NegaFix Exposure slider

[newedb]

I use the SE Plus version comes with my Plustek 7500i to scan Kodak Portra 160VC and other negative films, and observed this.

As I understand, the slider can change exposure in +-3 f stops range. But when I use it, it does increase the overall brightness of the picture when it slides to the right; but it does not change the brightness when slid even to -3, what's more interesting is that it actually changes the color balance, and makes the picture less red.

Is that normal?

[LSI_Morales]

Dear newedb

There are certain film emulsions which curve difference between the underexposed and normal exposure are minimal (but they are not identical), this is completely dependent on the film emulsion.
You should also consider that some artifacts in the emulsion can cause the threshold not to work properly, in such cases you should adjust the auto value slider to the right, this might help correcting such problems.

Cheers

[newedb]

I am sorry if I did not describe my problem clearly.

The problem I have is this, I have a slightly overexposed picture, and want to reduce exposure a little bit. But when I move the exposure slider to the left, the picture does not appear darker, instead, red color becomes weaker, green color becomes stronger.

[LSI_Morales]

Dear newedb,

I understood you perfectly. I believe it was me who did not make myself clear.

To create the three curves for every NegaFix profile, we use special targets created with the purpose of calibrating photographic labs, these targets are created under controlled conditions to reflect the maximum range of every emulsion.
Some emulsions do not have a big difference between the correct exposure and the underexposure limits whereas the difference might be bigger between the overexposed and correctly exposed shots. And this is also dependent on the answer from the scanner to every specific emulsion.

That is the reason why some NegaFix profiles will not present a considerable difference between normal exposure and underexposure (this is a seldom effect present in very few profiles).

Sometimes underexposed pictures have some cracks or artifacts, which are not easily seen by the naked eye. These small artifacts affect the histogram creating some color cast, for that reason you should use the Auto-threshold slider.

Cheers