Re: [APML] More SS4000 scanning questions

["Carlos Milovic F." <cmilovic@yahoo.es>]

Hi Alan

I will desagree from some thoughts that were explained
early... let's go step by step.

> 1. I notice so far in his examples, that he has
> color management 'off'.
> Is there a reason for this?
> 

You should avoid color management with your raw scans
becouse that will change the values of the pixel when
it will be readed by PS or another IP (image
processing) software. Of course that color management
can be exploided just for displaying purposes, but i
think that the raw data is so precious that we must
preserve it as much as we can (save it directly to a
cd or dvd, for example). Anyway, if you don't color
manage the file, it will be assumed that it is in the
sRGB color model.

> 2. When I scan and save 'raw' images, the dialog
> indicates that it is a
> 12 bit image. I had hoped for 16 bits. What goes?
> 

The SS4000 scans your films with a 12bits accuracy in
the tonal range, so that's the true final amount of
gray levels (for each channel) that you will see.
Becouse TIFF archieves supports only 8, 16 or 32 bits
per channel, the scanning softare fills the other
4bits with zeros. You can easily see that in
PixInsight. Open the image's histogram, and view it at
12bits precition. The histogram function will look
nice, but if you change to 14 or 16bits, you will see
a lot of gasps in there.


> 3. To save time when scanning lately, I have not
> been doing pre-scans.
> I simply do the full res scan and go to the next
> one? Is this OK, as
> I'm scanning and saving untouched 'raw' images?
> 

If you are doing raw scans, the results are just the
same. The data is saved as the CCD reads it. That is
exactly what I do with my scans, and it works very
well, and saves a lot of time. BTW, you can speed
things a bit more by doing the scanning with the
thumbnails interfase intead of the preview/scan one.
You can scan the whole set of slides/negatives with
just one operation.

> 4. I've asked this before and the answer made sense.
> For 35mm color
> negative film, is a scan setting higher than 2700
> dpi useful? I had
> someone tell me in an off-topic discussion on the
> Losmandy group that I
> should be scanning at the highest resolution,
> 4000dpi in this case.
> 

Yes. Scan always at the maximun optical resolution of
your scanner. It is always better to do that, becouse
you can push the digital processing much more. The
noise introduced by the scanner will be much smaller
than the real features, so it will be easy to delete.
You can perform deconvolutions, multiresolution
analysis and much more more easyly... and finally, the
data will "tolerate" much more the processes applied
without introducing artifacts. In fact, I remember
that many planetary imagers (with webcams) oversample
the image 2x for the same reasons.
Anyway, becouse a 32bits 4000dpi scanned RGB image
(35mm) weights nearly 250MB, I don't recommend to you
oversampling, and just work it directly at maximun
true resolution.

> 5. In a related question, should slide film (E200)
> be scanned higher
> than 2700dpi, seeing as it has higher contrast?
> 

Of course! I scanned 4 Provia 400F (pushed +2) first
with a SS35 at 2700dpi, and a few months ago with my
SS4000 at 4000dpi, and the changes were evident. Now I
was able to recover more data, and to reveal features
smaller than the first try. The noise reduction was by
far more easily, and I was able to increase the
contrast much more. Of course that the 8vs12 bits
helped a lot, but the oversampling played a key role
too.

> I'm sure there will be more later, thanks in advance
> for your comments.
> 

If you are running for the gold, always more
resolution at the beggining is the best choise (and in
the IP software too). As the first statement of
digital IP says: always try to get the best raw data
to start with.




=====
Regards,

Carlos Milovic F.
-------------------------
Astro & Photo - CMF
http://www.astrophoto.vze.com
-------------------------
Visita "AstroFoto", el foro de astrofotografía en español
http://espanol.groups.yahoo.com/group/astrofoto


		
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