Archiving: TIFF or PSP, 16 bit or 8 bit?

[Robert A]

Two questions, same subject:

How do you permanently archive your Vuescan files? Do you leave them in the
native TIFF format, or convert them to PSP? Moreover, do you leave them in
the original 16-bit, or convert them to 8-bit to save space?

-Robert Ades

 

[Mike Russell]

Two questions, same subject:

How do you permanently archive your Vuescan files? Do you leave them
in the native TIFF format, or convert them to PSP? Moreover, do you
leave them in the original 16-bit, or convert them to 8-bit to save
space?

Robert,

CD's and hard drive space are cheap. Archive your original raw scans, and
save your corrected images as well on the same disk. The amount of work
required to do each scan is much more important than the amount of storage
required.

If you have so many scanned images that the number of CD's is oppressive,
either switch to DvD, or consider saving as 8 bit tiff.

 

[Robert A]

Mike, my 4000-dpi 16-bit scans take up more than 100Mb each. Normally when
working in Photoshop, I convert to 8-bit right away. The reason I scan in
16-bit is for greater dynamic range and shadow detail. Once the scan is
done, is there any useful reason to keep that 16-bit data?

-Robert

 

[Mike Russell]

Mike, my 4000-dpi 16-bit scans take up more than 100Mb each.
Normally when working in Photoshop, I convert to 8-bit right away.
The reason I scan in 16-bit is for greater dynamic range and shadow
detail. Once the scan is done, is there any useful reason to keep
that 16-bit data?

Are you scanning medium format? I wonder if you are getting any additional
resolution over, say, a 25 or 50 meg scan. Have you experimented and can
you see the difference on your prints? You may even be losing sharpness by
scanning at too high a resolution. Scanning at a high resolution introduces
softness, which you must then compensate for by sharpening.

But back to your question. Volumes have been written on the topic of 8 bits
versus 16, and I have contributed some bulk to that discussion.

My personal conclusion is that 8 bits per channel is plenty for today's
technology, and the evidence I offer is that (for a gamma 1.8 or greater
image) it is impossible to tell by looking, and looking, after all, is what
we do with photographs.

But there are those for whom that argument is not convincing, and the act of
throwing away any image data is not something they can justify. Whether I
agree with the technical reasons for this extra data, I have to say many of
these people do create better photographs and prints than I do.

So, pick which side of the fence you want to be on. Above all keep your
originals in a safe place - scanners can only continue to get better and
better.

 

[Uni]

Two questions, same subject:

How do you permanently archive your Vuescan files? Do you leave them in the
native TIFF format, or convert them to PSP? Moreover, do you leave them in
the original 16-bit, or convert them to 8-bit to save space?

If you prefer discard critical color information, reduce them to 8 bit.

Uni

 

[Preston Earle]

"Robert A" wrote: "How do you permanently archive your Vuescan files?
Do you leave them in the native TIFF format, or convert them to PSP?
Moreover, do you leave them in the original 16-bit, or convert them to
8-bit to save space?"
-----------------------

I archive 3800x2700-pixel color-corrected images as level-6-quality
(Photoshop) jpeg's. Notwithstanding the current cost of disk space, the
benefit of 95% smaller files (1MB vs. 25MB; 600+ images per CD vs. ~25
images per CD) makes it an easy decision for me. As for "quality" issues
of jpeg's, I don't believe the differences in jpeg's and tiff's is
noticeable at any normal resolution. As for going back to the images to
"improve" them in the future, I'm sure scanners will improve in the
future such that I'll be re-scanning the originals to get significantly
better quality.

For "commercial" images, there may be good reasons to save tiff's, but
for personal images, particularly when there are thousands of them, the
benefits of jpeg's are significant.

There is no visible difference in 8-bit and 16-bit color-corrected
images, so why waste half your disk space?

Preston Earle
(e-mail address removed)

 

[Robert A]

I'm scanning 35mm. I scan based on the intended print size, so for 13x19, I
use 4000 dpi, for smaller prints, I adjust accordingly. I always scan at
16-bit (actually 14-bit with my Canon FS4000US) to a TIFF file.

Once in Photoshop, I adjust levels in 16-bit if necessary, then convert to
8-bit and make all the remaining adjustments for final output in a PSP file.
I know that my Epson 2200 printer only utilitizes 8-bits/channel, so I see
no point in preserving 16-bit data for current prints. But I still retain
the original TIFF file in 16-bit, unretouched or modified in Photoshop for
later archive.

My understanding is that it's important to SCAN in the highest bit depth as
possible, but once you have the file in your computer, there's little if any
use for the extra bits in terms of archiving. Is there any general
agreement on this?

Robert Ades

 

[Kennedy McEwen]

Two questions, same subject:

How do you permanently archive your Vuescan files? Do you leave them in the
native TIFF format, or convert them to PSP? Moreover, do you leave them in
the original 16-bit, or convert them to 8-bit to save space?

Certainly don't even consider PSP as an archive format, it is a
proprietary coding scheme which may not be supported in the future. TIFF
is an open coding scheme which is supported by virtually all image
processing applications and will not only continue to be supported but
continue to develop.

The 16/8-bpc argument continues, but I have yet to see any evidence in
favour of 16bpc archiving, despite Dan Margulis issuing and open
challenge for anyone to demonstrate an image which could be achieved in
16bpc processing which could not also be achieved in 8bpc processing
over three years ago. Given that failure, the generally accepted
principle is to scan in 16bpc, or the greatest available bit depth of
the scanner, optimise the image in terms of gamma and levels before
archiving in 8bpc format.

No doubt such sacrilegious advice will solicit much consternation and
opposing views amongst the collective. ;-)

 

[Kennedy McEwen]

Scanning at a high resolution introduces
softness, which you must then compensate for by sharpening.

On what equipment are you experiencing this particular kind of madness.
Scanning at an increased sampling density may not offer any more
resolution in the image, but it certainly cannot make it any less sharp
or softer!

 

[Robert A]

Thank you.

 

[Hecate]

No doubt such sacrilegious advice will solicit much consternation and
opposing views amongst the collective. ;-)

;-) Only slightly..

I prefer to scan at the highest bit depth possible, do nothing to the
file, and then archive it to either/both DVD and a firewire hard disk.

Then, I work on a copy of that file. It means I always have the 16 bit
file to fall back on should something disastrous happen. I used to
work in computer support and I've seen too many screw-ups which
resulted in original files being trashed with nothing to fall back on.

Anyway, that's my excuse - maybe I'm just paranoid ;-0

 

[Mike Russell]

On what equipment are you experiencing this particular kind of
madness. Scanning at an increased sampling density may not offer any
more resolution in the image, but it certainly cannot make it any
less sharp or softer!

As you approach the Nyquist frequency, certain frequencies are reduced in a
very predictable way. This is softness.

Artificially boosting those frequencies yields a better approximation to the
original image's frequency distribution, and a more natural appearance.
This is sharpening.

 

[Robert A]

But is there any benefit to having a 16-bit backup?

 

[Wayne Fulton]

But is there any benefit to having a 16-bit backup?

Not likely, if it already appears as a halfway decent image.

16 bits may be useful for the extreme tone-shifting adjustments,
like gamma specifically, but histogram B&W Points or Curve too
(the latter is of debatable benefit, but it is popularly done as 16b).

If we are scanning and saving RAW data (no adjustments done), then 16
bits is good, since all of these operations are still to come. This
would be the purpose of 16 bit data.

But if these operations are already generally done (and archive seems to
imply that), then there would be no point of saving 16 bits.
Additional fine adjustments dont need 16 bits at all.

Printers and video are 8 bit devices.

 

[Phil Rose]

I archive 3800x2700-pixel color-corrected images as level-6-quality
(Photoshop) jpeg's. Notwithstanding the current cost of disk space, the
benefit of 95% smaller files (1MB vs. 25MB; 600+ images per CD vs. ~25
images per CD) makes it an easy decision for me.

I think you may have made things "too easy". Such severe compression as
level 6 might be a good choice if all you expect to ever use your images
for in the future is display on a low-res monitor. I surely would not
archive with such extreme compression for images that I may want to use
for printing. Perhaps for 6x4" prints, but then why in the world would
you be making 3800x2700 pixel scans if 6x4" prints was the goal?

As for "quality" issues
of jpeg's, I don't believe the differences in jpeg's and tiff's is
noticeable at any normal resolution.

Not noticeable at what jpeg compression and when standing how far away?
Again, such a statement about "noticeable" ought to be qualified with
the intended use, but even for images merely displayed on a monitor I
believe your statement is a "stretch". It does tend to be true when
comparing tiffs with level 10-12 jpegs, but I don't agree it is true at
all for the level-6 that you stated earlier. Toggle Photoshop's preview
button on/off when selecting various jpeg quality levels--and look at
the changes in the image (at 100%); it should be relatively easy to see
the edge-softening and color/noise artifacts that are generated when
going from tiff (or psd) down to a jpeg quality level of 6.

Phil

 

[Uni]

Not likely, if it already appears as a halfway decent image.

16 bits may be useful for the extreme tone-shifting adjustments,
like gamma specifically, but histogram B&W Points or Curve too
(the latter is of debatable benefit, but it is popularly done as 16b).

If we are scanning and saving RAW data (no adjustments done), then 16
bits is good, since all of these operations are still to come. This
would be the purpose of 16 bit data.

But if these operations are already generally done (and archive seems to
imply that), then there would be no point of saving 16 bits.
Additional fine adjustments dont need 16 bits at all.

Printers and video are 8 bit devices.
http://www.aja.com/kona.htm



Uni

 

[Kennedy McEwen]

As you approach the Nyquist frequency, certain frequencies are reduced in a
very predictable way. This is softness.

This is a contradiction of your earlier statement, since scanning at a
higher resolution (ie. increased sampling density) results in a higher
Nyquist limit and thus, by your latter argument, shifts the onset of
this "softness" to higher spatial frequencies in the image. In short,
your latter argument indicates that scanning at a higher resolution
results in *less* softness, not more, in an image scaled at the same
size! Which argument are you making?

The reproduction of spatial frequencies are reduced by the MTF of the
scanner, which decreases not only as you approach Nyquist, but
throughout the spatial frequency range, usually monotonically from a
maximum at zero cy/mm. Sampling density merely determines where on
that MTF curve the Nyquist limit sits. As sampling density increases,
more of the total MTF range is included in the spatial frequency range
that can be unambiguously reproduced - so more information is resolved,
not less. Clearly this is an issue of diminishing returns, but the
result is always positive - more total detail resolved, not less and
certainly not more "softness". In some systems it is possible to sample
such that the Nyquist limit lies beyond the limiting MTF of the scanner
(eg. most flatbed scanners) thus meeting the criteria for total
elimination of aliasing. In such cases, increasing the sampling density
will not gain resolution, but neither will it increase image softness -
the end result is just more data representing the same image information
content.

 

[Kennedy McEwen]

But is there any benefit to having a 16-bit backup?

That is the $64k question. As mentioned, the general consensus is that
after level adjustments are made there is little point in retaining the
additional bits. As mentioned, the challenge is still out there to
provide examples where this is not the case, but I am not aware of
anyone having successfully done that (though quite a few have tried).

 

[Kennedy McEwen]

http://www.aja.com/kona.htm

I have built systems (monochrome as it happens, but that shouldn't
influence the result) with 12-bit ADCs on the video channel output. The
difference cannot be perceived, but it is something the marketing folks
like to exploit. ;-)

 

[Mike Russell]

This is a contradiction of your earlier statement, since scanning at a
higher resolution (ie. increased sampling density) results in a higher
Nyquist limit and thus, by your latter argument, shifts the onset of
this "softness" to higher spatial frequencies in the image. In short,
your latter argument indicates that scanning at a higher resolution
results in *less* softness, not more, in an image scaled at the same
size! Which argument are you making?

The reproduction of spatial frequencies are reduced by the MTF of the
scanner, which decreases not only as you approach Nyquist, but
throughout the spatial frequency range, usually monotonically from a
maximum at zero cy/mm. Sampling density merely determines where on
that MTF curve the Nyquist limit sits. As sampling density increases,
more of the total MTF range is included in the spatial frequency range
that can be unambiguously reproduced - so more information is
resolved,
not less. Clearly this is an issue of diminishing returns, but the
result is always positive - more total detail resolved, not less and
certainly not more "softness". In some systems it is possible to
sample such that the Nyquist limit lies beyond the limiting MTF of
the scanner (eg. most flatbed scanners) thus meeting the criteria for
total
elimination of aliasing. In such cases, increasing the sampling
density will not gain resolution, but neither will it increase image
softness -
the end result is just more data representing the same image
information content.

Certainly I agree that a higher scan rez extracts more information.

My point is that sharpening is an indispensable step after resampling. That
resampling may be explicit, as when you resize an image in Photoshop, or it
could be implicit, as when a large image is printed at a small size.

For example, the original poster scans to 150 meg - if that is printed at
8x10 without sharpening, it will be softer than an image scanned at a lower
ppi.

I believe this is supported by theory, as I described, and by common
practice in the industry. If you disagree, or if you believe that
sharpening is otherwise not needed, I'm interested in your explanation.