In the Aardenburg color target I posted earlier in this thread there is a black stripe running along the bottom of the image. In that stripe are sets of numerical values 1, 2, 3, 4, 5 followed by letters, R, G, B, C, M, or Y. the values 1-5 are, you probably can guess, encoded in increasing lightness values going from L* = 1, 2, 3, 4, and 5, and each letter is L*=6. I consider these to be the deep shadows in a digital image that a great print shouldn't throw away. If an output profile made with M0 measurements can print those deep shadow values in a perceptibly smooth ramp away from the stripe's max black (RGB = 0,0,0), then, IMHO, there really is no deep shadow problem to be concerned with on account of measuring one's profiling target data with the M0 condition. My own rolled profiles are usually able to print those values cleanly, so again I see no need to resort to M3 measurements to solve a problem I usually don't have. The profile I did make with the M3 measurements actually overcorrected, and worse, there was a subtle but still disconcerting visual jump between 5-15 in the higher shadow values that was then leading to an oddly flatter tone response for some colors in the 15-30 L* range. There were other subtle tone and color reproduction issues as well which could be seen in other areas of the 12 hue planes in that target. Perhaps the folks at Chromix have their own custom profiling software that works better with the M3 data sets. I only have access to i1Profiler, PM5, and BasicColor software and the M3 data set isn't playing as nicely as I'd like to see with those profiling apps.
When I do run into trouble with the lowest shadow values plugging up it is generally due to over inking by the printer. With limited "media settings" to choose from on typical desktop photo printers and the fact that some manufacturers do a better job at linearizing the printer than others, sometimes the reproduction of those deep values is not quite as good as I'd like. The 1, 2, and 3 L* tones can plug up in some of the colors, even the gray ramp. That said, my Canon Pro-1000 has beautiful ink ramps. It's a joy to build profiles for that printer, and the deep shadow detail is all there. My Epson P600 slightly over inks in the photo gray channels on some media/media setting combinations such that a minus percentage value in the density slider found in the printer driver's advance setting menu will help alleviate. Unfortunately, that density slider is a global one affecting all the ink ramps, so system color gamut can be lost if one tries to take the slider far enough negative to fully open up the grey channel ramp. It ends up being a bit of a compromise for some matte media. Glossy/luster papers rarely have an issue with the deep shadow reproduction values. Perhaps M3 measurements might be a way to rescue an over inking situation, however, paying close attention to what media is being selected to build the profile is usually the place to start.
Lastly, as for soft proofs needing some tweaking because the M0 data isn't a perfect match to what we see in the print, a good portion of that mismatch actually has nothing to do with the M0 data. It has to do with the customary way display profiles remap monitor white and monitor black luminance values to L=100 and L=0 respectively, no matter what the actual luminance range of your monitor really is. To simulate a true zero to 100 L* range the monitor's luminance range has to be over 700:1 (I've forgotten the exact calculation, but it's over 700) Many new monitors claim to have those specs, but in reality a great many fall short. Also, unless you don't mind image editing in a cave, the ambient room lighting adds a little veiling flare to your perception of monitor blacks. The end result is that the posted L* shadow values will be lifted a little lighter in reality and that contributes to the perception that the softproof of a matte paper is just a little bit flatter than it should be. The display's baked in tone curve error is not a big error, but it does add to the lower image contrast problem for softproofing matte media especially. I studied this display profile scaling error extensively in the days of CRT monitors that typically had luminance ranges no better than 400:1. I found that by using a profile editor like the one in the Profilemaker 5 suite or Kodak Colorflow software (as Ernst noted earlier) I could correct any perceived M0 data deficiencies and compensate for the actual display errors quite nicely just by rescaling the tone curve in the inverse transform LUT of the profile such that matte media black values of typically 17 or 18 would then post to the softproof view as if they were L*min of approximately 4L darker, e.g. 13-14. Thats all it took to get a near perfect match, and nowadays with higher contrast displays, I don't go to the trouble of making this profile edit anymore. I've learned to live with the slightly lower contrast in the softproof. It actually works to my advantage because it forces me to pay very close attention to the image edits needed to lay the image down beautifully on the print.
kind regards,
Mark
http://www.aardenburg-imaging.com