Digital BW, The Print

Has anyone taken the output of a 16 bit scan saved in 16 bit tiff and 
then read into a software package like Mathematica or Matlab so that you 
could actually see what was going on?

If not I may give that a whirl.

Truman

Martin Wesley wrote:

> ----- Original Message -----
> From: "Austin Franklin" <darkroom@...>
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Sent: Friday, October 11, 2002 10:15 AM
> Subject: RE: [Digital BW] Re: 'combed' histograms in 16 bit ?
>
>
> > Can anyone explain why it would even be any different?  It should be the
> > exact same data...and as I said, the histogram is an 8 bit histogram, no
> > matter whether the file is, 8 bits or 16 bits.  When displaying a 16 bit
> > file, the low 8 bits are simply ignored...and when converting a 16 bit
> file
> > to 8 bits, simply the lower 8 bits are dropped...so they should be the
> same?
>
> Austin,
>
> I am still trying to get a better grasp on what is happening with the data
> during scanning and mode changes. So see if I am correct in the following.
>
> As an example lets say the scan originally came from a 12-bit scanner and
> the 12-bit data was mapped accurately into 16-bit space (each 12-bit 
> value X
> 16) so that in 16-bit space there are pixels at intervals of 16 levels or
> tones. If you did a strong levels or other adjustment on this 16-bit file
> wouldn't the spacing change so that in some portions of the 16-bit range
> data points are brought closer together, even overlapping giving the
> "spikes" seen in histograms, and in others portions of the 16-bit 
> range they
> are spread farther apart than intervals of 16. To see a gap in the 16-bit
> file, 65,535 levels, with an 8-bit histogram tool it would have to be 256
> 16-bit levels wide, which sounds like a lot, but I guess you could 
> push the
> data that far.
>
> Assuming you had a "perfect", full range, 12-bit scan there would be 4096
> tones in the original 16-bit scan but after manipulation it might be 
> reduced
> to a lower number. It is still going to be much more than 256, so when you
> do a mode change to 8-bit wouldn't be likely that in mapping and throwing
> out tones that the gaps get totally or partially filled in so that the
> histogram of the 8-bit version of the file looks smoother?
>
> Of course there is the question of whether the Histogram function in
> PhotoShop reads 16-bit and 8-bit files the same way.
>
> What I would love to see on the Histogram display, which does not seem 
> like
> it would be difficult, is first the bit depth of the file being 
> analyzed and
> a display of the number of discrete tones or levels in the file. This last
> would be a great help in determining the amount of data loss caused by any
> adjustment or action.
>
> In the end though a lot of this may not matter for practical purposes 
> since
> you can often get good prints from 8-bit files with rather nasty looking
> histograms. Degradation in the histogram of a 16-bit file may be even more
> irrelevant.
>
> I suspect that Frank has run into something Tyler Boley and I have
> encountered with SilverFast software. There are certain workpaths that 
> will
> produce a 16-bit file with a nice looking histogram after scanning but 
> that
> immediately look degraded after the first adjustment.
>
> Martin Wesley
>
> >
> > On the bottom of the histogram you are looking at the 16 bit file on,
> isn't
> > the scale 0-255?
> >
> > Austin
> >
> >
> > > Andrew,
> > > I duplicated the 16 bit file and converted to 8bit - then compared
> > > the histograms - you are right there is less combing viewed in 88
> > > bit - but it's still there albeit not quite as bad as in 16
> > >
> > > ?
> > > Frank
> > > > > after minor contrast adj in 16 bit scans (moving the end sliders
> > > to
> > > > > the edges of the histogram & the middle to fix the mid tones), I
> > > > > still have 'drop out' or combed histograms - any ideas, tips ?
> > > >
> > > > Convert the file to 8 bits THEN look at the Histogram. You should
> > > see NO
> > > > combs.
> >
>
>
>
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