Thursday, January 8, 2009

Editing A2Bn Transforms

Basically, after quite some time, several years, in fact, in the color management universe, I finally got around to editing my profiles.  I tried this a few years ago, and didn't get anywhere.  I just remember getting a preview that was completely broken (and appeared super-dark with only dark-red tints).  I gave up on that for a while, and just settled for the fact that the soft-proof was really only an interpretation, and learned to adjust my "seeing" to accommodate the differences between the soft-proof and print.

No more.

There are a few things that can be done:

  • Adjust print profile to make print lighter, to match the on-screen soft-proof.
  • Adjust print profile to make soft-proof much darker.
  • Adjust monitor profile for a much higher gamma value (e.g., greater than 2.2).

I ended up doing the second, but not before trying the first.  Here's what important to remember.  When the printer can print high density blacks, and when the CMM uses Black Point Compensation, (apparently, something both Adobe and Qimage can do), there's a damn good chance that the soft-proof will appear too bright.

First, I adjusted the reverse transform to make the print lighter.  This made some amount of sense.  But, I wasn't able to tweak the image that much in the transform.  And, I realized that I wasn't matching the print to the soft-proof; I was just matching the print to its appearance in LR2.  Which is stupid, since LR2 doesn't have soft-proof capabilities, and isn't really appropriate for final image correction anyway (which is kinda revolting, when you think about it).

While editing the B2An transform, I chose the perceptual intent.  That made sense, since I was printing with the perceptual intent anyway (though that's another issue I have yet to really explore).

Then, I learned that editing the forward transform, the A2Bn transform, I could change just the soft-proof appearance, without altering the printed output.  So, I cranked down the lightness curve in the forward transform.

FAIL.

It took a few minutes to understand what was happening.  It quickly dawned on me that while editing the A2Bn transform, I chose perceptual because I had done it for the B2An transform.  A moment's thought reveals the flaw.  The CMM take the image, and uses the embedded profile to go from embedded (e.g., ProPhoto RGB) to PCS (e.g., LAB).  Then, it uses the reverse transform to go from PCS to Printer space (i.e., the space described by the printer profiles I've been editing all this time).  This is how a print gets made.  It's why editing the Perceptual intent works when I'm printing, using the Perceptual intent.

But, why doesn't soft-proofing work when I'm editing the A2B0 (perceptual) profile/intent?  Simple.  A soft-proof is a colorimetric rendering of a device's color space.  So, on a soft-proof, we use forward from embedded to PCS, then reverse from PCS to device, then forward again from device to PCS, and finally, reverse again from PCS to monitor space.

It's the 3rd step that's the doozy; the reverse transform from PCS to device probably ALWAYS uses the colorimetric intent, because it is trying to simulate the color EXACTLY within the monitor's available gamut (even with white-point compensation, that's still the relative colorimetric intent).

Still an open question: does PS CS3 use the "Monitor Desaturation" when soft-proofing...?

So, when I was editing A2B0, I was doing something that made no sense from the soft-proof perspective; i.e., trying to render an accurate picture of the device space in monitor space perceptually, not colorimetrically.  Once I changed to editing the A2Bn profile using the colorimetric intent, my soft-proofs were changing accordingly.

Result?  Prints that not only match in hue, but also now in lightness.

:)))

Corollary?  LR2 (and raw workflows) are still cumbersome.  Why soft-proofing wasn't built into LR from conception is a flawed concept.  One can only hope that the image is being color-managed; i.e., the custom ProPhoto-like space (with a 2.2 gamma) is going into LAB and then back out to monitor space.  I suspect that's the case, since PS CS3 shows the image virtually the same (2 ACDs, with slightly different panels and profiles).

Still, this going out to PS CS3 to make the final color/lightness edits, and then going back to LR and *THEN* exporting to Qimage in Parallels is awful.  Why can't Adobe buy Qimage, and put their interpolation into LR2?  Why can't Apple allow MacOS X to let the application control printer color management if it wants to?  Why can't Epson make drivers that have a truly "expert" setting, which would essentially allow you to just telnet to a port, and stream data to it, where that data stream simply describes the image at the max allowed resolution, and the prints just prints at the (x,y) you want, at that resolution, with the pixel data you give it?

Finally, why can't LR2 allow destructive edits to happen by just creating yet another virtual copy, and applying the edit?  They could be flagged in a special way that simply managed the asset while indicating that the file is now out of raw space, and into raster space?  And, allow plug-ins to operate using this mechanism, the way Aperture does?  One can only hope customer pressure will eventually create a single solution for managing images that don't require extensive editing.

Well, what is 'extensive' you ask?  Where is that line?  Well, if I were to asked to make that decision, it's simple: design the API to enable edits that affect the entire image.  Meaning, whatever decision is being made, it must be made to the entire image.  Of course, once you allowed per-pixel editing, people could use the mechanism to implement things like layered edits, etc.  And, that would subvert the "purity" of the LR2 raw-only workflow.

My rebuttal?  "So the frak what?!?!?!?"

I want to never leave my asset management tool, because I want the editing functions to be built-in.  If that makes my tool lose some of its design purity, so be it.  I want a seamless workflow, from import to print.  Taking the CF card out of the camera and putting it into the reader on my desk is the last inconvenience I should have to deal with before making a print.

There--I've said it.  I hope it keeps Narayen up at night.

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