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Contradiction over how to achieve saturation


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#1 Christopher Wedding

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Posted 29 July 2008 - 11:09 PM

Hi guys,

There seems to be a divide on here whether over-exposure slightly
increases the saturation of colors or decreases. Some of the posts I've
read on here say increase and others say the exact opposite. However,
both sides have people I believe to be pros saying it.

So which is it?
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#2 Satsuki Murashige

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Posted 30 July 2008 - 02:09 AM

Are we talking about negative film or reversal film?

With negative film, more exposure means more grains of silver halide crystals get exposed on the emulsion. In the development process, the unexposed silver halide grains get washed away, leaving the exposed metallic silver which forms the image. (Color negative is a bit more complicated in that the exposed silver also gets washed away, but not before triggering a release of colored dyes on each color layer of the emulsion which forms the image).

But in either case, you are left with a certain amount of image-forming grains on the processed negative. With an underexposed negative, you will literally be left with fewer grains since the greater number of unexposed grains have been washed away. That means there's less information on the film - color, sharpness, and contrast all take a hit. Conversely, more exposure means there's more information on the film - color, sharpness, and contrast increase. That's why an overexposed negative is often referred to as "dense" or "thick" and an underexposed negative is referred to as "thin" - one is packed with information and the other has very little.

Reversal film works in the opposite way because it goes through a two-step development process. A negative image is formed on the emulsion and developed. Then a negative of the negative is formed during another processing step, resulting in a positive image. I don't understand the process fully, so that's the best I can explain it. But the end result is that a "dense" positive is achieved by underexposing and a "thin" one is achieved by overexposing. Again, the dense positive has more information in it, and thus more color, sharpness, and contrast. Keep in mind that reversal stocks already have more contrast and color saturation built into them than their negative counterparts because they were originally intended to be projected directly, while negatives were meant to be printed on high contrast print stocks. So you can generally achieve a much more color saturated image with reversal stocks than negative stocks.

Another way to get more color saturation is to push, or over-develop the stock at the lab. While pushing can't add any more information to the exposed film (how can it, when the image has already been formed?), it can increase the density of the grains that have already been exposed. So that's why you get more color saturation but also more "visible grain" by pushing, because part of what we perceive as "grain" are really the black gaps left by the unexposed silver, which has been washed away in development. The larger the gaps (i.e. the more underexposed the footage is), the bigger the "visible grain."
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#3 David Auner aac

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Posted 30 July 2008 - 02:36 AM

Satsuki, what should we add to that? It's such a complete answer, it should be made into a FAQ topic!

Regards, Dave
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#4 Satsuki Murashige

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Posted 30 July 2008 - 02:47 AM

Satsuki, what should we add to that?

Well, how about increasing color saturation through printing or other processing techniques, like the now-defunct Technicolor IB printing, cross-processing, etc.? I'd like to hear more about that...
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#5 David Auner aac

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Posted 30 July 2008 - 02:59 AM

Well, how about increasing color saturation through printing or other processing techniques, like the now-defunct Technicolor IB printing, cross-processing, etc.? I'd like to hear more about that...


Hehe, true that. I'm sure David could elaborate on that. But I still think that a couple more FAQ or stickies would be a good idea to avoid newbies posting the same stuff all over again!

Cheers, Dave
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#6 Jonathan Bowerbank

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Posted 31 July 2008 - 05:11 AM

There seems to be a divide on here whether over-exposure slightly
increases the saturation of colors or decreases.


There is a level of overexposure in film where you start to lose detail, and that's where you begin to have less "color saturation" in your image. I performed a test once using Storaro gels. At about 2 - 2 1/2 stops over, the image was fine, nice grain, etc. But that seemed to be the threshold. Once I got to around +3 stops, colors were a bit washed in my opinion.

The perception that there is more color saturation when you underexpose, I think, has a lot to do with the increase in contrast that is achieved when you do so. In the aforementioned test, the underexposed footage looked gorgeous with a lovely contrast of colorful light & shadow, which made the color all the more striking.

Watch a lot of Christopher Doyle's work with Wong Kar Wai. In a lot of those Hong Kong underground scenes, there's a lot of colorful lighting and the image is noticeably underexposed just a bit to really accentuate that contrast between colorful light and shadow.
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#7 Christopher Wedding

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Posted 31 July 2008 - 10:05 PM

Thanks Satsuki,

I appreciate the detailed answer. I totally agree.

However, there are definitely posts on here that inisist overexposure on negative decreases saturation (Not the extreme Jonathan mentions) and I was hoping someone would respond to that.

Hey Dave, I know there are simlilar posts out there. That was the point...there's contradiction in the
responses in those posts.

Cheers,
Chris
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#8 David Auner aac

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Posted 01 August 2008 - 12:40 AM

Hey Dave, I know there are simlilar posts out there. That was the point...there's contradiction in the responses in those posts.


Hi Chris,

I wasn't really referring to you, I just thought it was a good idea to make more stickies with FAQ and respective answers as we currently have a large influx of new members all asking the same stuff more or less.

Cheers, Dave
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