Originally posted by Delgado RAW shooters should also keep in mind that the histogram is based on the embedded jpeg in any RAW file, and is not an entirely accurate representation of the way that a RAW file will deliver an image. Often when a histogram shows blown highlights, the RAW file will still deliver a good image. If you shoot RAW, the histogram needs to be interpreted less literally.
I need to make a correction to my previous post. Depending on memory is always a mistake.
The K5's histogram represents what would be produced if you were shooting in jpeg at the existing camera settings. Jeff Schewe and Bruce Fraser's work on Camera Raw comments that camera vendors tend to apply a strong tone curve to the default Raw to jpeg conversion (possibly in an effort to mimic the appearance of transparency film). The on-camera histogram is useful as a rough exposure guide, but not much else. Overexposure warnings (say where the histogram shows clipping to the right) appear to be quite conservative. Raw shooting will give more scope than the on-camera histogram suggests. For an accurate histogram, you will need to view your files in post-production - in for example, Camera RAW or Lightroom.