All cameras are capable of displaying a histogram on the back LCD, and should rather be used as opposed to using the picture displayed on the back LCD. The Histogram displays the tonal range of the image, and will indicate if you have under or over exposed an image,
On the left hand side of the histogram are all the shadows (blacks) indicated by the value 0, and to the far right are the highlights indicated by the value 255. In the middle is pure grey with a value of 135. One should always aim to have the centre peak of the histogram slightly right of middle (called shooting to the right) , as 2/3 ‘s of the image detail sits to the right hand side of the histogram and all the noise to the left hand side of the histogram. Ideally one should overexpose between 1/3rd to 2/3rds to create the ideal histogram.