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

[digitaldog]

It also applies to conversion from 16 bits to 8 bits when printing/

Does it? Even if it does, one can still test this by:
1. Convert in high bit to the output color space to avoid dither, print the image in the output color space using ACPU, an older version of Photoshop that allows this or another utility similar to ACPU.
2. Keep everything in 16-bit, turn off the 16-bit check box in the printer dialog box.
3. I'd submit that such testing at the very least should be done, on the Mac (for Epson) using a driver that specifically has this check box because newer drivers have no such option and despite my questions to Epson, I haven't received an answer if the newer drivers still pass all high bit to the driver or not. I kind of suspect not, here's why and yes, it's a massive assumption: the high bit check box wasn't available on Windows. This probably didn't make Windows user aware of this happy. It makes some sense to remove it on the Mac as they've done with my P800. That doesn't mean on either Mac or Windows, newer drivers don't 'detect' 16-bit and pass it along if found. But since no one here has provided much proof it makes a visual difference, it would make some sense to simply make it all disappear.
YEARS ago when I was working on the Epson Print Academy I asked the product manager in the US for pro printers why the check box was there if I couldn’t see any difference. He said that 'someday' in the future, the printers might be able to use this additional data and it could be seen on output. I don't believe that day's arrived yet.

[elliot_n]

It doesn't affect 16 bit to 16 bit conversions

So I don't understand why you said:

'Just turning on the dither option eliminates any advantage 16 bit driver paths provide.'

[Mark D Segal]

Does it? Even if it does, one can still test this by:
1. Convert in high bit to the output color space to avoid dither, print the image in the output color space using ACPU, an older version of Photoshop that allows this or another utility similar to ACPU.
2. Keep everything in 16-bit, turn off the 16-bit check box in the printer dialog box.
3. I'd submit that such testing at the very least should be done, on the Mac (for Epson) using a driver that specifically has this check box because newer drivers have no such option and despite my questions to Epson, I haven't received an answer if the newer drivers still pass all high bit to the driver or not. I kind of suspect not, here's why and yes, it's a massive assumption: the high bit check box wasn't available on Windows. This probably didn't make Windows user aware of this happy. It makes some sense to remove it on the Mac as they've done with my P800. That doesn't mean on either Mac or Windows, newer drivers don't 'detect' 16-bit and pass it along if found. But since no one here has provided much proof it makes a visual difference, it would make some sense to simply make it all disappear.
YEARS ago when I was working on the Epson Print Academy I asked the product manager in the US for pro printers why the check box was there if I couldn’t see any difference. He said that 'someday' in the future, the printers might be able to use this additional data and it could be seen on output. I don't believe that day's arrived yet.

Andrew, just so you'll know, for the Epson SC-P5000, released some time after the SC-P800, driver for OSX, the "Send 16-bit data" checkbox is alive and well - I see it here staring me in the face. We don't know in any detail what happens process-wise under the hood if one leaves it checked or unchecked, but it's there as an option to exercise. There is no guidance in the Manual about what to do with this option; however the link to an Epson support page I provided many posts back explains the principle behind it; now we all know there can be big disconnects between principles and perception, but at least it probably tells us why they think it's a good idea to provide it. Once it's there, I see no downside to just leaving it checked.

[digitaldog]

Andrew, just so you'll know, for the Epson SC-P5000, released some time after the SC-P800, driver for OSX, the "Send 16-bit data" checkbox is alive and well - I see it here staring me in the face.

So much for consistency in drivers. 
So does the P800 not do this or it does behind the scenes of Epson decided to bring it back?
Also, you're on a Mac right? Any idea if that option shows up on the Windows driver?

[faberryman]

Once it's there, I see no downside to just leaving it checked.

Also, there is no apparent upside to leaving it unchecked. Perhaps that's why it has been eliminated in some versions.

[elliot_n]

It also applies to conversion from 16 bits to 8 bits when printing

Yes, this was the only way I could get banding when printing my 16 bit grey gradient: deselect the 16 bit checkbox in the Epson driver, and also deselect the dither checkbox in Photoshop's colour settings.

[digitaldog]

Yes, this was the only way I could get banding when printing my 16 bit grey gradient: deselect the 16 bit checkbox in the Epson driver, and also deselect the dither checkbox in Photoshop's colour settings.

Yet dither should reduce banding.

[Mark D Segal]

Andrew, yes I'm on OSX 10.11.6 (El Capitan). I have no idea what the situation is with Windows - left that world in 2010. You know, just to show how unimportant this whole question is, you'd have a very hard time discerning a quality difference between a P800 print and a P5000 print unless your photo had a significant presence of colour that is outside the P800 gamut potential but inside that of the P5000 (because of the orange and green inks). That, based on observation when I was doing side-by-side evaluation.

[elliot_n]

Yet dither should reduce banding.

It did.

[digitaldog]

Andrew, yes I'm on OSX 10.11.6 (El Capitan). I have no idea what the situation is with Windows - left that world in 2010. You know, just to show how unimportant this whole question is, you'd have a very hard time discerning a quality difference between a P800 print and a P5000 print unless your photo had a significant presence of colour that is outside the P800 gamut potential but inside that of the P5000 (because of the orange and green inks). That, based on observation when I was doing side-by-side evaluation.

I think it's a useful question to see if indeed Epson is going back to 2010 by providing a driver that does or doesn't allow this option on both platforms, but I absolutely agree the entire discussion is moot because it doesn't matter.

[digitaldog]

It did.

Begging the question then, why did high bit data produce the banding you see? That shouldn’t be the case.
All this stuff about dither is only important IF we know it appears or not when measuring the output to see if high bit vs. 8-bit per color printing produces a visible or measurable difference alone. Dither adds another component into the mix, making it much harder to do an Apples to Apples analysis. IF indeed Dither is being used for a print.
With high bit data, we should never see banding anywhere (in the image, on a print, on a display). With 8-bit per color, that's a possibility. So we're hearing, if I understand you correctly, that with presumably dither added to 8-bit per color output, no banding but with 16-bit printing we do? That doesn't sound right to me..... 

[elliot_n]

Begging the question then, why did high bit data produce the banding you see? That shouldn’t be the case.

Hmm, something is getting lost in translation

Here's the test I did (pasted from the post I made earlier):

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I've been doing some further tests, printing some gradients (white to mid grey) with my normal print workflow (i.e. with a print profile (in this case, the Epson 3880's canned profile for Semigloss), 2880 dpi, high speed off).

I made 4 prints, all of the same 16 bit file (i.e. I'm not converting the file in Photoshop to 8 bit for the 8 bit tests - I'm just unchecking the 16 bit checkboxes in the Epson dialogs.)

1) Epson 16 bit. Photoshop Colour Setting = no dither
2) Epson 16 bit. Photoshop Colour Setting = dither
3) Epson 8 bit. Photoshop Colour Setting = no dither
4) Epson 8 bit. Photoshop Colour Setting = dither

They all look the same, with smooth gradients, except for (3) which shows some slight banding.

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[digitaldog]

Hmm, something is getting lost in translation

Here's the test I did (pasted from the post I made earlier):

----

I've been doing some further tests, printing some gradients (white to mid grey) with my normal print workflow (i.e. with a print profile (in this case, the Epson 3880's canned profile for Semigloss), 2880 dpi, high speed off).

I made 4 prints, all of the same 16 bit file (i.e. I'm not converting the file in Photoshop to 8 bit for the 8 bit tests - I'm just unchecking the 16 bit checkboxes in the Epson dialogs.)

1) Epson 16 bit. Photoshop Colour Setting = no dither
2) Epson 16 bit. Photoshop Colour Setting = dither
3) Epson 8 bit. Photoshop Colour Setting = no dither
4) Epson 8 bit. Photoshop Colour Setting = dither

They all look the same, with smooth gradients, except for (3) which shows some slight banding.

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But we're being told Dither is taking place at the print path IF I understand correctly, so I don't see how you've altered #3 differently than #4. Now for the color space conversions from working space to output space, that WOULD apply. Which again is why I'm suggesting the only 'fair' test here is to convert to the output color space in high bit, then pass the data to the driver when it's converted in such a fashion OR it's not a fair apples to apples test to determine what the driver, not Photoshop (which isn't the only product that we can print from or has such dither features) is doing.

[Mark D Segal]

I have always been under the impression, based on stuff I've read previously, that dithering takes place in the printer driver as part of the recipe for laying down the ink. Or is this about some other kind of dithering? This thread on our Forum may help: Doug Grey on Dithering

[faberryman]

Once it's there, I see no downside to just leaving it checked.

Also, there is no apparent upside to leaving it unchecked. Perhaps that's why it has been eliminated in some versions.

[elliot_n]

I'm somewhat out of my depth here

I performed these tests as Doug Gray suggested that by having dither selected, I was throwing a spanner into the 16 bit printing pipeline.

I couldn't see any evidence of that.

I did see that having dither UNSELECTED, caused banding when sending a 16 bit file into an 8 bit printing pipeline.

(FWIW, I'm using 'Photoshop Manages Colors' in the Epson print driver, Relative Colorimetric, and BPC.)

[elliot_n]

I have always been under the impression, based on stuff I've read previously, that dithering takes place in the printer driver as part of the recipe for laying down the ink. Or is this about some other kind of dithering?

Yes, this is about another kind of dithering.

[Mark D Segal]

Yes, this is about another kind of dithering.

OK, what kind of dithering is this and where do I find it?

[elliot_n]

it's dithering of the image file to prevent banding.

[Mark D Segal]

OK, what kind of dithering is this and where do I find it?

Yes, I know what it's for - that's one reason amongst others depending on the printer; but I'm asking WHERE you control whether it is active or not.