Viewscan: now this is a weird one...

  • Thread starter Thread starter Roger Moss
  • Start date Start date
Don: "Not knowing Canon as I mentioned before I can't comment on the
specifics. I can only say that measuring with a stopwatch is *not*
reliable testing. That's no different than looking at an image and
going: "Nah, it's good enough." Again, that's not reliable testing,
you need to look at the (16-bit!) histogram, etc. "

Of course, it's patently obvious if the exposure weren't set correctly
as you'd have blown highlights in slides. You don't need a 16 bit
histogram to see that. The actual exposures can be easily confirmed in
a program like Photomatix which shows the image histograms before you
combine scans at different exposure levels. The histograms clearly
progress rightwards as you increase exposure stops. In this case, VS
is working as it is expected to. The stopwatch merely confirms it. If
you set exposure to 100, you only get the exposure of 6. The
histograms and time taken are identical.
Click to expand...

Well, you answered your own question. In order to confirm the exposure
you had to check out the histograms. So you do "need a histogram to
see that" as you put it. (There's more it than that, of course.)

Also, adding Photomatix to the mix just complicates things further
because you don't really know what it does. When testing one needs to
eliminate all unnecessary steps and (try to) do one thing at a time.

But all that's really a side issue. What I'm getting at is you don't
know what VueScan does internally if you only go by stopwatch alone.
For example, incorrect exposure can go both ways. If this is then
"corrected" e.g. the histogram is stretched *in software* a casual
observer would be fooled. Negatives are routinely stretched both ways!
And so on... So just because the scan takes longer means absolutely
nothing. VueScan may be throwing data away, etc. etc.

That's why an objective testing protocol is needed for any meaningful
tests. Of course, we can do "rough" tests with a stopwatch etc. but
they are not definitive. Depending on the context they may be
meaningless or worse, give a false impression. That's all I'm saying.

Don.
 
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