Doug, grateful if you would decode/unpack this:
- which application are you talking about?
- What is this "null transform mechanism" you refer to (I thought it is just several choices one makes with colour spaces and rendering intents, but please define).
- What is the dE 0.13 all about? dE(76), dE(00) and dE between what and what?
Adobe Photoshop 2018, desktop.
Null transform technique is a way to bypass color management in Photoshop while retaining the ability to position profiling target sheets easily across roll paper or whatever media is being used.
The technique is quite simple. Assign any printer profile to an RGB image. It doesn't matter where the profile came from or even if for a different printer. Then print using "Photoshop Manages Color (disabling in the driver)" and select the exact same profile. This is critical. It must be the same profile. Then print. It makes no difference what intent is selected or if BPC is selected. These are not used when the image is in the same RGB space as the printer profile. However, when this is done you get a pop up box saying "it appears you are trying to print without color management. Please use ACPU then a cancel and "get it" button. Hit the cancel and print.
This appears to be something they put in common code, possibly to deal with some intrinsic color management conversions occurring in the OS's printer data path. This has impacted the IOS PS versions at times in normal printing so may be an issue there when trying to completely disable color management. However, Windows has always printed perfectly fine targets w/o color management, since dropping the option back in CS5 or so by using the "null transform" technique.
Adobe's ACPU is seriously crippled. About half the time if I print out a tiff target using it using the default settings the XRite I1isis2 can't read it because it shrinks the image. Expanding the target 3% seems to work but is a kluge. And positioning a target on odd sized paper is painful even when doable with ACPU.
However, I take warnings seriously and so anytime there is an update in Windows OS or Photoshop I run two test prints, one from Photoshop and one from I1Profiler (which currently works) then scan them with the I1isis. The two should match within the usual tolerance of scanning two prints made at the same time and printer.
Comparison is done using PatchTool. I use the default set of 957 patches for a standard US letter paper. When comparing patches printed in this manner the statistics of duplicate pages printed with I1Profiler should match those printed using the null transform if it does, in fact, bypass color management. The .13 dE was DeltaE2000, my preferred metric for tiny differences. The dE1976 was .19. These were the average of all 957 patches on both printed sheets.
Caveat: This has always worked on Windows, but IOS is a different animal. I have no idea what happens there but I understand ACPU doesn't have the same shrinkage issue in IOS.