Banding/local colour casts on negative scans

I am scanning old negatives with my Coolscan V ED. On many of the negatives, I am getting banding or patches of (most often yellowish) discoloration. I suspect this is a result of the negatives having been stored under too warm conditions. An example of the discoloration can be seen in the attached image - it is a yellow band going across from left to right, on top of the tree and sky.

I am looking for any tips/hints from people about methods I could use in post-processing to reduce or remove these colour casts. I have experimented with some techniques in darktable but not found one that works well. Happy to take example techniques from folks for other software as well, I am sure I can adapt them to darktable also.

That is a color hue. They are more easily seen in light colors like that bright sky if the hue is not heavy.

To remove the yellow, just simply use the "Hue and Saturation" slider in Photoshop, or there might be a correction slider in your NikonScan software

Honestly though, the image doesn't look that bad

Reminds me of when I used to live near Los Angeles, and before the stricter automobile emission standards,

there was usually a brown cloud over most of Los Angeles. Some times of the day, you can taste the air.

But if this isn't near a major city, then maybe it isn't a smog cloud over the city.

There is some coloring that comes to black and white negative that haven't been fixed and

washed as well as they should be, after aging or poor storage conditions. I suppose those could

happen to color images, too.

Reminds me of when I used to live near Los Angeles, and before the stricter automobile emission standards,

there was usually a brown cloud over most of Los Angeles. Some times of the day, you can taste the air.

:)

OK, so this is not smog. To demonstrate this more clearly, I have attached a new image where you clearly see the 3-4 vertical bands across the image.

That is a color hue. They are more easily seen in light colors like that bright sky if the hue is not heavy.

 

To remove the yellow, just simply use the "Hue and Saturation" slider in Photoshop, or there might be a correction slider in your NikonScan software

How would you suggest I apply the hue adjustment? I'd have to paint a mask using brushes, I assume - if I just apply the adjustment uniformly to the whole image it will not deal with the issue, and will impact the rest of the image in an unwanted way.

How would you suggest I apply the hue adjustment? I'd have to paint a mask using brushes, I assume - if I just apply the adjustment uniformly to the whole image it will not deal with the issue, and will impact the rest of the image in an unwanted way.

In your first image the banding wasn't noticeable. In the second image, yes it is noticeable and my guess it's because the negs are old and have "yellowed" over time. I have similar yellowed negs but they have "blotched" areas rather than bands. No, a uniform adjustment won't fix them, so I'm not sure what you could do. Other members might know.

Looking at the second picture, and specifically how we as humans look at it, we see a

correlation of yellowness in vertical bands. This is most visible in the sky.

I suspect that if you just take the upper (sky) part, then integrate on the Y axis,

(resulting in a function of x), and then low-pass filter the result, that you can get

close to the distribution of the yellowness. Then subtract that distribution.

I don't know if any common editing programs do that operation.

The highly exaggerated saturation won't help. Any slight colour variation is going to be made much more obvious by pushing the saturation slider too far to the right.

Apart from using a more realistic saturation level, I'd tackle this by creating a duplicate layer that has the yellow corrected in the deepest part. Then with the original image as a top layer, rub through with a low opacity (~ 5%), soft-edged eraser brush to locally reveal the corrected layer.