Does white balance setting affect exposure when shooting RAW?
Asked 11/13/2012
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If you shoot RAW, the camera’s white balance setting is usually described as metadata that can be changed later without harming the raw file. But can the chosen white balance still affect the camera’s metering or exposure settings in auto/semi-auto modes? For example, if I always shoot RAW and leave white balance on Auto, Incandescent, or a fixed Kelvin value, then correct white balance in post, could that change the exposure the camera chooses or cause any loss of image information?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
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This is actually fairly easy to test, and so I did. I used my Pentax K-7, so this doesn't speak to all cameras, but I think at least many work the same way.
I worked in a dark room, lit only by an iPad app which simply turns the whole screen a certain color. I put the camera close enough to the screen that the color filled the entire frame, and, although I don't think it matters, manually focused. I put the camera in aperture priority mode with the lens at F/2.8 and ISO fixed at 1600. And I set capture to RAW.
With a red light and daylight white balance, the camera selected shutter speed 800. When I set white balance to tungsten (without changing anything else), it instead chose 640. I went back and forth several times to make sure nothing else was influencing the result.
Then I changed the light to blue. Here, with tungsten, the camera picked 1250, but with daylight, it chose 1000.
So, clearly the white balance selected does influence metering decisions made by the camera even in RAW mode.
However, it's also worth noting that even in this contrived, extreme case, the difference only one third of a stop in either case. Therefore, I think you're pretty safe with using Auto WB in RAW. (Which, by the way, happened to give the same exposure as Daylight in my tests.)
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
13y ago
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Generated from our catalog & community — verify before relying on it.
For RAW capture, white balance does not change the underlying raw sensor data, so you can correct it later without losing information. In that sense, leaving WB on Auto, Incandescent, or a fixed Kelvin setting does not directly “bake in” exposure changes to the raw file.
However, white balance can still matter indirectly on some cameras because it may influence metering, the JPEG preview, and the histogram. A community test found a camera choosing different shutter speeds under identical light when only WB was changed, so some cameras do let WB affect auto exposure decisions.
This mostly matters in edge cases: high dynamic range scenes, ETTR shooting, or situations where one color channel is close to clipping. In those cases, an inaccurate WB may make the histogram/preview less representative and can lead you—or the camera—to expose a bit differently.
Bottom line: RAW preserves the data, but WB can sometimes affect the exposure selected by the camera in auto/semi-auto modes. It usually won’t matter much, but in critical scenes watch the histogram and channel clipping rather than assuming WB is completely irrelevant.
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