I've been otherwise engaged after getting an Isis 2 XL learning its capabilities and limits but it's time to address this internet color management myth. The myth goes back to an article at "The Online Photographer" where, at the end of the comment section Dave Polaschek, and Adobe color guru, makes the following statement:
http://theonlinephotographer.typepad.com/the_online_photographer/2015/10/photoshop-vs-printer-managed-color-printing.htmlPrinter Manages Colors guarantees a conversion to sRGB IF you are printing with a color profile attached to your image data. This is how StretchDIBits (which is the bottleneck routine used on Windows operates) works. ICM2, when designed by Microsoft back in the 90s, chose to use sRGB as their interchange space, so any image data with an attached profile, and with ICM enabled fed into StretchDIBits will be converted to sRGB.
In the case of the Epson 9800, using Printer Manages Color with ICM the option exists to assign the input to a colorspace which can be any in your profile directory. This experiment shows that assigning the input profile to ProPhoto RGB precludes conversion to sRGB in Windows and the full range of ProPhoto RGB will be used together with the selected printer profile and Colorimetric Intent.
A test was run comparing 478 patches in ProPhoto RGB containing printable Lab colors in 10 unit separations. The printer profile used was a custom 4k patch made with I1Profiler. This profile was used for "Printer manages" as well as Photoshop manages." Additionally, the "Basic ICM" was selected for the "printer manages" and "ProPhoto RGB was selected as the input colorspace. The usual (none) settings were used for Photoshop Manages.
This is the result for Photoshop Manages Color:
Mean DeltaE2000: 0.54, Max DeltaE2000: 1.90
Mean DeltaE1976: 0.90, Max DeltaE1976: 3.17
Best 90%, Mean DeltaE2000: 0.47, Max DeltaE2000: 0.92
Best 90%, Mean DeltaE1976: 0.77, Max DeltaE1976: 1.65
This is the result for Printer Manages Color:
Mean DeltaE2000: 0.53, Max DeltaE2000: 2.11
Mean DeltaE1976: 0.90, Max DeltaE1976: 3.44
Best 90%, Mean DeltaE2000: 0.46, Max DeltaE2000: 0.88
Best 90%, Mean DeltaE1976: 0.78, Max DeltaE1976: 1.49
Provided here are the results of printing 478 patches in Lab distributed around 10 units from L*=10 to 90 and a* and b* ranging within a printable gamut that exceeds Adobe RGB in places. Each patch is on boundaries of units of + or -10 to make it easy to visually scan for color error since the reference colors are fixed. To enable any others wishing to verify this I have provided a tif file of an Isis scannable image in ProPhoto, high bit RGB format. I have also included a reference patch file that includes the ProPhoto RGB values for each of the Lab 10 unit delta patches. Additionally, I have included captures of the Epson 9800 printer settings for "Printer Manages Color" that show what ICM settings were used in the driver. An included Zip file contains these so anyone interested that has an Epson 9800, and likely other similar printers, can verify this for themselves.
Zip File:
Epson 9800 Printer Manages Colors Settings.jpg - Screen capture of Epson 9800 settings
Histograms.jpg - Histograms of dE2k error distributions
LAB10 478 Patches.tif - CGATS LAB file of patches
LAB10 in ProPhoto .txt - CGATS RGB file of patches, the end is padded with RGB 255,255,255 for default Isis formatting
LAB10 Photoshop Manages.txt - CGATS file from I1 Profiler patch measurement
LAB10 Printer Manages.txt - CGATS file from I1 Profiler patch measurement