16 bit to 8 bit workflow

D
Posted By
DavidMadison
Nov 11, 2003
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410
Replies
5
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Closed
Prior to CS, I did my initial major color / exposure corrections in 16 bit, of course without using adjustment layers since these were not available in
7.01 16 bit files. Then I would dump the file down to 8 bit for further
work.

Yesterday while working on a file, I started in 16 bit, and used adjustment layers to apply some significant curve moves to an image that needed major help. Very nice to be able to use several layers, click on and off, etc…. Then without flattening or merging those adjustment layers into the background, I dumped the file down to 8 bit. The adjustment layers remained in place.

Then I had the sudden realization that while I had used the new adjustment layer feature of 16 bit CS files, by not flattening or merging those layers into the background, I really hadn’t accomplished the goal of making those adjustments in 16 bit data since I had not merged the layers before dropping to 8 bit.

Can someone verify that this is correct?

David Madison
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16-bit bit workflow

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SB
Scott_Byer
Nov 11, 2003
Correct. If you want to retain the 16 bit fidelity of the adjustment layers, you’ll have to flatten before going to 8 bit. If you don’t really have that much to do in 8 bit, you might consider staying in 16 bit longer into the process (since nearly everything is there now) to give yourself more flexibility (though there are performance considerations with this as well).

-Scott
D
DavidMadison
Nov 11, 2003
Thanks for the confirmation, Scott.

David
GM
Glenn_Mitchell
Nov 12, 2003
The differences will almost certainly be marginal.

I just took an image with lots of shadows and highlights, not a lot in the midtones. Applied a substantial RGB curve (63 to 126).

Version 1 — applied the curve directly to the image than converted to 8 bits.

Version 2 — use a curve adjustment layer, same curve, convert to 8 bits, flatten.

Version 3 — convert to 8 bits, apply same curve

Version 4 — apply same curve via layer, flatten, convert to 8 bits

Statistic 1 2 3 4
————————————————–
Mean 58.23 58.55 59.21 58.48
Std. Dev. 65.12 64.30 65.19 64.32
Median 36 36 37 36

Now, compare columns 2 and 4. There is very little difference whether you flatten and convert or convert and flatten. The slight differences in the numbers do not add up to any visible difference.

I agree that the advice to postpone converting to 8 bits as long as practical is generally good advice. But if the curve was your last adjustment, whether you flatten before or after the 8-bit conversion appears to have no practical consequence.

This was just a quick and dirty empirical test. Feel free to check this out against a bunch of images. 😉

Cheers,

Mitch
R
robertfeinman
Nov 12, 2003
For a visual example of the differences between 8 bit and 16 bit workflow, look at the latest tip on my web site.
Follow the tips link on the home page..

<http://robertdfeinman.com>
GM
Glenn_Mitchell
Nov 12, 2003
Robert, no one is disputing that performing nonlinear edits in 16-bits has important advantages over 8-bits. Of course it does, and that’s why many of us convert our RAW images exclusively to 16-bit TIFFs.

The question was whether one should flatten 16-bit layers first and then convert to 8-bits or whether it would significnatly degrade the image to convert to 8-bits first before flattening. In either case, the edits were all done in 16-bits using adjustment layers.

My point was that it appears (to my eye with the image and the numbers associated with the histograms) whether one flattens or converts to 8-bits first.

Cheers,

Mitch

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