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Why can I adjust the white balance of a RAW file but not a JPEG file?

I thought white balance adjustments were simple color-cast adjustments applied uniformly across the image? If this is the case, then why can I not accurately adjust the white balance in (for example) Aperture if the camera (SLR or iPhone in my case) has already made white balance adjustments?

Just to clarify, this I am referring to applying the white balance adjustment to the image as a JPEG. You cannot apply white balance adjustments to RAW files in the camera (at least not in any camera I know of).

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  • When you shoot in raw the camera has a white balance setting (auto, daylight, a custom temperature, a given benchmark picture). This setting is saved and you can access it by using e.g. the "As shot" setting in LightRoom. Then you can change it as you wish, to "fix" any glitch or to achieve your personal vision. With a jpg the wb is substantially set when shooting.
    – Francesco
    Sep 24, 2012 at 23:22
  • All Pentax DSLRs allow white balance setting for RAW when developing those RAWs to JPEG after the fact. Other brands I've used are similar. However, I'm not aware of any that let you alter in-camera the advisory metadata saved with a RAW file — kind of a minor feature but it would be nice.
    – mattdm
    Sep 24, 2012 at 23:34

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It depends if you are shooting jpg or raw. If you are shooting raw, the image that is shown on the LCD of the camera is just the jpg contained within the raw: but when you open it with a raw capable editor you still have room for setting the white balance. You still have to interpret the value of the raw data pixels and white balance is simply establishing what is to be interpreted as a 18% gray.

If you shoot with a jpg, this interpretation is made by the camera when you are shooting: you don't have the raw data any more but you have a finished image and you lose the latitude to decide what is gray.

DSLR always give you the chance to record your photo in raw format. By the way, often when you open the raw file, which is usually rather large, you see a flashy image, which disappears when the raw is loaded and is often replaced by a duller image. This is because the first image is the (already developed) thumbnail jpg within the raw, with a bit of processing already applied (saturation, contrast, whatever). The "dull" version is waiting for you to be processed.

On the contrary, the iPhone typically doesn't allow for raw shooting, so you are "stuck" with the jpg that it has produced. You can check this link for a possible approach.

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You are correct, white balance is just a global colour shift, and you can change it in post regardless of what the camera does. However editing a JPEG, which has already reduced to an 8 bit image, can be problematic as you get rounding errors when manipulating numerical values. This can reduce the number of distinct shades in your final image, which shows up as banding in areas with little texture.

This is why it is recommended to set white balance in camera when shooting JPEG as the calculations are done with higher precision values.

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Its not that the camera won't let you specify the White Balance in the camera when shooting raw, its that with RAW, the concept of white balance doesn't have (much? any?) meaning. Its expected that the post-processing program (Aperture, Lightroom, Photoshop, etc.) will control the white balance as part of the first steps of your post-processing.

Some post-processing programs completely ignore the RAW file's meta data that tells what the camera was set to (Lightroom 4). Others will read the meta data, and use it as a starting point (Aperture 3). But it really makes little difference, since the point of using RAW is to let you have complete control.

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