auto raw file type in vuescan - problem?

[tipicanu]

I may not be understanding correctly the way that this is
supposed to behave, but maybe there is a problem with
the "auto" selection under the raw file type in the output
tab in Vuescan (7.6.76).

I use a Minolta SDIII but I'm not sure it matters. The problem
is that when I scan B&W negatives to RAW, the raw files are
saved as 48bit rather than 16bit under these settings (and I ended
up with 26 54mb files after a batch session instead of 18mb files).

Input tab:
Scan quality: Archive
Media type: B/W negative
Bits per pixel: 16 grey

Output tab:
Save raw file: checked
Raw file type: Auto

About "Raw file type: Auto" the manual states...
"It should normally be set to Auto, which defaults to bits per
pixel of the scanner"

Does this mean the maximum bits per pixel that the scanner
is capable of, or what is specified for the scan in the input
tab? It seems like it should be the latter but does the former.
Why on earth would AUTO select a 48bit format to save
16bit input?

Am I missing something?

Thanks,
-Jeff

 

[Bart van der Wolf]

SNIP

I use a Minolta SDIII but I'm not sure it matters. The problem
is that when I scan B&W negatives to RAW, the raw files are
saved as 48bit rather than 16bit under these settings (and I ended
up with 26 54mb files after a batch session instead of 18mb files). SNIP
Why on earth would AUTO select a 48bit format to save
16bit input?

I didn't try it before myself, but the best guess I can make is:
It depends on the scanner...
Some scanners can be instructed to send Grayscale data trough the cable,
others send RGB. If RGB is returned, you have the option to select or
combine the least noisy channel(s). In that case Raw may be 48-bits instead
of 16.

Bart

 

[Mendel Leisk]

Why on earth would AUTO select a 48bit format to save
16bit input?

I am scanning Tri-X and outputting Vuescan raw files. I would advise
you to output 48 bit rgb format raw files, even though the source is
black and white film. In Input tab, set your bits 48 bit rgb as well.
The Auto setting outputs 48 bit rgb, as you noted. To save a little
space, enable tiff compression when outputting the raw file.

If you want to see the difference, try outputting 16 bit greyscale
raws (or convert in photoshop). Then do scan-from-disk, one from rgb
raw, one from greyscale raw, and compare. Finished files produced from
greyscale raw files have markedly poorer quality.

 

[tipicanu]

Hi Mendel.
Thanks for your reply.
I tried this and, as I suspected, the images are very nearly identical -
the brightness histograms are the same except for a negligible increase
in smoothness across the top of the histogram curve of the 48bit file.
To the eye, I can only notice (if I look really hard) the slightest bit
more contrast in the image from the 48 bit raw. I'd have to say that
there is basically no difference. I remain unconvinced that 48 bit scans
of b/w negatives are the way to go. Can you explain what the advantage
would be to having 3 samples (rgb) vs. only one when you're going to
convert back to 16 or 8 bit eventually anyway?

-JR

 

[Mendel Leisk]

Hi Mendel.
Thanks for your reply.
I tried this and, as I suspected, the images are very nearly identical -
the brightness histograms are the same except for a negligible increase
in smoothness across the top of the histogram curve of the 48bit file.
To the eye, I can only notice (if I look really hard) the slightest bit
more contrast in the image from the 48 bit raw. I'd have to say that
there is basically no difference. I remain unconvinced that 48 bit scans
of b/w negatives are the way to go. Can you explain what the advantage
would be to having 3 samples (rgb) vs. only one when you're going to
convert back to 16 or 8 bit eventually anyway?

-JR

Not in my case. I just tried again, converted a 48 bit rgb raw to 16
bit greyscale, and the output from this source file was very washed
out, by comparison. Looks like the dark end of the histogram just
dropped out, very flat, no contest. YMMV.

I would love to not be seeing difference. With my Scan Dual II (res.
per yours), my raws are between 35 and 50 megs with lzw compression.