would I need the special epson software for that or can i do that inside the printer itself?

Thank you very much already for all your answers!

By the way: The nozzle check pattern looks pretty clean. I added a photo of it.



And here with more magnification



Thank you all very much again for your answers! Really looking forward to solving this issue!

EDIT:

Did some tests now: Head alignment didn´t change anything BUT I tried turning bidirectional printin off and suddenly the resolution improved by an impressive amount. Everything is perfectly sharp now. Is this just a downside of bidirectional printing or is this something i can fix?

[rasworth]

Head alignment is part of the maintenance panel, and it will compensate for dual direction printing.  However, dual direction alignment is limited by paper gap, so for anything I care about I select single direction.  I would perform the alignment on a glossy or lustre photo stock, unless it specifically calls for plain paper.

Richard Southworth

[rasworth]

As I think about your problem further, dual direction issues normally show up as horizontal smearing, not vertical, the ink droplets striking the paper in one direction don't line up with those laid down in the opposite direction.  I would still go thru the head alignment process, but it's not obvious what else is going on.

Richard Southworth

[Othmar.Ortner]

I think head alignment may be the problem. I did the alignment with plain paper. Will try with normal photo paper tomorrow. Just to clarify.. The paper gets pulled in in portrait format, not landscape format. So the lines are being printed orthagonal to the direction of printing, not parallel so the smearing is indeed horizontal if you take into account how it gets printed! Thanks a lot for your help so far, will report back tomorrow morning (it is 10:38pm here right now)

EDIT:
Just did another head adjustment on photo paper for all colours. Still got the same artifact. With bi directional printing it is there, with just one direction of printing it isn´t so i am pretty sure it has to do with bi directional printing. Is there any way i can fix this? Bi directional print head adjustment sadly didn´t do the trick.

[Stephen G]

I downloaded the 7900 driver and there is a an option for 'Auto'. Just make sure that you have chosen the Media Type correctly, and that the paper thickness is correct too. Then Platen Gap Auto should set the platen gap correctly.

BUT...

Another very strange thing that I have seen with my Epson P9000 is this: when printing on Epson Premium Luster 260g rolls I get great print sharpness. Everything is set correctly in the driver, and prints come out as expected. When I try and print on sheets of the same paper I get a blur / double image similar to what you are seeing. Again: all driver settings are correct. My work around was to load a sheet, then change the paper setting on the printer to 'Roll No cut' and print from the driver as if I was printing to a roll. Then the sheet prints came out sharp.

Not the same printer as your 7900, but the Epson drivers are very similar from machine to machine so perhaps it is worth testing this on your 7900

[rasworth]

Do a timing comparison on a small print, between single direction and dual direction modes.  You may find it's not as different as you would expect, the head returns faster for single direction printing.  I'll guess you won't find many people (anybody?) using dual direction for quality printing, good alignment is inherently limited to one platen gap, I think.

Richard Southworth

[Othmar.Ortner]

Do a timing comparison on a small print, between single direction and dual direction modes.  You may find it's not as different as you would expect, the head returns faster for single direction printing.  I'll guess you won't find many people (anybody?) using dual direction for quality printing, good alignment is inherently limited to one platen gap, I think.

Richard Southworth

Yeah I agree with you. I think it takes maybe 50% more time to print but if the resolution is that much better and i can get actually sharp prints I don´t mind at all! And as I said, everything works perfectly with one printing direction. Thank you all very much for your inputs!

[Lessbones]

It looks like there may be more than one problem here--  on what paper mode are you printing?  The dots look huge in that closeup of the unidirectional print, almost like it's set on a "draft" mode or set to print on "plain paper".

Generally the rule of thumb for setting platen gap is to use the smallest gap possible before you get head strikes-- this will always improve things a little bit, but something is definitely wrong with the data being sent to the printer, in addition to the bidirectional misalignment.  I would try to solve that issue first...

When you're doing a head alignment, there should be an auto and a manual mode (or maybe the manual mode is only in the service menu?  I can't remember for the x900 series)  You'll usually be able to get slightly better results with a manual adjustment, but the auto alignment is usually very good.  Something in your processing chain is downsampling the image significantly IMO.

[JRSmit]

The problem of miss alignment can be in the feed direction as well as in the head movement direction.
Head alignment to be done after feed alignment.
Use the paper you want to print on, not a piece of plain paper.
Select the needed media type, set the thickness to the paper thickness rounded up as your printer has thickness steps of 0.1mm. Set the platen gap to Std or Wide(fine art matte papers).
For feed alignment print an image of known height (size in feed direction) , say 20cm, and measure the printed height. Use feed offset to correct. Feed offset is in very small percentage step, so the number can be easily  2 digits.
When correct, do head alignment. If you want to use auto alignment, you must use a smooth matte fine art
paper, not any gloss paper. If gloss paper is used, you must use manual.
If all done well, the difference between bi-dir and uni-dir is minimal if any.
Success

[Othmar.Ortner]

Thank you all very much for staying with me. You are really helping a lot - I already thought that I would have to live with just printing unidirectionally but now I got bidirectional printing working!

My miss alignment problem seems to have been with the paper feed. I did a paper feed adjustment earlier with a cheap glossy photo paper and now the bidirectional printing works flawlessly and everything is perfectly sharp with that paper.

After that I tried printing with Hahnemühle FineArtBaryta and the same paper options as the cheap glossy paper and it worked perfectly again apart from one problem. I took a different test image this time and now i get a weird artifact in transitions.

This is how it looks on the cheap glossy paper:



And this is how it looks on Hahnemühle paper:



Regarding overall droplet size. The whole image is about 18mm or 0.7" wide so that´s why they look gigantic. Droplet size on the print is roughly 0.025mm or 1 thou. I just made a very close up to show the separating lines properly. The printing resolution is set to the maximum 2880*1440 DPI that the printer can do. The two photos above were printed from exactly the same file with exactly the same paper profile (Hahnemühle profile) applied and the exact same settings.

EDIT: Oh sorry I forgot to mention. The numbers are there because I was saving paper and I overprinted a tiny piece of the feed adjustment print that was used earlier for manual feed adjustment.

[Lessbones]

Sounds like in that case you've pretty much got it dialed in as far as the hardware is concerned, now it's time to focus on making custom ICC profiles, or at least selecting the proper ones from the manufacturer for your specific paper types--