[filmscanners] RE: 16 vs 8bit scans

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

> From: Ed Verkaik
>
> With the above in mind, for those out there using NikonScan, does it
> make any difference if you were to save as NEF vs TIF in 14bit (16bit)?
> NikonScan will open and manipulate either one, so I'm not sure why
> someone would save in NEF.

I don't know what advantages the NEF format provides, if any. But TIFF
certainly contains all the image data.

> If there's no difference, and you then wanted to use the J2k instead,
> how easy will it be to change these files in the future? If you were
> considering further curves work, etc. would it be better to keep your
> masters in TIFF?

As I explained in a different thread, if I examine an image of pure blue
sky, from either a digicam or a scanned slide, I can see up to five counts
of noise in the numbers as I move the cursor around a very small area.
(That's five counts on a 0-255 scale, since that's what Photoshop shows.) If
I save an image in JPEG with a quality setting of 12, it compresses by
something like 10:1. If I reload it, layer it over the original, and select
Difference, I can see lots of 1's, quite a few 2's, a few 3's and 4's. If I
do the same with JPEG2000, and compress by the same amount, I can see quite
a few 1's, and only an occasional 2.

The point of this is that the errors introduced by 10:1 compression are
insignificant compared to the noise already contained in the image, even in
something that looks like a solid textureless color like blue sky. And
JPEG2000 is somewhat better than JPEG.

If I needed to store a partially edited image, to finish at a later date,
I'd probably just use PSD, because these are temporary files of which I only
have a few at a time on my disk.

> When you say "edit" do you mean changes to that image, or selecting
> amongst images? What size file does your 8bit file become?

I mean changing the image. I get something in the ballpark of 10:1
compression from JPEG with a quality setting of 12. With JPEG2000, I can get
greater accuracy _and_ preserve 16 bits per channel (actually 12, since
that's all my digicam or scanner produces) with the same file size. So
reducing to 8bpc JPEG doesn't save space over 16bpc JPEG2000. But I
generally save my final image as 8bpc JPEG because it's readily visible in
any program, or usable by any other person.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com


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