QTR + MIS Carbon inks: Banding-Free Gradients ?

[Ken Lee]

I've been trying to print some photos which contain large smooth gradients in out-of-focus areas.

Using the available QTR tools to make profiles (including linearizing tools provided by Richard Boutwell) I have been unable to make prints whose gradients are truly smooth. The banding is not blatant, but present enough to spoil the image, especially on large prints.

I suspect this is because measuring only 21 steps is an inadequate approach. Also, my consumer-grade Spyder spectrophotometer gives me imprecise and varying readings: I have to average them out.

Prints of ordinary subjects look perfect. This problem only appears in images which contain substantial gradients. This isn't about print head alignment or cleaning cycles, this is about the quality of the profile.

Somewhere I read that Piezography profiles are custom-linearized to exceed the imprecision inherent with ordinary QTR tools. This might explain why they are available for only a limited selection of papers.

Has anyone printed out any gradients using Piezography inks ? Is there banding ? I mean, any banding at all ?

Better still, are there other ways to get a truly linearized profile ? I mean... linear.

Here's a 16-bit Grayscale TIFF file which reveals banding when present: http://www.kennethleegallery.com/ima...BullsEye51.tif. It combines both a continuous gradient and 51-step wedge as a Bull's eye.

[Peter De Smidt]

You might try adding a bit of monochromatic Gaussian noise to the areas where banding occurs, just enough to eliminate the banding but not be visible otherwise.

[Ken Lee]

You might try adding a bit of monochromatic Gaussian noise to the areas where banding occurs, just enough to eliminate the banding but not be visible otherwise.

I want the print to look smooth, just as the image looks smooth on my calibrated monitor.

It's ironic that the QTR allows us to print in 16-bit mode, but (if I understand correctly) the actual profiles contain a lookup table of only 256 values (8-bit).

Meanwhile, if we measure only 21 steps, that's less than 5-bit precision. Am I missing something ? Is the rest handled with interpolation ? If so, is that really 16 bits ?

[Peter De Smidt]

With the right amount of noise, the image should still look smooth. I don't know the answers to the QTR questions. You might ask Roy.

[WalkerBlackwell]

There is no banding with Piezography inks. Partly its in the ink chemistry, partly in how we build the ink overlaps for the .quads that are built for Piezography, and partly its how we linearize.

All together, these three markers make perfectly smooth prints that exceed every other monochromatic system (besides maybe our most recent PiezoDN dig-neg system).

best,
Walker

[Ken Lee]

Here's a photo made with a portrait lens. In the negative and scanned image viewed on the monitor, there is a smooth halo around each of the flowers. On my QTR print, the halos have 3 bands.



Are you suggesting that I add Gaussian Noise to the whole photo, or just the halos ? Would I paint it in using a mask ? There are a lot of gradients to deal with.

[WalkerBlackwell]

Adding noise essentially negates the qualities of dedicated monochrome ink systems (my opinion only).

You might as well go with K3 at that point as this is essentially what K3 does (by spacing the dots of darker ink to make lighter tones) to mask defects in the linearization (or media-types).

When properly profiled, a qtr Piezography K6 or K7 print has significantly more resolution and fidelity than either K3 or a noised image . . . that is kinda the point.

best,
Walker

[Bruce Watson]

Prints of ordinary subjects look perfect. This problem only appears in images which contain substantial gradients. This isn't about print head alignment or cleaning cycles, this is about the quality of the profile.

Yes.

Somewhere I read that Piezography profiles are custom-linearized to exceed the imprecision inherent with ordinary QTR tools. This might explain why they are available for only a limited selection of papers.

Yes again.

I think you understand the problem and the solution.

That said, I've got a number of prints using the old 4 ink system that have smooth beautiful skies that are gradient city without a trace of banding. But as has been pointed out, this was done using some artful dithering. The six+ ink systems are able to resolve more detail in part because they can do away with this dithering, but at the cost of harder to make profiles.

[Peter De Smidt]

Possibly try the various dithering options in QTR. This is from a long time ago, but perhaps it is relevant: http://photo.net/digital-darkroom-forum/00BR5g

It does seem to be a profile issue, and coming up with a really good one is the most difficult thing about QTR.

For adding noise, I'd start by adding it to the whole print to see if the banding goes away while not adding any roughness. Assuming it works, I'd use a luminosity mask to pick the appropriate areas, using Quick Mask to paint out any problems.

If I were you, I'd send an email to Paul Roark asking for his suggestions.

[sanking]

Ken,

There should not be any banding in printing 16-bit files with either Piezography or with any other all gray ink set with a well-designed profile. Are you using the GRAY_OVERLAP command in your profile? If not, you might want to try it as I have found this feature very important for profiles where you have 6-8 gray shades. You might ask Richard Boutwell about this, as I recall he mentioned at some time in the past and had some suggestions for setting gama values in conjunction with the GRAY-OVERLAP command.

Sandy