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

[P3D Don Chaps <dchaps@xxxxxxx>]

I wrote a long answer to this, then cancelled it as silly. My point was 
that in using a negative material there is a third party changing the 
color balance in an unpredictable way.
	Take a wall in open shade with peeling paint of varying colors. Take 
a negative of it. Send it to three different minilabs. The resulting 
three prints will not match in color, no matter what light source under 
which you view them. Use a standard ANSI color balanced viewing box, if 
you want, the three prints will not match.
	Stand in front of our friendly local wall. Take three rolls of slide 
film. Send it to three different labs. The three slides will match, no 
matter what light source you use. Use an ANSI standard color balanced 
light table, if you want.
	I mentioned Grand Photo because the owners are 3D photographers. 
When they print, they make sure your left and right views match. In my 
experience, to get a local minilab to take the same care (small prints 
are a low profit item), you need to find a friendly lab and take along a 
Viewmagic to show them why you need prints from two rolls of film to 
match.
	If you want a duplicate print, and quality matters, you should 
supply your original print to the lab as a "match print." If you don't, 
your original and the new print will probably not match. There will be 
differences in the color balance. No matter what light source under which 
you view these prints, they won't match. Our eyes may be able to 
accommodate a large range of color temperatures of light as light 
sources, but we are excellent about determining subtle differences of 
color when samples are side by side. 
	Finally, people do care about the color balance of slide film. It's 
not unusual for a professional to buy many rolls of the same lot#, test 
and determine exact exposure index and color balance, freeze or 
refrigerate to retard the aging (professional film is usually seasoned 
before packaged). Then the photographer has a known quantity. Large 
format color slide film sometimes comes a small correction sheet for that 
batch containing a correction to the film speed and a recommended 
starting filter pack.
	One wouldn't go to all that effort for negative film because the 
variables on the printing side are unpredictable. Your best bet to reduce 
the variables in the printing is to use a known item in the first frame 
(such as a grey card, a fleshtone will be an adequate substitution) and 
ask the printer to correct for the first frame and lock the settings for 
the whole roll. This only works if the whole roll is shot under the 
conditions of the first frame.
	I hope makes what I meant more clear. If not, oh well, I'll just go 
climb in the fridge with my film.





On Mon, 9 Sep 1996, P3D Andrew Woods wrote:

> Don Chaps <dchaps@xxxxxxx> wrote:
> > Good slides can be made from negatives if you use a film designed for 
> > that purpose. The problem that would stop me from doing that on a regular 
> > basis is the color balance problem. Unless you pay big bucks for a pro 
> > job, the slides will be the positive equivilent of minilab 4x6s. Getting 
> > the same exposure and color balance on each of your stereo pair would be 
> > the problem. If you make 
> > prints you sometimes have to browbeat the printer to get matching prints 
> > (Grand Photo is the exception. They make it painless). 
> > If you were going to make an edition of slides, it would be worthwhile to 
> > go to a professional output bureau, negotiate the color balance, and put 
> > the time necessary to get great results. 
> > 	I think the reason that color slide film is used widely 
> > professionally even with its disadvantages of higher contrast and limited 
> > exposure range is because the color balance is fixed and not subject to 
> > interpretation by an unknown third party.
> 
> The reason you don't need to colour balance your slides is because your
> eyes do the job for you - yes, your eyes can perform colour balancing!
> Slides are usually viewed under certain distinct circumstances - projected
> large in a darkened room or viewed through a viewer.  In both of these 
> circumstances, the only thing your eyes can see is the slide image.
> The eye's colour balancing works over the eyes entire field of view.
> In the above circumstances, the slide is the eye's only stimulus therefore
> the eye performs colour balancing of *ONLY the SLIDE*.
> 
> 4x6 prints on the other hand are viewed quite differently.  you hold them in
> your hand and the print only fills a very small proportion of the eye's
> field of view.  The eye's colour balance will therefore be weighted heavily
> on your surrounds.  prints therefore NEED to be colour balanced by the lab
> because you will easily notice when their colour balance is wrong.
> 
> 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.
> 
> Now let me hypothesise a little: 
> Consider if slides were viewed in a different manner - say with a hand
> held unit where the slide was back projected onto a 4"x6" screen.
> The image on the screen would look just like a 4x6 print but the image
> comes projected from the slide.  
> Now would you notice the colour balance problems in your everyday slides
> from your 35mm camera?  Based on the criteria discussed above I would
> think yes, but there are other factors involved which further complicate
> the issue.  
> A print is illuminated by the same ambient light which lights the room.
> In the unpatented Woods viewer model A mentioned above, the slide image
> is lit with the colour temperature of the projector bulb which is 
> different from the room lighting...
> 
> 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?
> 
> +------------------------------------------------------------------+
> |  Andrew Woods   | Centre for Marine Science and Technology,      |
> |                 | Curtin University of Technology,               |
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