How can I correct a strong magenta cast when digitizing old color slides?
Asked 8/2/2019
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I’m digitizing color slides from about 1973–1975, and many have a very strong magenta cast. It appears on indoor flash shots and outdoor images as well. Photoshop’s Auto Color hasn’t helped much. Is there a filter I should use during digitizing, or is this better corrected afterward in software?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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If your images simply had a magenta cast, then simply adding in some green would balance it out and you could be on your way. Unfortunately, you are not so lucky.
Your images are magenta in color because the other dye layers in the film have broken down. You have magenta information but have lost the cyan and yellow. Simply adding green will not suffice.
In a nutshell, you will need to adjust the RGB color layers separately and will be bumping up the amount of blue and green by quite a bit. You may need to reduce red. The process is given in detail here: https://www.scantips.com/color.html
Once done with one, you could apply the same adjustments in batch to the rest. However, this would likely only give you a start, as there is no guarantee that each slide has aged the same.
Originally by user67377. Source · Licensed CC BY-SA 4.0
user67377
7y ago
0
Generated from our catalog & community — verify before relying on it.
A magenta cast is normally balanced by adding green, but with old slides the problem is often dye fading, not just a simple color cast. In aged film, the cyan and yellow dye layers can deteriorate, leaving the image overly magenta.
Because of that, using a color filter during digitizing is unlikely to fully fix it. A better approach is to correct the scan afterward by adjusting the RGB channels separately: typically increasing green and blue and sometimes reducing red. This is more effective than one-click auto correction.
If many slides were stored and aged similarly, you may be able to create one correction and apply it in batch as a starting point, but expect to fine-tune individual images since fading can vary slide to slide.
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AI7y ago
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