Digital negative

Started Feb 1, 2013 | Discussions thread
sherwoodpete
Veteran MemberPosts: 7,759
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Re: Film and digital more similar than you think
In reply to blåland, Feb 3, 2013

blÄland wrote:

rpenmanparker wrote:

As you can tell from my prior responses to this idea, I am no expert on the subject. But I was just thinking about what is positive and what is negative re: sensors and film as regards a final printed image. Please follow my logic:

In either film or digital first think of a unit area as a box to contain something, silver grains in film and "check marks" representing photons observed by the digital sensor. Now you expose. The film box fills up with silver grains; the digital box fills up with check marks. In both cases no light at all results in the null set in the box. No matter how much light you supply, the chemistry of the film and the design of the digital electronics both limit the amount that can be recorded. There is only so much silver halide to be converted to so much silver and so many checks that can be recorded. So while chemistry is different from electronics, and the effects don't look exactly the same, clipping of highlights is a natural effect of both systems. So far both systems are performing the same function whether that you think of it as positive or negative.

Now you print. A film with more silver grains in the box produces a paper image with fewer silver grains in the corresponding box on the print. We think of that as an inverstion. But similarly the digital file containing more check marks in the box produces a prints with less ink density, i.e. fewer IJ droplets in the corresponding image area or box. In both cases more is converted to less, i.e. the image is effectively inverted.

So from the more gives less point of view both systems are "negative" systems that require inversion to produce a printed image. The most light finally translates through a pair of processes to less silver or less ink. Pure white means the photo paper itself with nothing on it in both cases, not a lot of something on it. That would be the monitor display image, corresponding to slide film. But that is another thought experiment.

I can't say that this has any bearing on OP's proposal, but I found it startling.

Robert

Yes I understand your reasoning here. But don't fully agree, (I guess it's clear now that I'm no expert either). This was not meant to be a film vs digital argument, but you do have a point in comparing them.

Here is a proof, of sorts.


This image is taken with my old Canon F-1 and a roll of fuji extra 400. The last frame was accidentally exposed 12-14 times. Normal shots. Still there is a lot detail left. This is probably not possible with either positive film or digital. Also there was this guy on this forum that recently posted an imaged that had been exposed 36 times by accident, but even then there was discernable detail left. I tried to find that post with no luck. He wrote that the negative was all black and that the paper copy took several minutes to expose.

The foveon sensor would compare better to film but is still far from it.


Interesting sample image. This happened to me once, when I exposed about 36 shots on a single frame, and yes, there is still some detail there.

But, 36x is about 5 stops overexposure. Or it would be if the same subject was shot each time. But in practice the highlights of one shot may fall in the shadows of another, so it's a bit less. 14x is about 3.8 stops overexposure.

I'm not sure that these results demonstrate  the difference in dynamic range. Mostly the comparison points us to the fact that it isn't actually possible to do a straight comparison with an ordinary digital camera. If a separate mechanical shutter was attached to the front of the lens, and the camera's own shutter held open for a prolonged time it would be possible, but this isn't something which most people would be in a position to test for themselves.

Regards,
Peter

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