Yes, i was also thinking about adding a button to re-calculate multipliers. I wouldn’t add a dedicated ROI selection tool, instead i would just add a single button labeled “Re-calc multipliers from current crop”; this would be based on the usual crop tool, but would alter the multipliers only when intentionally clicked.
Anyway, i would also like to revise the whole “auto-gain” concept, because i think it has some flaws. For example, let’s say you’re walking down the road and you shoot two pictures, a few minutes apart, both in the same lighting condition. In the first one, the frame is dominated by a big green tree. The second one is dominated by a big red wall. Everything else (the road, the sky, etc.) is the same.
Ideally, you would process these 2 pictures with exactly the same WB values, since lighting is the same. With the current auto-gain feature, instead, in addition to being skewed by the empty film holder area (as @matt_jones discovered), the channel gain is also skewed by the image content. After setting the perfect WB values on the first picture, if you then copy/paste the processing profile on the second one, you’ll find that you have to re-balance it, yielding different WB values than before. This is not a major issue (you can quickly spot-wb on the grey paved road), but i find it a bit annoying, especially if you have to process many negatives and you want to “industrialize” the process as much as possible.
So, i was thinking about saving the multipliers in the .pp3. This could be a working solution:
- when you enable the film negative tool for the first time on a picture, and the multiplers are not set, they are calculated automatically and saved to the pp3
- if the image is too dark, or you’re not happy with these multipliers, you set the desired crop, and hit the “Re-calc multipliers from current crop” button. The new multiplers are saved to the pp3. Now you can even select a different crop area, multiplers won’t change.
- now you fine-tune Exposure and WB to taste; when done, you can copy/paste the processing profile on the entire roll, and all pictures with the same lighting will have consistent color balance, regardless of the content.
I’ll try to experiment a bit… opinions appreciated!