U of S | Mailing List Archive | alt-photo-process-l | Re: OT: 16 bit editing myth or reality?

Re: OT: 16 bit editing myth or reality?

Happy holidays to you and all others on the list.
In my last message, I hope I was able to tell every one the context in which this (my) experiment was done. Though I think most of the list member had the intuitive or learned knowledge that working in higher bit resolution would minimise quantization errors or simply result in higher quality image, it wasn't obvious to me and probably to most of us here how this improved quality translated into actual quantitative values.
As for doing what you suggest below, it should be obvious that such an exegarated transform would result in poor quality image for both resulution, though the 8 bit would probably suffer the most. (I like very much porcupines...)
If I where to do an in depth analysis of the "benefit" of using 16 bit resolution on B&W image, I would try to recreate a typical set of editing transformation as would be done on an actual image. Any out of the ordinary editing would be counter productive in my opinion and the result wouldn't be that useful since they wouldn't have any connection to real world image and real world editing. In this type of analysis I would also use PS for the simple reason that recreating the math behind some of the editing transform would be way to much work and it wouldn't be relevant to the initial goal. When all four image would be ready to print that is image #1: original unedited 16 bit image, image #2: image #1 converted to 8 bit, image #3: edited from image #1 and image #4: edited using the same editing step as for image #3 but from image #2 instead, to be print ready image #3 would have to be converted to 8 bit. Then I would load image #2 to #4 (image #1 is redoundant) in my program or whatever to count the looses if any. I could also do a little bit better by recording each individual editing step by itself, this would allow one to evaluate the contribution of each type of editing transform and the more global result of applying all of these transform steps together. To be even more complete, this analysis could be done on a color image and the stats should also include CIE delta errors (1976) this would give a more complete picture then just measuring quantization errors as I did.
I'll first seach to see it as been done before and if not, I just might give it a try out of curiosity and provide you with the result.
----- Original Message -----
Sent: Sunday, December 16, 2007 1:24 PM
Subject: Re: OT: 16 bit editing myth or reality?


If you have a good 16 bit image, try this:

duplicate the image and convert to 8 bits.

Take both images and do a levels adustment by only moving the white point slider to the left until you hit a value of say 50.  This will compress the date a great deal.

Now do another levels adjustment and hit AUTO.... examine the histogram of both images.  You will see that the 16 bit image has no gaps in the histogram and there is still enough fidelity to make additional adjustments.

The 8 bit image is going to look like the back of a porcupine.

It has long been the standard to work in 16 bit.

I might add though that Photoshop is actually a 15 bit program.  If you work with Camera Raw or Scans where the software does do true 16 bit, best do as much of the adjustments that you can there.

Happy Holidays

Best Wishes,
Mark Nelson

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