Digital BW, The Print

Given reports that some here have seen banding in the black when printing 
with OPM but not when printing with the Epson driver, I did a test using the 
files I uploaded earlier: The black-only profile and the 26-patch test scale.




Here is the methodology, so that others may do the same and we can then 
compare notes:

- Before you start, check that nozzle checks are clean, that the black cart isn't 
on its last legs and that the black is the MK (matte black).

- Open the 26-step scale in OPM, making sure gamma=1.8, and load the 
profile 22_OEM.MK_EAM_K_only_03L01 (as uploaded here)

- Load a sheet of EAM (EEM probably OK as long as you use the same for 
both tests) and hit Print.

- Reload the same sheet after measuring where you want the next scale to fall 
under the first one (like an inch or so below)

- Open the same 26-step scale in Photoshop (6 or 7), after you make sure the 
2200 is active in the Chooser (these tests assume Mac OS 8 or 9). 

-Set the Epson driver for Black ink only,  media=Enhanced Matte. 
Under advanced: photo1440dpi, edge smoothing=ON, gamma=1.8, 
mode = automatic, 0 brightness 0 contrast.

- In the Photoshop Print Options, under Color management, choose document 
as the source space (it will recognize that gamma 2.2 is embedded), and 
"same as source" for the Print Space.

- Still in Print Options, type the top distance your measured earlier (perhaps 
1") so that the scale will print nicely below your previous print (uncheck 
"center" of course).

- Make the print.

- You should now have two prints on the same sheet, one above the other, 
showing you how your 2200 Epson handles black ink printing with the two 
different drivers. 

--------------------------------------

Here are my initial observations:

- I saw a slight horizontal herringbone in the Epson-driver print that was NOT 
there in the OPM print. You woudn't call it "banding", but it was certainly there 
under a mild loupe. It was most prominent in the midtones and dissapeared at 
each end.

- neither print showed banding in the 100% black

- The 100% black in the Epson print measured 1.72, while the OPM black was 
1.68. In return, the OPM print exhibited perfectly linear transitions from black to 
white, while the Epson print had a huge dip into darkness from 50% all the 
way up to 100%.
 It nearly matched the OPM print from 50 to 0%. When plotted, the shape of the 
Epson print made no sense - it was just one big dive after a smooth section in 
the first half of the curve , not just a different overall shape.

- Keeping in mind that neither software was designed to make black-only 
prints of "photographic quality", this test lets you see the dither choices 
between the two drivers by exaggerating them . In a normal print you woudn't 
see as much (and, btw, I haven't tried the other options in the Epson driver):

    > The Epson driver is extremely smooth in the highlights (0-30%), then gets 
very noisy around 50-60%, then, of course.... there isn't much else but black, 
so no dither to speak of.

    > The OPM rendering is very choppy in the highlights and looks "noisy" next 
to the Epson, but then it becomes ultra-smooth, especially from the midtones 
on into the deepest of shadows.

The conclusion from this can be that the Epson driver is optimized for 
delivering fine, smooth color dots in the lower percentages (highlights), which 
makes sense for a "color printer".  OPM, on the other hand, is made with 
multiple grays in mind and the only visible highlight dots are likely to occur 
with a light gray ink, for a very short stretch of the scale (perhaps 0-5%), 
before that ink is used in higher percentages to cover the remaining 
highlights. IOW, by the time it hits the 10 or 20% mark on the grayscale, that 
gray ink is using the smooth part of the OPM dither, since it hits the equivalent 
of a mid-tone dot. Therefore, for partitioned gray inks, OPM will perform better 
than the Epson driver.

It is useful to keep in mind that comparisons between scales should be for the 
same density, not simply the same patch number. Patches between the 2 
prints match pretty well in the highlights. By 60%, the difference in density is 
small: .74 for the OPM print, .78 for the Epson print. Below 60%, the 
comparisons are meanigless since the two scales differ so much.

Again, bear in mind, that this is just a test aimed at revealing differences that 
would be hidden in a normally profiled print. The purpose is only to isolate a 
single jet and see its behaviour - either for troubleshooting or to compare 
other driver behaviours. Those with access to IJC can of course do this for 
each of their jets, which is a good way to isolate banding and other problems 
that a composite scale or just nozzle checks will never show.

Antonis

Antonis,

Thanks for the black-only profile, the 26-patch, and the methodology.

I just finished my tests and my observations are somewhat different, but 
before I get into that, I want you to know that I emailed a scan of my OPM 
problems to Charles at BowHaus.  He sees what I am encountering and they are 
going to try to reproduce the problems.  Hopefully they will solve it.

OK, now to my tests using your methods.  

1.  Using the OPM black-only profile, I still get banding in the 100% patch.  
My thinking is that if it's ink starvation, a faulty black cartridge, or a 
bad black head, I would be seeing banding throughout your 26-step patch.  Do 
you agree?

2.  Using black-only with the Epson driver, no banding.

My visual observations are somewhat different than yours:

1.  You see a herringbone pattern in the Epson driver; I do not.

2.  My Epson driver has a nice long tonal scale, unlike yours which dips into 
dark from 50-100.  Like yours, the dots are most apparent in the midtones.

3.  The OPM driver is more compressed.  From 0 to 44, I see white striations 
in the top part of the scale.  I see these with my eye but cannot see them 
under a loupe.  Patches 68-84 seem to be the same tone.  OPM's midtone dots 
are less apparent than Epson's.

I will put everything under a densitometer later today or tomorrow and let 
you know.

Helene

> Given reports that some here have seen banding in the black when printing 
> with OPM but not when printing with the Epson driver, I did a test using 
> the 
> files I uploaded earlier: The black-only profile and the 26-patch test 
> scale.
> 
> 
> 
> 
> Here is the methodology, so that others may do the same and we can then 
> compare notes:



[Non-text portions of this message have been removed]

Helene,

glad to see you ran the test, so we can compare notes. Some of mine to follow 
yours:


> 1.  Using the OPM black-only profile, I still get banding in the 100% patch.  
> My thinking is that if it's ink starvation, a faulty black cartridge, or a 
> bad black head, I would be seeing banding throughout your 26-step patch.  
Do 
> you agree?

Yes, that seems logical.... The mystery, of course, is that I don't see that 
behaviour on _my_ 2200. So it remains worth exploring further....


 
> 1.  You see a herringbone pattern in the Epson driver; I do not.

That may well be differences in head alignment (since presumably you are 
using the exact same Epson driver settings). I should re-visit that procedure 
on my printer, perhaps.




> 
> 2.  My Epson driver has a nice long tonal scale, unlike yours which dips into 
> dark from 50-100.  Like yours, the dots are most apparent in the midtones.


Hmm.... that makes no sense: we should be getting identical density results for 
identical driver settings. Do you mind double-checking that your page setup  
and other print settings in PS were the exact same as mine?
As for the dots themselves, we are in agreement.


> 
> 3.  The OPM driver is more compressed.  From 0 to 44, I see white striations 
> in the top part of the scale.  I see these with my eye but cannot see them 
> under a loupe.

We see the same there. The highlight dots are too scattered up close to see 
the striations under a loupe. The "top" part of the scale, presumably means the 
continuous gray ramp that appears above the individual patches as they are 
laid out horizontally. 

I don't know if these breaks or "striations" are a result of the particular profile, 
though. I didn't spend time exploring that further. I just made sure the patches 
came in at the proper densities. Tiny moves in the profile may make a big 
difference here, don't  know....




 OPM's midtone dots 
> are less apparent than Epson's.

We agree on that too.  Hence my conclusion that in a real bw print situation, 
it's the mid tone dot that matters most for partitioned gray inks.


Interesting comparisons.... thanks for reporting back.


Antonis