How to test if a print was made at 16 bit?

[Doug Gray]

I'm not so sure.

This is their example (Doug's example?):

https://www.dpreview.com/forums/post/61793580

It is not clear how it was printed.

I can only induce banding like that if I print a 16 bit gradient with either:

1. Adobe Color Print Utility, with 16 bit unchecked

or:

2. Photoshop, with 16 bit unchecked, AND 'Use Dither' unchecked (in Photoshop's Color Settings)

Neither of these printing methods represent a set-up that would be used to make a normal 8-bit print. In a real-world scenario Photoshop would be used, '16 bit' would be unchecked, and 'Use Dither' would be checked. The resulting 8 bit print would be indistinguishable from a 16 bit print.

Adobe Print Utility only works with 8 bit images. I'm just guessing but there is a simplified TIF reading C utility shown in libtiff. It can read virtually any tiff format file but has the downside that it converts anything not in 8 bit to 8 bit.

I recommend Bills Black Ball that I posted earlier to verify 16 bit paths. It's in ProPhoto and doesn't need to be printed w/o color management to show banding from an 8 bit printer path where dither wasn't selected. Can be printed from LR too using RelCol w BPC. I have no idea if LR automatically dithers when printing to an 8 bit driver from a 16 bit gradient like Bills Black Ball. Perhaps someone will test it.

Printing from a 16 bit file w/o color management and w/o converting to 8 bits is done by most using older Photoshops that allowed it. They removed it years ago because of compatibility issues with Macs.

[digitaldog]

Adobe Print Utility only works with 8 bit images.

My copy prints 16-bit images, no problem. What makes you say this and why would Adobe not allow 16-bit images to be printed?
Just output my Gamut Test File in high bit to the 3880 using ACPU.

[elliot_n]

My copy prints 16-bit images, no problem. What makes you say this and why would Adobe not allow 16-bit images to be printed?

Yeah, mine too

Just output my Gamut Test File in high bit to the 3880 using ACPU.

So did I I was interested to see if there is any difference between selecting 8 bit or 16 bit, but I can't really see it (I do see it with Doug's Ball image).

[faberryman]

In a real-world scenario Photoshop would be used, '16 bit' would be unchecked, and 'Use Dither' would be checked. The resulting 8 bit print would be indistinguishable from a 16 bit print.

Why, in a real world scenario, would 16-bit be unchecked?

[elliot_n]

Why, in a real world scenario, would 16-bit be unchecked?

I imagine it would only be unchecked in a situation where a photographer was trying to establish whether there's a difference between printing in 8 bit and 16 bit.

[elliot_n]

I don't understand how apps relate to the Epson print driver.

Is the print dialog in ACPU a barebones version of the Epson print driver?

If it is, then when we use it to print Doug's ball target (or a slither of it, to save ink), at 8 bit and at 16 bit, we thereby demonstrate (to the OP) that there is a visible difference in Epson's 8 bit and 16 bit printing pipeline.

We can't do this with Photoshop*, because when printing from Photoshop, the Epson driver utilises Photoshop's dithering algorithm, which makes an 8 bit print of a 16 bit file looks identical to a 16 bit print. (*Unless we switch off dithering in Color Settings.)

Right?

(All my test prints from Photoshop have been done using 'Photoshop Manages Colors'. Whether 'Printer Manages Colors' handles 16 bit gradients in the same way is another can of worms.)

[digitaldog]

I imagine it would only be unchecked in a situation where a photographer was trying to establish whether there's a difference between printing in 8 bit and 16 bit.

Or for the marketing department to show it as a "feature' that most of us have found, doesn't do anything. 
If I had a dollar for every marketing dept at a display company telling us their displays produce billions of colors.... It's rubbish. But people see the 'spec's for a 10 bit display, then a 12 bit one and think the higher value is a spec that's important in buying said display.

[digitaldog]

Is the print dialog in ACPU a barebones version of the Epson print driver?

Not at all. More like a barebones copy of Photoshop that does one thing: Print an image. Using a print driver.

[Mark D Segal]

Until you begin to edit the scans after scanning them (if you do). Again, the added precision is about editing the data, if the data is edited.

That's correct. Depending on the quality of the profiling, the media, the scanner and the initial rendition from the scan software, scans can require some substantial pixel-bending and the 48 bit files are definitely more robust.

[digitaldog]

That's correct. Depending on the quality of the profiling, the media, the scanner and the initial rendition from the scan software, scans can require some substantial pixel-bending and the 48 bit files are definitely more robust.

Certainly when one needs a selective edit rather than a global one that should be doable in the scanner software.

[Mark D Segal]

Not at all. More like a barebones copy of Photoshop that does one thing: Print an image. Using a print driver.

Andrew, did we ever receive a definitive explanation of how ACPU really works? It definitely reaches into the printer driver, but once there, offers only a limited menu of options that the user can adjust (such as in the Printer Settings tab and the Advanced Media Control tab in OSX), on purpose, because the whole idea is to use it for printing a file that is both unedited and without colour management, the question being exactly how it gets around colour management in OSX. Some opinion suggests it uses the null transform method that Eric Chan developed before Adobe offered ACPU. Do you know the underlying principles of its structure?

[digitaldog]

Andrew, did we ever receive a definitive explanation of how ACPU really works?

I have absolutely no idea. For that or any other software product. So few of us need it anyway and it hasn't been updated for so long, I'm surprised it still runs (but it does).

[elliot_n]

Not at all. More like a barebones copy of Photoshop that does one thing: Print an image. Using a print driver.

But whose driver? Adobe's? Apple's?

It has a 16 bit option, but I'm assuming that when it is unchecked, it doesn't apply dithering (to the 16 bit file). Hence the banding.

[Mark D Segal]

Certainly when one needs a selective edit rather than a global one that should be doable in the scanner software.

Sure. Well, in SilverFast 8 Ai Studio one can do a considerable range of high quality global and selective editing, and under the hood SilverFast automatically always processes the file in 48 bit to preserve quality, but will then output the file to a 24-bit format if one so chooses.

[Mark D Segal]

Agreed about the editing which should always be done in 16 bits if possible. One can introduce significant artifacts editing in 8 bits. Especially if one has a heavy hand. It would be interesting technically to try editing both an 8 bit scan and a 16 bit scan but initially converting the 8 bit to 16. Not sure any visible difference would show up. But it's also a pointless exercise since just scanning to 16 bits/ch is simpler.

As I just mentioned, with SilverFast edits are always automatically processed in 16-bit per channel and this is under the hood - no user control; but the user can select an 8-bit output format if desired. It saves storage space, but there is no other advantage to it.

[digitaldog]

But whose driver? Adobe's? Apple's?

I don't understand the question. It is Adobe's baby no question. It uses any number of print drivers AFAIK. Why would there be any limitation for it to pass data (not color managed) to any driver? I can do the same with the ColorSync utility and a few other pieces of software not from Adobe.
Adobe didn't want to allow non color managed data to sent through it to a driver but we need that for printing targets (send the numbers as is to the driver). So around what was it, CS5, they didn't allows this rare print process. Because some complained or just to be good guys, the provided this utility. Something a color management software product should handle anyway to print a target. To allow this limited need, they provided the free ACPU. But it's not the only software that can do this.

[elliot_n]

I don't understand the question.

i'm asking whose 16 bit checkbox is that? Is it Adobe's? Or Epson's? Does it appear with whatever printer you have hooked up?

[Mark D Segal]

I have absolutely no idea. For that or any other software product. So few of us need it anyway and it hasn't been updated for so long, I'm surprised it still runs (but it does).

For Epson printers ACPU is the only thing I use for printing the targets, albeit aged but thank goodness still workable. It produces really correct results to judge from the multiple profiles I have generated from those targets, providing impressive accuracy of colour rendition and tone ramp on paper. If it stops working, one could of course also print the targets from i1Profiler. For the new generation of Canon large format Pro printers neither does well for profiling - it is better to use Canon's Print Studio Pro.

[digitaldog]

i'm asking whose 16 bit checkbox is that? Is it Adobe's? Or Epson's? Does it appear with whatever printer you have hooked up?

Sorry, which check box? Can you post a screen capture?

[Mark D Segal]

i'm asking whose 16 bit checkbox is that? Is it Adobe's? Or Epson's? Does it appear with whatever printer you have hooked up?

It's Epson's - at least with the SC-P5000 printer. I don't know for other printers but I would assume likewise as long as the printer supports it.