Green Fog in Color Negative Scan

Question

Can anyone explain what is wrong with this negative scan?

There seems to be some green haze in my scans. At first I thought the green tint was just from the lab not color correcting the scans properly, but it's more than just a color tint, there's some real fogging too.

The film is Cinestill 50D, this is my first time playing with this stuff.

Some example scans:

And a photograph of the negative on the light table:

Hypothesis:

• Green tint is from poor scan job but the fog is because negatives were underexposed.

All my other films done with the same camera and meter are correctly exposed, why would this one be any different? Plus, the negative itself looks dense. If anything, it's overexposed for the second shot.

• Green fog comes from light leaks in the camera.

All my other films done with the same camera don't have this problem.

• Green fog comes from carry-on x-ray at the airport.

This film is an ISO 50 film, so this seems unlikely, however maybe the cine emulsion is more sensitive to x-rays compared to normal photography emulsions?

• Green fog comes from poor scan job itself.

I looked at the negative under the light table, honestly, I can't tell.

So, what is it?

Answer 1

There is nothing wrong with those negatives:

So, where is that green fog coming from?

Here's an explanation: As you clearly shown on the third image film negative has an orange layer. (For an explanation of why that is read this link)

If you scan the negative and just invert the colors you are inverting that orange layer as well, and that will give the image that greeish fog.

Most folks would want to color correct and add magenta or do other kinds of distortions to the color of the image, but the key concept is that the orange layer is not part of the picture

In for a longer explanation:

On a negative you would expect the white areas of the image to be recorded as black, and therefore and the black areas should be white.

The orange layer is the unexposed part of the film, no light information has been recorded on it. It is the considered the minimum density of the negative. When turned into positive it should represent the darkest possible value: black.

So... shouldn't the area with the orange be white instead of orange?

It is that simple: that orange information has to be converted into white before we invert the picture, and to do that the information for the orange layer has to be discarded or at least turned into a neutral value that represents the brightest possible point in the image.

Using the curve tool (it can be also done with the levels tool too) find where the pixels for the orange layer are on the histogram, and move the max value of the curve to clip the information so that the max values are white.

Really? discard that much? Yes, is not part of the picture, it should be white or a very very very bright neutral color, so that when it is inverted it represents black.

Once you got rid of that extra information, invert the picture. Your black levels should be correct and neutral and the ratios between the colors should be ready to do proper color balancing.

Note that because of the relative low density of negative film and because you will be throwing away a lot of information, and stretching the curves (or levels) significantly, it only makes sense to digitize using a high bit depth of 16 bit per channel or better (AKA 48 bits per pixel or better)

The best place to find the values for the orange mask are in the edges of the pictures, but a segment of unexposed film can save you a lot of guessing.

When digitizing a full roll of film is surprisingly easy to get consistent results. Once you found the values for the orange layer, you can pretty much use that setting for the whole roll and it should work (For that I recommend scanning or digitizing with a fixed exposure and avoiding any kind of auto-color auto-exposure or auto-anything)

Answer 2

Some things to try to troubleshoot the problem…

The colour of the film base, if not corrected accurately, could shift the colour of the scans in a consistent way toward green for all the shots on the roll regardless of the density of individual images. The exposure looks useable to me.

Look closely at the edge numbering of the film. The exposure of that information is usually stable. Use it as some indication of the processing that the film received.

Any light leaks in the camera would begin to be evident in the clear area between the frames and along the edge of the strip. Compare the clear areas at the tail of the strip with them. Remember that the tail of the film never left the cassette and wouldn't have been exposed (!) to any light leak. The tail of the film was processed directly from the factory. The head of the film, on the other hand, was in the camera for the whole duration until it was rewound into the cassette prior to processing.

Lastly, compare the tail of this film stock side-by-side with another colour negative film base that has been successfully used. Is there any difference in colour or density of the film base?

Answer 3

Green tint is from poor scan job but the fog is because negatives were underexposed.

The picture of the film on the light table does not look underexposed. Except perhaps one frame.

Green fog comes from light leaks in the camera. All my other films done with the same camera don't have this problem.

Light leaks usually aren't uniform across the frame.

Green fog comes from carry-on x-ray at the airport. This film is an ISO 50 film, so this seems unlikely, however maybe the cine emulsion is more sensitive to x-rays compared to normal photography emulsions?

I can't provide any opinion based on my own experience, but my guess is no.

Green fog comes from poor scan job itself.

Most likely. I did not use cine films for at least two decades, but I don't think they changed too much. These films are usually less saturated and less contrasty than regular still photography negatives, especially if developed in the cine processing chemistry (intended for this kind of films). And if developed in C41 (standard still photography process, likely modified to remove the Remjet layer) some color issues might have been introduced. These films also usually have different color of the orange mask. So I don't think it is surprising that the film does not scan well on system that is configured to scan standard still photography negatives.

Another thing - what is the source of the film? These things are usually cut from leftovers after filming. How old is the film, isn't it possible that it is pretty old or not well stored?

Update: I tried some curve edits on one of your images and it looks like it can be brought to a reasonable state with some effort. That makes me think that (lack of) correction while scanning or after is the problem here.