color internegatives?

I understand that color negative has that orange mask. However, consider for a second that it didn't; that you had a color negative film that was normal except for it didn't have the orange mask. If you rephotographed a color negative onto color negative film, would you have a color slide?

Yes, but it would be very low in contrast, if you copied a camera negative on a camera negative. It could be called "interpositive", and it should be masked to improve color reproduction because it wouldn't be meant to be viewed by eye at that stage.

"Print film" is the product you are after, Vericolor Slide Film was made until 2004 or thereabouts, it was process C-41 and was unmasked high-contrast print film for copying normal masked C-41 color neg films to make slides. Now, color motion picture print film is quite similar but for ECP-2 process and it may differ in contrast etc. a bit from the C-41 product.

Orange mask is simply compensated either in light source or in sensitivities of RGB emulsions in taking film, so all it does is improve color purity. But, the final piece of film, meant to be viewed by eye, cannot be masked for obvious reason (it'd look orange).

I'm not interested in actually doing it; my question was more about color theory and whether the colors would work out. Color theory is not yet intuitive to me; the concept of 'color negatives' seems pretty artificial to me.

Oh yes, it works out like this;

Original negative:
Red-sensitive layer creates increasing amount of cyan (minus red) dye -- more red in scene -> more cyan dye -> less red light going through the developed film. Similarly, no red in picture -> maximum amount of red going through the film because of no cyan dye.

Same logic goes to green-sensitive (magenta dye) and blue-sensitive (yellow dye).

This way, color negative is born.

Then, if you sandwich a developed negative with a new negative film and shine white light to it, thus creating a contact print or copy---

From maximum red (no red in original scene), you expose the red-sensitive layer most, creating much cyan dye, that absorbs any red light in the final piece of film. So, no red in original scene -> no red in final film. Thus, this is positive from color theory point of view. Again, same goes with green/magenta and blue/yellow.

Masking does not change anything in this theory --- it just adds some bias to exposures. Masking is done because of dye impurities that cause unwanted absorption in wrong wavelengths. You cannot remove this unwanted effect, but you can add extra absorption to other wavelengths (orange mask) so that the impurity is constant over the whole density range, and then, after orange mask AND impurities are summed up, they can be treated as a simple color cast and compensated with bluish (anti-orange) light to result in a very pure negative image. Or, usually, print materials are just made so that their sensitivity is higher for blue, compensating the mask automatically. This can be actually advantageous, because color separation in print materials may be done by separating the exposure levels enough and then layer order reversed and filter layer removed to simplify the product at the cost of photographic speed of red channel.

The three primary colours of light are red, green and blue. The negative of one of these colours is formed by the combined light of the other two.

Negative of red = blue + green = cyan
Negative of blue = red + green = yellow
Negative of green = red + blue = magenta

And it will work in reverse too so...

Negative of cyan = red.... etc.


Steve.

This might help you see what they are talking about. http://en.wikipedia.org/wiki/Color_wheel

hrst said:

Vericolor Slide Film was made until 2004 or thereabouts, it was process C-41 and was unmasked high-contrast print film for copying normal masked C-41 color neg films to make slides.

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I still have a couple of rolls of Velicolor slide in the freezer, and await the project when I need good slides from negs. The colour balancing would be worked out doing snipped exposures of a neg of a macbeth positive shot though a frame of mask of the film I am trying to dupe.

Doing this I should be able to calibrate the fitration reading the densities of the white to black 'grey' squares, much the same way I have worked out the needed balancing for using e-6 dupe film, and interneg film. Of the e-6 I have a few hundred feet, and a bit less than 100' of the interneg.

Vericolor slide film made superb slides that rivaled any Ektachrome or Fujichrome you may ever see. However, in my experience, the film kept rather poorly. I had 2 boxes on the shelf for about 1 year beyond expiration. One was opened, the other was not. Neither survived to make any suitable slides at that 1 year beyond expiration.

The film probably keeps well frozen.

Just remember that a negative of a negative is a positive. A positive of a positive is a positive and a negative of a positive is a negative. This applies to color and to B&W.

PE

That's well and good. The thing that's throwing me is that there doesn't seem to be any fundamental, physical reason why a color negative is the way it is. It's just engineered to work like that. I understand RGB color models ok; and CMY printing. But the structure and creation of the film itself, when I try to figure out WHY it's the way it is, comes down to "because they engineered it that way" and not because the materials work that way. In other words, a black and white negative is the way it is because that's how silver gelatin works. But the Red-sensitive layer of color film becomes more cyan with more red exposure because that's the what it was engineered to do. I'm not understanding the fundamental reason, if there is one, why we use negative film and negative paper; it seems to me that it could be engineered so that the red sensitive layer of the film becomes more red (a color positive, though not intended to be directly viewed, thus not low-latitude like slides), and the printing materials could be positive as well. I guess I don't know much about chemistry, but I don't think there is a physical reason why red light should cause something to turn cyan; it is all imposed by the RGB color model, and the engineering decision to use a negative/positive system.

I still need to try to use the Rollei Digibase to do this as it does not have the orange base.

BetterSense said:

That's well and good. The thing that's throwing me is that there doesn't seem to be any fundamental, physical reason why a color negative is the way it is. It's just engineered to work like that. I understand RGB color models ok; and CMY printing. But the structure and creation of the film itself, when I try to figure out WHY it's the way it is, comes down to "because they engineered it that way" and not because the materials work that way. In other words, a black and white negative is the way it is because that's how silver gelatin works. But the Red-sensitive layer of color film becomes more cyan with more red exposure because that's the what it was engineered to do. I'm not understanding the fundamental reason, if there is one, why we use negative film and negative paper; it seems to me that it could be engineered so that the red sensitive layer of the film becomes more red (a color positive, though not intended to be directly viewed, thus not low-latitude like slides), and the printing materials could be positive as well. I guess I don't know much about chemistry, but I don't think there is a physical reason why red light should cause something to turn cyan; it is all imposed by the RGB color model, and the engineering decision to use a negative/positive system.

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Just musing here...

I expect that the choice of complementary subtractive dyes (cyan for red, magenta for green and yellow for blue) is what permits the type of control you need when you turn around and shine a light through the negative for the purpose of making a natural colour positive print.

Otherwise I expect that it would be difficult to balance the effect of the dyes - you would get crossovers and have difficulties in accurately reproducing some of the colours.

Somehow I think we need a response here from a chemical engineer with a photographic processes speciality .

BetterSense said:

That's well and good. The thing that's throwing me is that there doesn't seem to be any fundamental, physical reason why a color negative is the way it is. It's just engineered to work like that. I understand RGB color models ok; and CMY printing. But the structure and creation of the film itself, when I try to figure out WHY it's the way it is, comes down to "because they engineered it that way" and not because the materials work that way. In other words, a black and white negative is the way it is because that's how silver gelatin works. But the Red-sensitive layer of color film becomes more cyan with more red exposure because that's the what it was engineered to do. I'm not understanding the fundamental reason, if there is one, why we use negative film and negative paper; it seems to me that it could be engineered so that the red sensitive layer of the film becomes more red (a color positive, though not intended to be directly viewed, thus not low-latitude like slides), and the printing materials could be positive as well. I guess I don't know much about chemistry, but I don't think there is a physical reason why red light should cause something to turn cyan; it is all imposed by the RGB color model, and the engineering decision to use a negative/positive system.

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You have a completely distorted vision of how B&W and Color neg work.

They are designed to give a print (film or paper). Working backwards, you get a long latitude color or B&W negative film. This allows over and under exposure which cannot be tolerated with reversal films. It also allows for excellent generational reproduction and color correction. The list goes on. This is all bound up in the theory of photo systems engineering.

PE

BetterSense said:

That's well and good. The thing that's throwing me is that there doesn't seem to be any fundamental, physical reason why a color negative is the way it is. It's just engineered to work like that.

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Well, the same applies to color neg than to bw neg; increasing exposure causes silver halides to reduce to Ag atoms which then work as a catalyst for developing reaction to create more Ag. Because Ag darkens film, and because more light->more Ag, the film is negative -- but same goes with color, dye is formed from oxidized developing agent amongside Ag, thus creating more darkening from more light. Now, what must be "engineered", is the selection of dyes. For red layer, we have to select a dye that is minus-red, etc. But well, actually this is a no-brainer.

The selection of primary colors, R G and B, however, is based on studies of human vision; our eyes do the same separation. That's why RGB works. Secondary colors are then just white - R, white - G and white - B.

But, I think that you have some misconceptions all the way. All films have very much engineering for them to work.

This color engineering, however, is based directly on how our eyes and brain work.

I guess I understand now. It's because color negatives were created on top of silver halide technology, which is inherently negative. So that the color part had to be engineered to be negative because the underlying silver halide technology is negative. I had forgot that bit. Although it would be possible in principle to have a film that had a negative density relationship but a positive color relationship, it wouldn't make a lot of sense to do that.

Since a given color layer works with silver halides, more exposure=less density in the final negative. You could use any dye couplers you want, but you have to use complementary colors for that particular layer because that's the obvious way to keep the neg/pos paradigm going.

BetterSense said:

I guess I understand now. It's because color negatives were created on top of silver halide technology, which is inherently negative. So that the color part had to be engineered to be negative because the underlying silver halide technology is negative. I had forgot that bit. Although it would be possible in principle to have a film that had a negative density relationship but a positive color relationship, it wouldn't make a lot of sense to do that.

Since a given color layer works with silver halides, more exposure=less density in the final negative. You could use any dye couplers you want, but you have to use complementary colors for that particular layer because that's the obvious way to keep the neg/pos paradigm going.

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Direct color positive systems exist. Dye bleach is one of them (Ilfochrome). You form a negative silver image and remove it along with dyes leaving a positive color image.

Polaroid color was also an example of this. You got a negative silver image which created a positive dye image.

PE

What I took from Better Sense's question was why were the particular negative dye choices made?

Theoretically one could have in the negative red mapping to green, green mapping to blue and then blue mapping to red.

Then, in the negative to positive step, just reverse the mapping.

In any imaging system relying on 3 color mapping and white light exposure using a single source and a single "image" of whatever polarity, the image dyes must map to Cyan, Magenta and Yellow. Absence of all 3 = white and presence of all 3 = black. The dyes cannot be R/G/B or any other miscellaneous hue. This defines the subtractive system.

A system relying on production of light as in TV phosphors, uses an additive system in which all 3 = white and none = black. This is just the opposite of the photographic systems.

So, arbitrary selection is really not an option.

PE