White Balance: Auto is better?

[Gregory]

I shoot RAW with a Mark III. White Balance can be set in the camera. I usually leave it at 'Sunlight' and make any changes necessary in Apple's Aperture. There are times though when the original colours are seemingly impossible to resurrect and I wonder if white balance is the problem (although insufficient light is also sometimes the culprit, even at 3200ASA).

I had assumed that the image information stored for each photo was identical regardless of the White Balance setting, and that the camera recorded the White Balance in a special 'field' within the RAW image. if that was the case, the White Balance setting could be left at Sunlight without any consequences.

I would however like to be certain. Does the White Balance setting change the image data? Is it better to set the White Balance to Auto or if you know what the white balance is, to that specific value? Or is leaving White Balance set to Sunlight and making changes in software perfectly acceptable?

regards,
Gregory

[Panopeeper]

The white balance setting, just like contrast, saturation, sharpness, color tone, does not affect the raw data; it is recorded in the raw file as meta data.

There is one difference between these settings, namely that WB will be honoured by all raw processors (even though not with the same result), while the other settings are ignored by most raw processors, except the "native" one, for example DPP.

However, all settings affect the in-camera display (image and histogram), the embedded thumbnail and the embedded JPEG image.

[walter.sk]

Does the White Balance setting change the image data? Is it better to set the White Balance to Auto or if you know what the white balance is, to that specific value? Or is leaving White Balance set to Sunlight and making changes in software perfectly acceptable?
Gregory
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I've found that in most cases the AWB on my 1DMkII is accurate enough so that I generally leave it at that setting.  Then, in ACR I compare the AS SHOT setting to ACR's AUTO WB if I'm not satisfied.

If the scene I am shooting has mixed light and/or is critical for me I do a custom WB on the scene, or put a little white card in the first shot and then use the eyedropper in ACR to click on the white card.

When I shoot panoramas I choose the most likely WB, e,g., Sunny, Shade, etc., in order to maintain consistent white balance over the several shots that comprise the pano.

[pcox]

As has been said, white balance in RAW mode is just an advisory tag that the converting software reads. No bits get changed in the image data.

I generally leave mine set to 'auto' and correct in the converter - auto does a pretty good job (on my 5D), so usually minimal tweaking is required.

However, if I had it set permanently to 'tungsten', it would make no difference, I'd just have to move the WB slider a bit further in conversion.

Peter

[pierisb]

As has been said, white balance in RAW mode is just an advisory tag that the converting software reads. No bits get changed in the image data.

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Is it known for certain that, under extreme WB conditions, the camera does not adjust per-channel analog gain, thus altering the raw data? Under tungsten light, for example, the blue channel is under-represented and could conceivably be amplified in the analog domain rather than in postprocessing, which would give you quantization noise.