RGB Histogram

[jodaco]

I recently upgraded from a 20D to a 50D (very influenced by your info Bob - Thanks!). One of the things that I looked forward to was the RGB histogram. On the 20D I always used the histogram to verify exposure but was often frustrated when a channel (usually red) would clip even though the luminance histogram showed as much as a third stop of space. I was fiddling with custom white balance on the 50D and noticed that when set to Cloudy the red channel would clip although the luminance was fine. This is fine since that's what having the RGB is for. But then I set the custom white balance with a BALens and shot the same thing again. Then all the channels were essentially the same and matched the luminance histogram. I realized that even though I am shooting RAW what I am seeing in the histogram is based on the jpeg preview. So how do I know in camera if I am really clipping a channel in the RAW data? Is the custom white balance the best setting? Is there a way to get a "flat" unaltered reading in the histogram?

Thanks in advance.
-Josh

[Bob Atkins]

As far as I know, the RGB histogram is always based on the JPEG image, even if you are shooting in RAW mode. I don't think there is any way to view the true RAW histogram on the camera. Certainly if you don't clip the JPEG you won't be clipping the RAW data and that's probably something to aim for.

I suppose using the camera with everything set to default or even to their miniumum setting(sharpness, contrast, stauration etc.) would produce a JPEG histogram that held onto the most amount of information from the RAW file.