Re: slide colour balancing (was re: APS and 3D slides)

[P3D William Carter <wc@xxxxxxxxxxxxxxxxxxx>]

Film records a limited range of information. The range of display is far 
narrower than our ability to see. 
It is a prime technical objective to preserve as much information in the 
three color dye layers as possible. 
For a standardized development, a film's color balance defines the 
median exposure (18% grey) for each dye layer for a specific color 
balance. 
Exposure by other than this specified 'white' balance will cause the dye 
layers to saturate at different rates and at different levels from each 
other. This will result in the distortion of any 'real world' 
documentation of a scene.

Andrew Woods proposes:
>The eye's colour balance will (when viewing prints) be weighted heavily
>on your surrounds.

>SLIDES on the other hand don't need colour balancing because under 
>normal circumstances the eye adjust to the slide's colour balance and 
>you won't notice the error in colour balance.

An interesting point. One may not notice an error in color balance. But, 
at the very least, the already over challenged film will be losing 
information. And, whether perceived or not (because the original scene 
is not there to contrast with the image), the relationships between the 
colors will be distorted.

>If the colour balance of a slide was very bad I can imagine a need
>to correct it.  BUT is there anywhere which does this and does
>anybody actually do it?

In motion picture work a great deal of effort is spent 'timing' the 
color balance. This is mostly done to maintain balance between the 
various shots in a single scene. In fact even the camera lenses are 
matched with this in mind. In this sense, each scene becomes the 
"surrounds" for the next. But, to answer the question, yes. 
Films, for example, are also balanced for release distribution. They are 
designated either for carbon arc (warm) or xenon projection. Your slides 
are processed for tungsten projection unless you specify xenon.



-- 
                wc@xxxxxxxxxxxx
    37deg 39.09'N x 122deg 29.56'W x 90'MLLW





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