Thank you so much Robin for taking the time to explain this new SNI concept. Is this something that can simply be evaluated using an i1Pro? With Spectrashop? I’ll head to your web site next to pursue the links you kindly provided. I would not have suspected that the N9.5 patch on the ColorChecker chart to be less “spectrally neutral” than the N8 or N5 patches. I have the Munsell Grays swatch books in both Matte and Glossy finish, it will be interesting to see what kind of SNI these are. I also have some “gray” NCS swatches… I guess it would also work on my calibrated BCRA tiles? Best / Roger From: Robin Myers <robin@rmimaging.com> Sent: Saturday, June 22, 2019 1:31 PM To: Roger Breton <graxx@videotron.ca> Cc: 'colorsync-users?lists.apple.com' List <colorsync-users@lists.apple.com> Subject: Re: Exposure Value Hello Mr. Breton, When you are looking for a new gray card, may I suggest that the SNI value calculated in SpectraShop may be of use. The SNI is the Spectral Neutrality Index, a value which I have developed to evaluate neutral references. This value is an indicator of a specimen's spectral uniformity. The scale is 0-100, with 100 being a spectrum that is monotonic in value. Here are some example SNI values. Perfect reflecting diffuser 100 Fluorilon FWS-99 2009 99.9 Spectralon SCS-99 99.7 Kodak Gray Card 1977 (3 specimen average) 95.0 ColorChecker Passport 2013-12 Neutral 9.5 52.2 ColorChecker Passport 2013-12 Neutral 5.0 95.2 The SNI formula is based solely on the spectral values, no perception is involved. This allows for material evaluation alone. Notice that the white patch (Neutral 9.5) of the CC Passport has a much lower SNI than the Neutral 5 patch from the same chart. This is due to the high absorbance of violet wavelengths by the titanium dioxide colorant used for the white and also the slightly yellow color of the same titanium dioxide. This can be readily observed by placing a Fluorilon or Spectralon 99% reflecting tile (scintered PTFE) next to any white material containing titanium dioxide (TiO2). The TiO2 material will appear slightly yellow since the human vision system will adapt to the tile’s white, allowing the true color of the TiO2 to be observed. The SNI value was created specifically to answer questions about which material is more spectrally neutral. I find it very useful for checking gray reference materials such as gray cards. These articles on my website may also be of use. Neutral References for Digital Camera Calibration http://chromaxion.com/information/neutral_references.html Gray or White Card for Neutral Balancing? http://chromaxion.com/information/gray_or_white.html Regards, Robin Myers Robin Myers Imaging robin@rmimaging.com <mailto:robin@rmimaging.com> robin@chromaxion.com <mailto:robin@chromaxion.com> 925-519-4122 On 21 Jun 2019, at 19:14, Roger Breton via colorsync-users <colorsync-users@lists.apple.com <mailto:colorsync-users@lists.apple.com> > wrote: Dear Ilah, Thank you so much for applying your vast technical expertise to my humble problem. I realize, again, that there is so much to learn in digital photography, I feel ashamed to have neglected digging into this fascinating part of image processing for so long (It took me more than a few CPU cycles of my brain to figure Exposure Value, today)... For sure, I need to invest in a "new" gray card, I confess that this one has seen its share of "tales from the trenches". Having said that, I'm relieved to read in your analysis that my camera "light meter" isn't playing tricks on me or need to go back to the manufacturer under warranty. I *will* reshoot, for sure, as you suggested. It's an exercise worth every effort and probably investigate using one of your suggested software.. For now, I am not sure what to conclude from my experience? Tomorrow, I will probably experiment with shooting A) RAW alone and shooting B) RAW + JPEG. In "theory", there should not be any difference between the two modes of shooting but if there should be one, then this is going to prove interesting. Have you had a chance to take a look at my Excel sheet at all? To see whether I correctly applied the metering equations from measured Luminance and Illuminance? I think the calculations are sound. One last thing I have not tried and I *will* try is, to shoot with my antique D100, in RAW, to compare with shooting the same scene with the D810, in RAW, to test any potential differences between the two systems, in terms of exposure. One thing I wonder, as I was thinking about the experimental setup, something completely absurd (?), was, what that, could there be any difference in the underlying capture of the pixels between the two cameras? Suppose, on the D810, at 1/200s, F/5.6, ISO400, the histogram looks skewed to the left, suggesting some degree of under-exposure (see my earlier links)? Suppose further, on the D100, at the same 1/200s, F/5.6, ISO400 settings, the histogram looks "normal", with pixels distributed throughout the tonal range, from 0 to 255, then what? Until I'm convinced that there is nothing wrong with this camera, I figure I need to further test it, until I'm fully satisfied that there is nothing "wrong" with it. Best regards / Roger -----Original Message—— <snipped for brevity>