[Technical] Canon XPS Driver - is it really printing 16 bit (48 bpp)?

[16bit]

I am still learning this printer, and trying to work out exactly how I can get the best out of it.
Matching prints to screen is becoming such an impossibility, not in part to the fact that we haven't had a single consistent day of weather and ambient light since two days or so after buying the printer! I guess this tells me I need a viewing booth.

Story
I tested a couple of different High Pass sharpness techniques on an old scanned image I am restoring. Each time letting the printer handle colours and using the XPS driver.
After finally settling on what settings should work, I printed the full image, rather than crops. Great.
However, there seems to be hint of magenta cast compared to the other two versions ("soft as putty" and "gritty as sand" we'll call them).
At fist I wondered if I goofed up and missed adding an adjustment layer or used the wrong rendering intent or something dumb, but nope, doesn't seem like it.

I thought I'd take a peek at the print history in the Canon "View Print History XPS" tool in Windows start menu.
My last 10 documents were shown, complete with ugly colours for when I disable printer colour management (using Photoshop ACE for those). I found the full sized print and the overly sharp crop I made and they looked the same colour, no magenta hue on the large print.

Info and Question
So I searched for just where Canon is storing this history that it can use to re-print if requested.
On Windows 7 x64 it is here, for other OS I don't know.

C:\ProgramData\CanonBJ\IJPrinter\CNMWindows\Canon iP7200 series XPS\History\%username%

In this folder are plenty of text documents listing some settings for each print, which do seem to be identical for the most part, and important zip files (without extensions) containing some xml data (.xml, .fpage, .fdoc and .rels extensions) as well as an archived folder with 500px high slices of the image printed in .png format.
When I checked these .png files out they are only 8 bit (24 bpp), not the 16 bit (48 bpp) that I sent. So if I was to re-print using the XPS history, it's quite clear that it cannot make up the extra bit depth. This is for images where the printer has handled the colours or Photoshop has taken control.

It does make me wonder if it even prints in 16 bit at all.


Either way, thank goodness I can recall at least some of my images, as I do want to print them out exactly the same on another paper type for like-for-like comparison.

 

[StewartR]

This is mostly way over my head, but maybe I can help a bit, or at least help fill in the gaps for some more knowledgeable people.

You say the images you're printing is a scan of an old image. So I'm curious as to how it was scanned (bit depth/, resolution etc), what format it was saved in? Also, what software are you using to do the printing and how is it configured? It seems to me there are several potential failure points before you get anywhere near the XPS driver, and it would be sensible to make sure we've eliminated them.

 

[16bit]

Sure,
Scanned using 48 bit in Photoshop (32bit/x86 OS to access Canon TWAIN driver), saved as 48 bit TIF. Verified these are 48 bit / 16 bit images.
Edited in Photoshop in 16 bit mode (48 bpp).
Sent to printer from Photoshop - no option to switch 8 / 16 bit data.

Funnily enough I think I found an answer to all this, by searching around.
Adobe Lightroom and Photoshop don't offer a "print in 16 bit mode" option to Windows users, not from the included Adobe print dialogue. In Mac land, there is this feature/option. For Windows users to access the higher bit depth printing, it takes a 3rd party print plugin, just like what Canon supplies with their PIXMA Pro line of printers. This would bypass Adobe's print dialogue and enable 16 bit printing.

So, for Windows users Adobe just doesn't support 16 bit printing. But that said, I have read so many times that it just doesn't matter, and that the dithering being done by Adobe's own print engine is rather good and makes any difference imperceptible for the most part. There might be the odd person in a large group of people that may be able to tell a difference between the two, if they know they are different prints, but couldn't say which was better. This would require those kind of crazy colour gradient images that could demonstrate the smooth gradient transitions that dithering could make less smooth and more noisy.
Bottom line - edit in 16 bit by all means, there is good reason. But for printing, it's gonna be dithered to 8 bit, just move on and be happy.

Now, the fun part is that when I have instructed Photoshop to take control over the colour management, the image preview looks ghastly! I recall seeing these sorts of wacky colours when I messed up with the old printer and double-colour managed the image. I wouldn't be surprised to find that the print history preview is being colour managed regardless of whatever data was sent. This would make the print history feature next to useless except for when letting the printer manage the colours, or for simply finding out what was printed. I have not re-printed from the history, so cannot be sure until I do.