Discussion of 16 bit image editing vs 8 bit

Since the new version of photoshop adds improved 16 bit image processing I
decided to see if there is much difference between editing 16 bit and 8 bit images.
So I've added a tip highlighting the differences between using 8 and 16 bit
depth files for capture and editing to my tips page.
I did the same edits on both versions of the image using photoshop 7.

I leave it to you to decide as to the results, I'm still pondering the
meaning..


Follow the link to the tips section on my home page and then scroll down
to the New! tips.

 

Good page.

One thing to keep in mind is that PS adds 1/2 bit of noise when it converts
from 16 bit to 8 bit. I've seen discussions of 8 vs 16 bit that ignore this
and rely only on histograms to illustrate the "point" that 16 bit is
superior - yours is a refreshing change from this because you actually
compare the two images..

Much of the difference between the two images, including the histogram
combing, may be due to that factor alone.

--

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

 

Well......The 16 bit, at that enlargement is what I would call a "tad"
sharper. Not a very technical term, I know. The question would be,
would the difference be perceived in a normal print by the average
viewer? Probably not. At an extreme enlargement, pixalization becomes
the overiding factor, I think.
My ideal print is one that is "perceived" to be as sharp an image as one
could get. Going back to my photo printing days, I remember the endless
lens testing, shooting and printing resolution charts to achieve the
sharpest possible image only to be defeated by the grain of the film.
Then there was the diffuse light sources vs. condensors.
To add to that, if you are old enough, there was the old debate over
Panatomic X vs. Plus X, and Microdol develpor vs. D 76 and a myriad of
other sharpness issues! The quest for sharpness never ends, but that's
what make this field interesting and challenging.
Robert

 

I'm unclear here. At what point did Photoshop "convert" this image? I
thought the page indicated that they were two discrete scans.

 

A grainy, film-based image is not the place you are likely to see any
difference between 8 and 16 bit editing. Posterization is more likely
to show up in a digital photo of a very smooth subject with a shallow
gradient that you want to change to a steep gradient, such as a light
blue sky that is burned in for dramatic effect. Also, stacking up lots
of adjustment layers and using Lab mode make posterization worse.

Although I routinely use 16-bit mode for any major adjustments, I
doubt that anybody is likely to see any difference between 8 and 16
bit editing for ordinary photographs that are reasonably well
exposed. But I do some weird things where it makes a big difference.

 

Flycaster wrote:

[re Photshop's treatment of 16 bit vs 8 bit images, c.f.
http://robertdfeinman.com ]

There are two different scans in Robert's example.

Photoshop converts from 16 to 8 bit when it displays the image, and when
calculating the histogram.

In both cases, the 1/2 bit of noise involved in that 16->8 bit conversion
can cause a change in appearance that would smooth out posterization and
banding, and also smooth out the histogram. This is just one of the issues
that make comparison of actual 16 vs 8 bit images problematical.

--

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

 

Huh, I did not know this about the histogram; I'd always thought it was
based on the actual underlying pixel data unless it was cached. It's odd
that Fraser/Blatner have never mentioned this quirk before, and it would
indeed make a true comparison problematic, or at the least somewhat
inaccurate.

 

And sharpness is not the whole issue either. I still use, and will
gone on doing so until they either stop making it or death overtakes
me (whichever comes first <g>) Kodak's Tri-X as my standard B&W film.
Why? Because I love the grain - i positively *want* to see the grain
;-)

 

To which I will add, that I agree. Were it not for my advanced age which
limits the time I can stand in a darkroom, I would still be doing the
same. I first and only preference was for Tri-X developed 1:1 in D76.
Nothing better!
Robert

 

I'm glad there's still a few of us left