Film color balance

benjiboy said:

Fuji Pro 160 L (NPL) is a tungasten balanced C41 Negative film available in 120, and large format sizes, I've shot loads of it in the studio with hot lights fairly recently.

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Is that product current? I don't see it listed at either Freestyle or B&H, at least not in 120 format. (I didn't check LF sizes.)

srs5694 said:

Is that product current? I don't see it listed at either Freestyle or B&H, at least not in 120 format. (I didn't check LF sizes.)

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No nor is Portra 100T. Both were good films I preferred NPL in mixed lighting over 100t, but 100t did a much better job with shadows and actually was faster if you were exposing for shadow detail. To do the same as these films you would need a daylight film that could take a 2 stop hit in speed.

In pure technical terms, it is incorrect to state that colour balance is adjusted in digital by changing the "gain" of certain colours.

There is no such thing as "adjusting the gain" in a RAW file. What was captured in the RAW file ain't gonna change in post-processing. Of course, one can call "gain" the process of changing the d/a curve of a given colour. That doesn't make it true gain, in the electronic sense.

And digital cameras don't change the gain of the individual sensels of any colour pattern under the Bayer filter when changes are made to the white balance. What they do is change the curve their native processor applies to the RAW file to produce the sampled jpg. Very much like one does when processing the RAW file in an image editor.

Of course, this curve adjustment does not come out of thin air. Typically one gets increased noise in the given colour when "increasing the gain" of that colour. And "holes" in the histogram, as well.
But when done in moderation, the result is the equivalent of "increasing the gain" of the capture circuits by electronic means.

With film, one can actually "increase or decrease the gain" during development. It's called "pushing" and "pulling". What usually can't be done is to do so for each colour. One has to push or pull the whole emulsion, all three base colours. Speaking of colour film, of course. And that's one of the reasons why correcting the colour balance via development is very hard or simply impossible.

Of course one can compensate more or less at print or scan time, using essentially a similar technique to adjusting curves in digital cameras. But once again the diminishing returns come up: one cannot create something out of nothing. Grain and other noise effects will usually kick in.


Much better to get it right in camera, in both film and digital!

srs5694 said:

Is that product current? I don't see it listed at either Freestyle or B&H, at least not in 120 format. (I didn't check LF sizes.)

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It must be a couple of years since I used it, I checked Fuji UK , and I don't think it is any more.

Well after having read up more on it, the real difference between film and digital in this respect is the toe and the shoulder in film. You can adjust film in post just like you can with digital but the non linear portions of the curve will not balance out. When I get home I'll make up some quick plots that demonstrate this.

As far as digital, gain isn't the right phrase side you are right, it is done after the fact, non electronically. It's just a multiplicative factor applied to individual cameras. However the sensitivities of the channels digital sensor are preset. Changing the white balance before or after the shot does not change these relative sensitivities. All it does is apply a multiplicative factor to the channels to get the right color balance.

Tim Gray said:

Well after having read up more on it, the real difference between film and digital in this respect is the toe and the shoulder in film.

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There is also, at least with negative films, a significant difference in the brightness range that can be dealt with.

C-41's latitude, in this respect, allows the shooter to "place" exposures creatively in relation to the toe and shoulder. This is not normally a technique that digital systems can mimic without resorting to HDR processing.

This extra latitude can be used to get better color balance and to reduce grain in the shadows when printed by allowing better exposure of the weaker color channels, getting them off the toe, without pushing the stronger channels on to the shoulder.

markbarendt said:

This extra latitude can be used to get better color balance and to reduce grain in the shadows when printed by allowing better exposure of the weaker color channels, getting them off the toe, without pushing the stronger channels on to the shoulder.

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This makes sense to me, and though I've never tried it, I could see how it would work. However, it seems to me, depending on the number of extra stops needed to push the blue 'channel' up off the toe, you'd probably be better off with an 80A filter.

It's a shame higher speed tungsten film is no longer made. I would love it if Kodak made an equivalent to its Vision2 (or 3) 500T motion picture stock for still camera use. I'm unfamiliar how well Portra 800 fares in tungsten lighting...

Tim Gray said:

This makes sense to me, and though I've never tried it, I could see how it would work. However, it seems to me, depending on the number of extra stops needed to push the blue 'channel' up off the toe, you'd probably be better off with an 80A filter.

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Using a filter is still a good idea, my post was just addressing the difference between digital and C-41.

When using a filter you have even more practical latitude because the exposure of each level will be closer to each other. Instead of three disparate humps they would overlap better.

What this boils down to is better shadow detail.

Theoretically the 800 speed Portra could be shot at EI 200 to make up for the 80A on an un-metered camera or with a hand-held meter. With TTL metering this is a non-issue, the camera would make the correction.

markbarendt said:

Theoretically the 800 speed Portra could be shot at EI 200 to make up for the 80A on an un-metered camera or with a hand-held meter. With TTL metering this is a non-issue, the camera would make the correction.

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I haven't done a lot of shooting with 80A filters, but I have done some. I've always found that the results are a bit underexposed when I use TTL meters (mostly on a Fujica ST801). I'm not sure why that is, though.

It just sucks that a nice film like Portra 800 is reduced to a 200 speed film with the proper filter for indoor use. I wish someone (still) made a high speed tungsten film. Even if it was 400...

Just cut down some bulk fuji eterna.


And film can be colour corrected, in as far as given the captured range you can make it look like anything you want it to look like, as is done with a digital intermediate with motion picture films, though if you should daylight film in tungsten without colour correction gels on the lights (or at least a filter on the lens), you're either going to overexpose or underexpose part of the film.

And many negative films have 4 layers (fuji).

Once digitised, the channels are discrete, as they need to make up the scene with the same colour more or less you'd get from a print, it's also possible to reverse engineer a tone curve.

It's not to say it's without problems, here is some Colour Balanced Pro 400H (120)