Roger said:
That reply sort of clarifies things. It seems that we are judging the
program by quite different criteria. I care about the quality of the
final print. Would you mind explaining what you think is important in
a scan, as it's not clear at all. How do you judge the quality of
scans? Just saying "objective testing" isn't an explanation.
I don't want to take sides about VueScan, as I haven't done testing to
check whether what Don says, or whatever is relevant, is true of VueScan
or not.
But let me express some general opinions about "judging criteria". On
this, I basiclly agree with Don: it's the technicalities that count.
That the final result is pleasing, good or what you want to call it does
not, IMHO, say anything about the used programs' qualities -- except
that, of course, when the "technicalities" are very very wrong, the
final result will hardly be too good.
If the answer is: "histograms and programming code" (what a let down, I
thought you had some secret scanner testing software I have never heard
of), those are only interesting to me insofar as they lead to quality
prints. VS gives results in photoshop where the histograms have no
gaps or spikes, unlike a program like Filmget which processes the image
at a depth of 8-bits.
Well, if it scans at 8-bit, that's an obvious limitation of FilmGet.
VueScan scans at 16-bit so there will obviously (*) be more information
in the raw scan, but I see that more as a matter of "input data quality"
than "processing quality".
(*) Of course it's not really obvious, as I have argued with Don a
little about this, as you have read. But let's just assume that
scanners, or at least decent film scanners, do have more than 8 bits per
channel of meaningful information. Under this assumption, of course, a
program like FilmGet that, as you say, only scans at 8 bpc will not even
be considered by someone who wants to get full quality from the scanner.
I have read your posts about needing 16-bit
histograms to see hidden flaws, and about all processing in the scanner
software being "corruption," but unless the scan software introduces
posterization, banding, or other artifacts into my image, I find it
irrelevant to the final quality of the image.
But then you shouldn't even care that FilmGet creates "gaps and spikes"
in the histogram, while VueScan doesn't: it's still "just" the histogram
that we're talking about.
Anyway. Now, Don says that VueScan produces "smooth" histograms because
it deliberately introduces noise.
Let's assume for a moment that it does *not*, and that the smooth
histogram is simply the result of smart processing that minimizes
information loss: what would you prefer at this point, a program like
this, or a program that creates "gaps and spikes"?
And between the "gaps and spikes" creating program and another program
that does not show gaps and spikes because it hides them in noise, what
would you prefer?
Me, I'd prefer the "smart processing" program over the "noise hidden
gaps and spikes" program, and the "noise hidden gaps and spikes"
programs over the "gaps and spikes" program.
That's because the "smart processing" program does what I think it's
supposed to do: is smart enough to discard the least possible amount of
valid information.
The "noise hidden gaps and spikes" is then definitely worse than it, but
it's still better than the "gaps and spikes" program, because it tries,
at least, to process the image so that the loss of information is as
invisible as possible.
All of this is *independent* of final image quality: perhaps the three
programs would all give final images that, for me, are indistinguishable
from one another.
But this doesn't matter. Who knows that, someday, I might not want to
crank the levels on those images, or heavily change the gamma, or
whatever? Won't then the three images differentiate? Surely, after a
point, they will; and at that point, having used the "best" program will
pay.
The final image to be
printed is 8-bit anyway, so if the resultant 8-bit histogram is smooth,
and the image has no visual corruption upon inspection at full
resolution, who cares about the rest?
Smooth histogram doesn't mean much unless you *know* its smoothness
comes from valid information.
For example, imagine a really bad scanner, which has 16-bit A/D but is
so bad that only carries data in the four most significant bits, and all
the rest is drowned in noise.
A scan from it will show a smooth histogram. So...?
Sure, in such a case, there probably *will* be "visual corruption upon
inspection". But even in a case where there isn't visual corrupution,
can you say that it will remain that way upon playing with levels,
applying sharpening, or doing whatever you might fancy doing in a future?
Scanners and scan managers are just tools, so if they produce the
desired result, isn't that what counts?
"Desired"? Desired by whom? I have a thermometer right in front of me.
It shows me there are 22C. Unless it's way off, which it isn't, it
produces "the desired result", I couldn't possibly want more from it.
But, is this an argument against the production of high-precision
temperature measuring devices?
You know, what's "desired" may differ from person to person, and even
change for the same person, depending on various factors.
This doesn't prevent doing a decent, scientific, objective or
near-objective analysis showing that the high-precision thermometer is
definitely, unarguably better than the one I have.
It isn't for nothing that I
start with good quality prime lenses on a sturdy tripod with 100 speed
film, scan at the native resolution of the scanner and output to a Fuji
Frontier. If the scanning program were incompetent, it would clearly
be the weak link in the chain that keeps the good inputs from leading
to a correspondingly good output. This isn't the case.
Then perhaps Don is wrong about VueScan. This, however, takes nothing
away from the value of scientific testing.
Please make the case for why whatever you mean by objective testing is
preferable to subjective judgement about the quality of the scans.
Simply saying it is inherently superior isn't going to convince anyone
of anything.
Oh well, it convinces *me*.
Since the "subjective" judgement is subjective, I'd rather make the
relative processing myself, i.e. in Photoshop or something.
I'd like the scanner program to do the "objective" part for me, though,
and do those things like adjusting for film curves, setting exposure
times, even sharpening (if the scanner's exact need of sharpening is
known), in a mathematically as exact way as possible -- and losslessly.
by LjL
(e-mail address removed)
