You folks have stimulated some thoughts I've had recently.
There is an old saying, "When all you have is a hammer, everything looks like a nail."
For printers, we benefit from high accuracy spectrophotometers which provide repeatable measurements well beyond our ability to distinguish one color from the next. But while we can characterize printers in various ways using spectros there is a very important aspect of printing that escapes the printer profiling process.
Smoothness. With limited numbers of patches it is very difficult, impossible really, to determine just how smooth printed color transitions will be. Patches are a single color. There are 16 million, 8 bit RGB values in a printer's device space and a spectral scan of a 4000 patch set is only going to measure .025% of them. So determining how well a printer transitions from one color to another is too much a question of luck. Does it show up in the limited patch set?
A scanner, OTOH, has the ability to scan continuously changing colors. This makes detecting things like an abrupt 2 dE color shift more likely. What scanners can't do, is measure spectral info or accurately specific colors. However, they can, very precisely, measure small changes and that happens to be what human vision is most sensitive to.
It may well be that, when testing printers, finding a way to measure smoothness over hundreds of thousands of colors on a single letter size sheet may provide a better quality metric than just extrapolating from the limited data set that profile targets provide.
Anyone run across this use of scanners? Would it be possible, using scanners to identify the more non-linear printer areas, to allow creation of much smaller printer targets while perhaps even improving profile accuracy by including only patch colors where needed?