I was revisiting my process for making charts where the goal is to print with specific reflectivity. This involves printing all 256, 8 bit grays, then measuring and doing an inverse lookup to determine what 8 bit value is needed to produce a specific reflectivity. I use M2 (uv Cut) for that purpose and it worked quite well.
So, when I upgraded from an I1Pro uV cut to an I1 Pro 2, I assumed I could continue to use the same techniques. It turns out there are a few issues.
The I1Pro uV cut operates by a uV filter on the incandescent lamp. The I1 Pro 2 has a different approach. It injects a bit of uV but only narrowly over about 15 degrees. Whereas the incandescent lamp illuminates over an annular circle.
The I1Pro 2 makes an estimate of M2 and M1 by subtracting the spectrum on a second pass illuminated by the uV led. It adds a smaller fraction to create the estimate of the M1.
It actually works quite well. Normally. On glossy and semi-gloss papers. With or without OBs the results are reasonable.
But I've noticed a rather odd phenomena on matte. Specifically Epson Enhanced Matte which has a lot of OBs. When measuring a 256 patch set of gray tones there is, about 5% of the time, excessive injected response from the uV led pass in the darker patches This creates positive b* spikes that are often above 3 and sometimes over 6. Spikes on the M1 side are in the opposite direction and about half the magnitude. These are not correlated. Repeated measurements over exactly the same row without changing moving anything other than making additional row passes produces spikes in other locations.
Examining the spectrum, the spikes are produced during the led uV light pass and likely by tiny pieces of paper fibre containing OBs dragged by the instrument into the darker patches where they may be fluorescing. It's a small effect with a reflectivity difference around .01 between 420 and 470nm. As the patch reflectivity increases the impact of these diminishes. But at lower L values (L around 25-35) it's a significant effect.
I am curious whether this is seen with an Isis 2 and I will be testing that shortly.
It does not occur with spot measurements nor with glossy paper.
At this point I will not use M1 or M2 mode on matte papers to make profiles w/o making at least 2 chart scans and removing b* errors which is somewhat tedious. Averaging is better than nothing but an average of a *b error of 6 and no error is still an error of 3 and significant in rendering shadow detail correctly.
