Lightroom: RGB Curves

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  • Idea
  • Updated 8 years ago
  • Implemented
  • (Edited)
I have no idea what kind of impact this has on Lr's dev editor design, but many of us would like this built into Lightroom if possible.
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Rob Cole

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Posted 9 years ago

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John R. Ellis, Champion

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Here's a narrow use-case for allowing RGB curves/levels of slide scans to be adjusted separately. I fully recognize that it's not squarely within LR's sweet spot of digital camera images, though based on these forums, there are "many" people using LR to manage scanning:

I scan large numbers of Kodachrome slides that are 30-60 years old, using a Nikon LS-5000 scanner and Silverfast calibrated to a Kodachrome target. Using visual comparison, the scans seem very faithful. Both the original slides and the scans tend to have a modest red cast that can muddy the shadows, especially if I then adjust the tonal range of the shadows, e.g. by increasing Fill Light. This cast is readily apparent if you look at the LR and Photoshop Elements histograms:

The fastest, most reliable way to correct this is to move the black point of the red channel. Sometimes the LR White Balance Selector (eye dropper) can address this, but it's fussy and unreliable and I can end up in a pixel hunt for neutral tones. So I end up opening the scans first in PSE to adjust the red channel, then doing most of the processing in LR, and occasionally going back to PSE if there is dust, scratches, or fungal splotches that can't be fixed with LR's convenient but limited Spot Removal tool.

I don't know where this red cast comes from (inherent in the film or original processing or aging), but it's clearly visible on a large fraction of the originals.