The 40D can show either a Brightness histogram or set of three separate Red, Green, and Blue histograms in the full information display during picture review. Brightness histograms give you information about the overall tonal values present in the image. The RGB histograms can show more advanced users valuable data about specific channels that might be “clipped” (details are lost in the shadows or highlights). Select Histogram from the Playback 2 menu and choose Brightness or RGB. You can read more about using histograms in Chapter 4.