"Bill Hilton" wrote in message
I’ll try to show an image that does illustrate the advantages of 16 vs 8 bit edits below but first …
[re Fraser’s use of gradients to illustrate the hibit advantage]
http://www.creativepro.com/story/feature/7627.html I showed that particular image because you were challenging Fraser’s use of gradients to make his point … the image I showed has natural gradients similar to what Bruce used, albeit over a much narrower color range. My point was that such gradients do occur in photos at times. Since my image was exposed properly it requires little editing, but because of the saturated reds it looks much better converted from the RAW into a wider gamut space like Ektaspace and then converted to a tighter gamut profile with perceptual rendering, so for that reason I would want to keep it in 16 bit mode. Had it been over or underexposed you would probably see what Fraser was showing with his example.
I’ll stick with my contention that Fraser’s article is flawed. In the interest of not repeating myself, let’s accept, for now, Fraser’s use of artificial images, as part of an experiment to illustrate, in an abstract way, the concept of 8 versus 16 bit manipulations.
Since one of the most basic requirements for an experiment is reproducability, I think it is reasonable to ask that we be able to recreate the result ourselves.
The Fraser article does not provide the original images, or any description, that I could find, on how to recreate those images. So I created an image that resembles the one Fraser used in his article, using a horizontal spectrum gradient combined with a vertical black/white gradient in luminosity mode.
Here’s the surprise: I applied the same levels manipulation described in the article. The result: there is no visible difference in the appearance of the 16 and 8 bit results.
This took me all of 10 minutes to do, and I invite anyone reading this article, to do so themselves. You will need a version of Photoshop that supports 16 bit gradients.
Anyway, here’s another image you might find of interest … I spent the first 18 days of Oct in New England hoping to photograph fall foliage but it was a terrible year, the first week had record heat (mid 80’s instead of 50’s where I was) which killed the colors, then we had record rains and flooding, which didn’t help the photography.
I got this shot of a loon in a heavy fog one morning, I wanted a dreamy effect with just a hint of a shape to catch a mood …
http://members.aol.com/bhilton665/A2921_start.jpg … this is unedited from the RAW, shot at + 1 2/3’s off meter reading, and is still a bit dark. You can see from the histogram that only about 10% of the tonal range is used, with the bulk of the data between 214 and 235 or so. The light was so low contrast that an f/2.8 lens would AF but a f/4 lens would not.
Again, an interesting image.
So for this thread I converted twice, once at 8 bit/channel and once at 16 bits, and then set the black point on the loon’s neck and the white point on a bit of foam floating near the bird, basically spreading 30 data points across 245 points (I had the white point set for 245).
Here is the 8 bit result …
http://members.aol.com/bhilton665/A2921_8bit_setblackwhite.j pg Here is the 16 bit result …
http://members.aol.com/bhilton665/A2921_16bit_setblackwhite. jpg
Both links point to what appears to be the 16 bit image. Earlier this afternoon both of them pointed to the same 8 bit image. While you are fixing this, I’d like to know if you did your editiing in a wide gamut space such as Ektspace?
Two concessions before you say anything … 1) yes, this is an extreme tonal change and 2) both look like crap at 100% … no argument from me on those points, but to me the 16 bit version looks less crappy with less noise. And from the histogram you’d infer that further edits (perish the thought) would cause less damage with the 16 bit version.
Re the histogram, I reject it utterly as a sole measure of image quality. If there are problems it should be visible in the image as well as in the histogram. Furthermore, Photoshop injects fine noise when converting from 16 bit to 8 bit, and this added noise will "fatten" the histogram, and make subtle transitions smoother.
Now while you (or at least I) wouldn’t make such a radical tonal shift with this image (I like it the way I shot it) I did get asked to darken the bird when I posted this image on a web site … here’s the image I posted, created from an 8 bit conversion btw … (click ‘back’ to see others from the trip that are not so foggy 🙂
http://members.aol.com/bhilton665/fc2005/loon_A2921_b.htm … the first person to view this told me they could hardly see the bird and I needed to adjust it, so if I were to do this I’d make a less drastic move of the black point than in the example, but still a fairly major movement. At some point you start to see the difference between making an edit like this in 8 bit vs making it in 16 bit. Exactly how far you have to move the black point before it becomes noticeable is something I’m not going to check, but at some point … if I’m lucky enough to sell some large prints of this image I’ll certainly do the prep work on a 16 bit version.
This is your rightful decision about your own technique. Given your obvious excellent results, I respect your decision, even though it appears, so far, not to be based on the appearance of the image, but on your own estimation of the underlying quality. I do not trivialize this. I believe it is the right of every artist and craftsman to make many such decisions in the course of their work.
But, if you are going to recommend that others use hibit images for their editing, I think you should justify it by showing an actual image where you believe it makes a difference. Perhaps the loon image does this – I haven’t seen it yet.
Another poster in this thread wrote that some people are willing to go to more trouble for small quality improvements and I’d plead guilty to that … if I could get a 5% improvement for a 100% increase in effort I’d call it a bargain. I know others don’t feel that way but I do.
One last image, this time without the before/after … my wife shot this hummingbird earlier this summer and the image was about 1.5 stops underexposed because she had been shooting in a different direction with minus exposure compensation set (needed + for this light) and because the fill flash didn’t re-cycle quickly enough for the flash to be fully powered (something about shooting at 8 frames/sec when the flash needs up to 1.5 sec to recharge) …
http://members.aol.com/bhilton665/rufous_U8507.jpg … the tonal range wasn’t as limited as the foggy loon shot but it was still compressed, so when someone wanted an 11×14" print from a cropped area it looked smoother (in the print) going back to a 16 bit file than it did using the 8 bit version I had originally converted on the laptop for the jpegs.
Again, a beautiful image, but without the ability to compare the 8 bit and 16 bit manipulations it does not advance the contention that 16 bit edits give superior results.
The common thread in both of these examples (one high key, the other underexposed) is that you have a limited tonal range that gets expanded with heavy edits. To me that’s when 16 bits is better than 8 bits.
This may be the case, but without comparison images, we are reverting to talk. You did provide comparison images, and for the life of me, I cannot tell the difference between your 8 bit and 16 bit versions. Once again, I would like to compliment you on the quality of your and your wife’s images. The hummingbird image in particular is incredible!
To each his own.
We end in agreement. I quote from my first post to this thread:
"… many people, including some excellent professional photographers, feel that even an imperceptible difference in quality may eventually be significant to their images – if not now, then perhaps in the future. As a tool provider, this is enough reason for me to fully support both 8 and 16 bit manipulations in Curvemeister."
I would add to this that the work of many of these individuals who choose to work in 16 bit, as is the case with yours, Bill, is of excellent quality. As the evidence stands, I feel justified in asserting that there is no advantage to editing in 16 bits versus 8 bits.
Once again, I’m speaking of color images in the color spaces commonly used in Photoshop. Monochrome images, linear gamma, and some of the more exotic color spaces, such as ProPhoto RGB, are a different issue.
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Mike Russell
www.curvemeister.com