#578 Mitsubishi K60 - Artefacts in white areas
Hey,
First off - really appreciate the work that's gone into getting these sub dye printers working, thanks!
I've got artefacts showing in areas with a very (very) slight change in white tone's, best shown by the attachments. ('Fine', 'UltraFine', then a copy printed directly from a Mac using official drivers, on UltraFine - All are Gloss & I wouldn't call any of the outputs blurry, that's my camerawork under yellowish LED lighting)
I'm running 5.3.4 (Colour fix's have worked wonders!).
I've tried most printer setting combo's.
The only thing that lessens the artefacts, is printing in Fine, instead of UltraFine, this doesn't help the rest of the colours though.
Really not sure where to look, hopeing someone tell's me to flick a button and all will be well!
Cheers,
Mark
It's worth me saying - there are just visible yellowish artefacts on the Mac-printed image.
Also - this is only occuring after what I assume are dodgy jpeg compressions?
Printing photo's with large close-to-white areas, doesn't cause this.
Last edit: Mark Howe 2020-02-05
That you got this far tells me you found, compiled, and installed the image processing library. If you could confirm what version you're using, just for my own sanity?
And, did you enable use of the "3D LUT" (defaults On with Gutenprint, IIRC) or are you using an ICC profile as part of your printing flow?
(the 3D LUT is better than no correction, but the ICC gives consistently the best results. I don't know what the default OSX driver behaviour is..)
That said, this image processing code is the result of a significant (and sanity-questioning) reverse-engineering effort, and it's certainly possible there are still bugs lurking in its bowels. This image might be triggering some particularly pathological corner case.
So, I was able to reproduce this on my
Kodak 305 (aka rebadged Mitsu K60).
I do all my printing in Ultrafine mode with the ICC profile, and the artifacting is faint but still there.
(as an aside, enabling both the LUT and ICC profile makes the artifact slightly worse)
Unfortunately I'm not sure what I'm going to be able to do about this in the short term. I don't have the ability to do side-by-side intermediate comparisons of my code vs Mitsubishi's, which will really slow this effort down.
Oh, one other thing you could try -- sharpening settings. Dial them down (or turn it off entirely) and that might make a difference.
lib70x was on there, I've just pulled down the latest from your git (0.7.2?) - similar results.
Printing's straight from the cli, headless on a rPi 3; lp img.jpg
No ICC in use for the first tests (Since tested with a cupsICCProfile ../Default: line in the cups Mitsubishi-K60.ppd - no difference)
Not sure where I'm looking for the 3D LUT;
I've tried with/without Internal Color Correction
Also tried with/without Linear Contrast Adjustment
Tried a fair few of the 'Color Correction' settings, Uncorrected / High Accuracy doesn't make any difference to the issue.
Turning sharpening way down blur's everything, including the artifacts.
The joys of closed source! I've seen your attempts at getting help out of the, maybe 2020's the year!
Looks like they're toying with releasing Linux drivers, nothing on there for the K60 though! http://www.mitsubishi-photo.cz/drivers/drivers_printers/cz_en/drivers_printers_digi_en.htm
Something's triggering it to care about colour a little too much, if that's a thing.
Across the entire background of this image, outside of the big artifacts, the white area is is #ffffff with single pixel's of #fefefe. While practically the same colour on a screen, my prints have light grey dots in all these spots (with shapening on 4, I'd say they're there but blurred with sharpening on 1)
I have other images with black text on an fff background, the image library leaves off-whites around the text, these also show on the prints as a light grey ghosting.
You'll probably shudder at the thought of a test image photo, but I've attached one.
The blacks bottom-left are all distinguishable, apart from furthest left
The greys bottom-right however, are all very visible, it's as though it doens't know what to do with light greys :(
Don't want you to pour too much into this, I can print from the mac, I just had dreams of this working. Anything I've missed, or I can do to help / test, reach out. Appreciate everything you've done on this!
I've found and fixed two minor logic errors in the library, but neither change has any effect on the artifacts in that first image you posted.
This makes me thing there's something else going on -- maybe rounding/truncation errors due to implicit integer<->floating point conversions. Another possibility is that the color issues are due to Gutenprint's internal conversions, and the library is dutifully passing it along.
BTW, you'll definitely do a little better color-wise if you are using an ICC-aware workflow, and apply the correct ICC profile (there are separate ones for Fine and Ultrafine)
I think I've found the problem. Now when printing that image, the artifact/shadow is just an um, shadow of its former self. It' s not completely gone, but that's because the original image has that slightly-not-white shadow in it.
(you'll need to grab and compile the latest backend and library code out of my selphy_print repository...)
At this point I think any remaining difference between the Mac and Gutenprint can be attributed to slightly different deault contrast/brightness/saturation settings. Your mileage may vary, of course.
(For the record, I'm now up to five logic bugs identified and fixed. What a PITA..)
Your guesses sounds much more educated than mine!
Things are still weird on my end unfortunately.
I've compiled fresh copies - gutenprint-5.3.4-2020-02-13T and a pull of your selphy_print master branch.
Prints were still coming out the same as my original UltraFine photo.
I've since got it showing the shadows, but without the specled grey allover the white area by applying the ICC profile (CPK60_UF_HG.icm), set gutenprint Internal Color Correction to No, and 'Color Correction' to Uncorrected (Ultrafine, ImageType photograph, everything else as default)
Setting a bad ICC on the Mac, will make it print these same clear grey artifacts, so it's pointing me to a setting somewhere.
I use the HG media, and the printer firmware was updated as such.
Looking at the official driver files, they have duplicate .cpc and .lut's. I've tried replacing the copies in /usr/share/gutenprint/backend_data, on the off chance that'd impact it, to no effect
(CPS60T01.cpc -> CPS60H01.cpc... CPS60T03.cpc -> CPS60H03.cpc... & CPS60L01.lut -> CPS60HL1.lut)
I've done the above on a Pi3 (My origional setup - icc through jpegicc), then today in an Ubuntu VM, so I could use the GUI & set the icc within the settings and print via gimp.
I must be missing something, but I'm giving up at this point, appreciate what you've put into it Solomon, really doing the devils work!
I'm going to close this. While not perfect, the output has been noticably improved. Short of putting obscene amounts of time into additional reverse-engineering, there's nothing further that can be done.