Where to find your histogram
The regular white and black histogram shows the spread of tones or brightness levels in the picture. First, press the playback button to display an image, and then cycle through the playback displays (on Canon DSLRs, press the DISP button; on Nikon DSLRs, press the up and down arrows on the multi-selector).
Live view histogram
The same brightness histogram can be called up during Live View shooting (if your camera has this feature). The difference here is that it’s a live histogram – as you move the camera around or alter the exposure settings, the histogram will change shape to reflect the changing brightness levels.
If either of these histograms show over- or under-exposure, use your camera’s Exposure Compensation feature to make the shot darker or brighter before you take the next picture. Press the +/- button on the back of your camera and turn the control dial to do this.