Photo System Engineering I, the fundamentals

[Photo Engineer]

Originally Posted by Craig

Out of curosity then, why was Kodak's first colour material (Kodachrome) a positive material? Why was positive material even developed at all? Wouldn't it have made more sense to have made a negative film only?

There are many factors in this to consider.

First off, the drive was on for a color motion picture film. Second, reversal such as Kodachrome was the only way to get color in the early days. The problem of placing the image forming materials into the emulsion had not been solved yet.

However, Kodak and Agfa both produced negative color films as soon as possible along with print materials and these became the norm for both still prints and for motion picture as well due to the ease of reproduction. Positive to positive printing degrades image quality very rapidly and the images take on what is called in the trade "a dupey look".

The color negative films were produced just a few years after the introduction of Kodachrome, as soon as the problems of incorporating the color image formation materials into the emulsion were solved. At this point, both Hollywood and the amateur quickly abandoned reversal imaging materials. The exception was Technicolor which came and went over the years. Even so, it was duped using a negative material.

PE

[Krockmitaine]

Originally Posted by mhv

I urge anybody in proximity of a public library to look for that article (and read the whole encyclopedia as well!). It is a great complement to PE's article, and will help in providing you with a good vulgarized background on image tone management.

Hummm, we don't have it here
Let's hope for a donation, we received a Kodak book not too long ago.
(Yes, I tried to add it into my collection but it was too late as it was cataloged)

Marc

[AgX]

Originally Posted by Craig

Out of curosity then, why was Kodak's first colour material (Kodachrome) a positive material? Why was positive material even developed at all? Wouldn't it have made more sense to have made a negative film only?

Also Agfa who solved first the `Fischer-problem´ of incorporating couplers into the very layers, and who were quite surprised when Kodak presented their Kodachrome film while they were still working on a solution of the problem, started with a reversal film.
-) One driving force for them was surely motion film for cinema use. As a lot was worked on that topic then. And the most practicable way of doing would have been a neg/pos-system. (Though even a single reversal film would reduce hassle in the camera and could be copied into any other system for cine-projection.)
-) The coming of Kodachrome put them under even more pressure and as furthermore they got the impression that Kodachrome patents would block them the reversal way it was decided to go the neg/pos-way.
-) However a few months later this was revised as one thought to show up with something as soon as possible. That meant 35mm film for still-photography.
-) It took about two further years to establish a working neg/pos-system (still film/film, no paper yet).
-) It took even longer to decide the Agfacolor neg/pos system to be the future Cine standard.

From the Agfa perspective the decision between reversal and neg/pos was less a principle one but rather one of resources and time.

[Photo Engineer]

Agfa neg-pos with a print paper was a goal of Agfa from the earliest days, as the paper print could be handled and shown. The earliest formulas for paper show that it was merely a diluted form of the film coating.

I'll try to cover more of this when I get to color though.

PE

[monkeykoder]

Originally Posted by Photo Engineer

For mathematicians out there, the curve generated by all photographic materials is a cubic spline.

PE

Not that it really relates to the topic at hand but a cubic spline is a method of approximating functions is this what you meant or was it that the curve was in the form of a cubic function?

[Photo Engineer]

The curve is not a cubic function AFAIK. It is more that the spline is used to fit, or approximate, the functions of photomaterials which include toe, mid scale and shoulder.

The first derivative is, of course the slope, and when you multiply the instantaneous slope of a film curve by the instantaneous slope of the paper curve gotten at a given exposure, then you have the instantaneous slope of the print you obtain.

This is only approximately true for B&W materials, but deviates in color unless you read analytical rather than analog densities. Then you need to add in to the mix, a 3x3 matrix of the dyes.

You can easily see how complex this becomes and why we used so much computation power in our work. Probably more than you wanted to know. But, I hope it helps.

PE

[monkeykoder]

More than I want to know does not exist...

[Photo Engineer]

Originally Posted by monkeykoder

More than I want to know does not exist...

Ask then.

PE

[monkeykoder]

I think I'm going to have to pick up a Gen. Chem. book before I have any more questions...