35mm film gamma question

  • Thread starter Thread starter sebif
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sebif

Hi,

I am a newcomer to photography and trying to figure out if the 35mm
film has a linear (like the raw digital format) or gamma corrected
image. Do I need to compensate for gamma after scanning the negatives
(Minolta Dual Scan IV) ?

Thanks,
SebiF
 
Hi,

I am a newcomer to photography and trying to figure out if the 35mm
film has a linear (like the raw digital format) or gamma corrected
image. Do I need to compensate for gamma after scanning the negatives
(Minolta Dual Scan IV) ?

Thanks,
SebiF
Click to expand...
The basic answer is no.

The Scan Dual IV scanner will do a pretty good job of adjusting for the
varying density of Slides. Just check Auto expose for slides in Preferences.

Also check(tick) Auto at Exposure control for negatives.

For Color Negative films, you may need to do a little manual adjustment.
Color Negative films vary from one film emulsion to another.

Each type of color negative film has its own properties. The Scan Dual will
do a very good job, but nothing will make up for how you see the image.

In spite of what people say about color calibration and color profiles, the
final image is up to you.

This is in Preferences under, Color Matching.
If you are using the same color space on the scanner and your monitor, you
should be fine.
 
CSM1 said:
In spite of what people say about color calibration and color profiles, the
final image is up to you.
Click to expand...
Of course it is up to the user. However, calibrating the monitor and
printer makes it easier for me to get what I see.
Jim
 
Jim said:
Of course it is up to the user. However, calibrating the monitor and
printer makes it easier for me to get what I see.
Jim
Click to expand...
The Scan Dual IV has color matching.
 
CSM1 said:
The basic answer is no.
Click to expand...
I disagree. There are two questions here and the answer to one of them
*may* be 'no', but to the other it *is* 'yes'. As a newcomer, it is
true that Sebif probably doesn't need to worry too much about that
distinction yet, but it doesn't hurt to be aware of it, since who knows
how deep he will get into the topic.

Film is not linear, but generally has an 'S' type response rather than a
gamma curve. For example, take a look at the characteristic curves at:
http://www.kodak.com/global/images/en/consumer/products/techInfo/e2328/f0
02_0615ac.gif (watch for the line wrap!).
To all intents and purposes however it is the linear region that we are
mainly interested in reproducing accurately. The fall off at shadow and
highlights is just one of the limitations of film. So the answer to
that question may well be 'no', but there are exceptions.

However, the emulsion density in film is a continuum from the black to
white level. Gamma on the scanned result is required for two reasons.
The first, and primary one, is that it compensates for the response of
the monitor used to display the image, which is typically around 2.5.
This is historical, due to the way that the electron gun in a CRT
operates. However, it turns out that there is a second advantage to
gamma which really becomes significant when using digital media. That
is that the gamma compensation required for the CRT almost matches the
optimum for the response of the eye. Without gamma compensation, much
more of the levels provided by the digital range would be used to
reproduce the highlights than the shadows.

There have been many discussions on this forum on the topic, and it is
dealt with in Charles Poynton's publications, such as:
http://www.poynton.com/PDFs/Rehabilitation_of_gamma.pdf
but the benefits don't really become obvious until you think through the
consequences of Poynton's explanations.

So the answer to whether you need to compensate for gamma is yes - but
the scanner software should sort a lot of that out automagically for you
and it isn't specific to scanning negatives or even film.

You can try to compensate for the 'S' type film response as well, but
generally speaking that isn't necessary unless you are trying to
reproduce the original scene, which is usually impossible in any case,
rather than reproduce the image as recorded on the film.
 
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