You are the one who introduced these terms into the discussion with irrelevant references to "out of gamut colors". You are thinking of gamut as a two dimensional CIE diagram, but forget that there is a third dimension involving luminosity as explained here.
Oh, please. You're carrying coal to Newcastle here. I'm well aware of the three-dimensional character of color spaces. You're the one defending the notion of raising the black point in an image file to something other than 0,0,0 as something that should be done on a consistent basis, rather than as a strategy to deal with saturated colors in the shadows or as a kludge to deal with a poor-quality profile with shadow problems.
The reason I brought up saturated shadow colors is because it one of the few instances where raising the black point of an image above 0,0,0 makes some sense. Raising the black point of an image above 0,0,0 can take advantage if the fact that gamut increases as luminance rises above the printer's black point. If shadow blocking is happening because the shadows of an image contain some very dark saturated greens the printer can't print, (common when there is foliage in deep shadow) raising the black point a little may in certain instances bring those greens into the printer's gamut. You trade a little DR for the wider gamut you get a little higher up the luminance axis.
Another strategy that can be useful is making a luminance mask, using it to select the shadows, and doing some selective shadow desaturation. This is usually a better option, as it allows you to keep 100% of the DR the printer has to offer, while avoiding blocking from out-of-gamut shadows. If done properly, the visual impact of the desaturation is minimal, but setting up the transparency curve for the selection mask can be a bit tricky to get right.
Again, you are missing the point. We are not talking about out of gamut colors. The eye does not perceive color at the black point and the OP did not complain about color shifts.
I'm not missing any point. The OP is complaining about blocked shadows. One cause of blocked shadows is saturated, out-of-gamut colors in the shadows that turn detailed portions of the file into dark, solid blocks of mostly-black. The posted image has a lot of saturated colors in the shadows, so it's one factor that needs to be considered.
Really,? I am the one who said he got good results from Costco, whereas you originally suggested that the OP go to another lab. Then you suggested that his monitor was mis calibrated.
I was trying to suggest the most likely cause of the problem, and that changed when I was given additional information. In the maintenance and medical fields, when there are multiple possible causes for a given set of symptoms, you start with the most likely one first. Sometimes you have to work all the way down the list of possibilities before solving the problem, but examining the most common causes first usually sames time and effort in the long run.
IMHO, he needs to do some nonlinear editing to brighten the quarter tones and not change the black point. A good profile will match up the black points. If you do your homework, you can get excellent results from Costco. However, recent photo ink jet printers exceed the gamut of the Noritsu printers with Crystal Archive paper and this is another reason to do your own printing (in addition to size as you mention).
We're in agreement here. That was part of the reason I got the 7600.
I'll tell you what Jonathan. I can upload my RAW file of the image we've been looking at, and you can do the adjustments using my Costco's profile, and then upload the jpg. I'll down load it and print it and then send the actual print to you in mail. Then we can REALLY see if Costco is the problem, or something I'm doing.
Would you be willing to do that?
Yes. Post a link to the RAW, and I'll do a workup on it with the posted profile as a guide, and post an 8x12 JPEG with a description of what I did. It may take a week or two, as I just shot a wedding and processing the shots has been occupying my limited spare time.