Luminance histogram and RGB histograms in digital camera

One of the nice features in digital camera that cannot be found in traditional camera is the ability to display histogram.

Histogram shows the distribution of brightness in an image horizontally, and the amount of brightness vertically. A typical histogram looks like mountain as below. It is a handy tool to evaluate the exposure.

If you see the peaks are gathered on the left, the image is dark; and if you see the peaks are gathered on the right, the image is bright.

In normal situation, we would like the peaks to be in the middle, so that there is no under-exposure (too dark) or over-exposure (too bright). However, there are situations when dark is OK (e.g. shooting the Earth Hour scene) and there are situations when bright is OK too. Anyhow, you can make use of histogram to assist you in adjusting the exposure value of your picture.

Canon PowerShot S95 camera is able to show histogram in Shooting Modes and Playbank Modes. Histogram is not available in Auto modes (you won't need it, as the camera is taking care of the exposure adjustment for you), and is available for P, Tv, Av, M modes.

Canon PowerShot S95 has two customizable shooting displays, and the default setting for each of the shooting modes is different. You can use the Custom Display setting to turn histogram on or off for either one or both of the shooting displays. You can switch between the custom displays using the DISP. button.

Histogram can also be shown in Playback screen of Canon PowerShot S95. You need to switch to the Detailed Information Display playback screen in order to see the histogram of the picture. You can rotate among the available playback screens by pressing the DISP. button. You can set the default playback mode with the Review Info option.
Canon PowerShot S95 is able to display the RGB histograms of the picture in Detailed Information Display screen. You can toggle RGB histograms on and off by pressing the "Up" button when you are in Detailed Information Display.

The RGB histograms show individual graph for each of the Red, Green and Blue colour captured by the camera in the picture. This will be good piece of information to judge the colour and white balance of the picture.