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[filmscanners] Re: Dynamic range question



When you scan negative film, the histogram is narrow. So I would say
negative film has a low dynamic range.[Yeah, I know slide and negative
film is really the same.]

I think I see the confusion here (or specmanship). The dynamic range of
a dataconverter is related to the number of bits, since the smallest
signal the dataconverter can resolve is 1 lsb out of 2^N bits. The
dynamic range of the CCD spans from the  point near where it saturates
at maximum brightness to where the photons are lost in the noise.

When you scan negative film, the dynamic range of the film is narrow.
However,  you expand this dynamic range during the inversion process to
restore the contrast in the final image. If the negative film only uses
1/4 of the range of the scanner, then you would expand the range by a
factor of 4 before truncating the image to 8 bits (which is all the eye
sees). Thus you really need a 10 bit scan to get 8 bits out. Using more
bits during the scan of slide film doesn't buy you nearly as much as you
probably aren't going to increase the overall contrast in the final product.

Here is where Astia 100F comes in handy. It is a bit less contrasty, so
you do expand the contrast in the final product, due it tends not to
span the limits of the scanner.. I never projected or printed Astia, so
it may not look as vivid due to the lower contrast, but it does scan easier.

Berry Ives wrote:

>Austin, with respect to your last sentence, isn't the point really that the
>contrast range of negative film is greater than slide film?  What I mean is
>that you can lose either the shadows or the highlights, but slide film
>requires more precise exposures and is more limited in the range that it can
>handle.  Where I live and shoot, there is great contrast (high elevation
>southwest desert), and I think that is one reason for me to shoot negative
>film.  I never lose either end that way with the great latitude of negative
>color film.  But I'd like to hear what disadvantages there may be to this
>approach, if any, in my situation.
>
>Still waiting for the right DSLR for me...
>
>Berry
>
>
>
>On 3/25/05 4:45 PM, "Austin Franklin" <austin@darkroom.com> wrote:
>
>
>
>>Hi Bill,
>>
>>
>>
>>>It's been several years, but I seem to remember that when I got my
>>>Nikon 4000ED filmscanner they were claiming a Dmax of somewhere
>>>around 3.5 to 4.0, but I measured it (by scanning a Kodachrome IT8
>>>target slide and examining the greyscale separation)  at around 2.1
>>>to 2.9 (don't remember the exact number).  This kind of disparity
>>>between manufacturer's claims and real-life performance is the rule,
>>>not the exception.
>>>
>>>
>>>From what I can tell from your post, what you did was measure the density
>>>
>>>
>>range of the IT8 slide, correct?  If so, then that is what you measured, the
>>density range of your IT8 slide...that may or may not equal (or closely
>>equal) the dynamic range of the scanner, they are two different things, and
>>are not necessarily a 1:1 correspondence.  That is a whole can of worms unto
>>it self.
>>
>>It is true, that typically manufacturers who make claims of 4.8 are simply
>>stating the bit depth of their A/D converter, and their A/D converter is 16
>>bits (log 2**16 is 4.8).  As has been said, the dynamic range (and density
>>range) of the scanner is typically limited by the CCD, and not the
>>electronics.  Manufacturers of CCDs do publish the noise numbers of their
>>sensors, and if you could find out what sensor they are using, you could
>>find out from the sensor's specs what the manufacturer claims the range is.
>>
>>Also, unless you are scanning slide, the dynamic range/density range of the
>>scanner will not be prohibitive for most any modern scanner.  And, for
>>negative film, it has nothing to do with being able to "pull out the
>>shadows", as the shadows on negative film are the light areas, not the dark
>>areas.
>>
>>Regards,
>>
>>Austin
>>
>>
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>
>
>
>
>
>

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