Hello,
being this my first post I'd like to briefly introduce myself: my name is Davide Barranca, I'm from Italy and I mainly do post-production and digital printing for photographers involved in the contemporary art business (a strange business indeed
)
I've recently run into a peculiar problem dealing with P65+ files, more specifically developing them - I hope this one is the correct forum section: while the issue I'm reporting is about raw processing (and a couple of raw processing softwares), I suspect it may affect P65+ digital backs tout-court.
The problem is about a highly geometric non-uniformity of color rendition (especially in the green/magenta axis) - something that's generally very subdued, but that can explode when you deal with grayish images that you may want to push towards a more colorful interpretation.
There are several ways to make this deliberately happens: one particularly rude way is as follows:
1) Bring .IIQ (PhaseOne raw files) directly into Adobe Camera Raw (ACR), no matter whether CS4 or CS5 version, zeroing all the sliders, and with a decent (not necessarily perfect) white balance.
2) take them in Photoshop, it doesn't matter whether in 16bit or 8bit, sRGB or Adobe1998. Convert to Lab color mode.
3) select the "a" channel (the one that is about green/magenta opponents) and do a Image-Adjustments-Equalize command.
I've tested two different P65+ digital backs with two different Phase-One cameras and the results are always these: the colors (obviously) become a mess of green and magenta noise when I look at the composite image, BUT, if I inspect the "a" channel, it's always divided into 4 quadrants (like cartesian axis) with different weight: say, the top left is lighter, the top right more dark, the bottom left the darker, the bottom right the lightest. The effect's magnitude depends on the image (photographs of colorful object show less, let's call this "quadrant posterization", while grayish images like rocks, are clearly more offended.)
I understand that no one is using the equalize command on a Lab channel on purpose, but I assure you that if you do a couple of standard tricks in Lab to boost the colors, it's easy to end up with a picture that shows a more magentaish bottom left side and a greener bottom right one (just to let alone the top).
I've run into this issue almost always with ACR, far less with Capture One - let's say more properly that the effect is less obvious with C1 - but I did not extensive tests because I prefer to use ACR on productions for several practical reasons.
By the way, the Adobe answer about this one is that P65+ files, while ACR "sees" and opens them, are not officially supported (P45+ is, P65+ is not). I'm not in touch with PhaseOne support, but I'd like to have more data on this issue.
I'll be glad if some P65+ owners would gently do a quick test with their files - I'm not sure whether is an ACR issue or a digital back... feature
The steps could be the same: with a picture of a fairly neutral subject, ACR zeroing everything, convert to Lab, equalize the "a" channel (the "b" is, strangely, unaffected). Believe me, if the "a" channel shows the problem, you will recognize it.
Thanks in advance for your help,
Davide