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From: "tudor dima" <tudima.nospam@zahoo.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: reduce size of high-quality image
Date: Fri, 16 May 2008 09:07:02 +0000 (UTC)
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Hello everybody,

I suspect Dormant was having in mind the relatively
straightforward phenomena that when decreasing the
resolution in a image-caption device one gets higher
sensibility. This is simply due to the fact that adding N
currents of N transistors will push the signal N times
higher, and more parts of it will lay outside the noise in
the previously darker areas (i.e. below noise threshold).

Once the image is digitized, however, one can only think of
the noise level of the monitor or printer (i.e. pushing the
image above it); simply adding the pixel values will do the
trick, although that would most likely "burn" the highs.
Therefore one has to adaptively compress the dynamic range
of the picture, exactly like ImageAnalyst said.

This could also be interpreted as squeezing a difficult
scene which originally had "8-stops" back within, say 6
stops (therefore printable/viewable), all while pushing the
shadows by S ISO-stops and the highlights by S-2 stops
(where S is a function of the downsampling factor.

The compressing curve, however, ain't no easy trick, I
suspect it should be anti-log. Or one can generate two
images and just cut the sky off the "dark" image and paste
it into the "light" one, as in the good old days of BW
silver-based technology :-)

ImageAnalyst <imageanalyst@mailinator.com> wrote in message
<abbe2799-9dfe-4eaa-b37e-89b02436e73f@d45g2000hsc.googlegroups.com>...
> On Apr 20, 1:52=A0pm, "dormant "
<rod.stew...@uwiseismic.com> wrote:
> > I need to reduce the size of a high quality image, read from
> > a TIFF file.
> > [ ...snip...]
> > Any suggestions for:
> >
> > 1) How to get over the blkproc problem.
> >
> > 2) How to add the precision change.
> 
> dormant:
> You probably realize by now that you misspoke when you
said that the
> averaging process causes an increase in dynamic range, and
you want to
> keep this increase.  In fact, averaging (blurring)
DEcreases dynamic
> range,
> [...snip...]
> Regards,
> ImageAnalyst