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The histogram is one of the Photographer most important tools, and is under used by many Photographers. All DSLR and most digital point and shoot cameras have the ability to display both the image and Histogram on the camera’s LCD screen.

After each shot, I will examine the histogram to discover whether the image contains a good range of tonal values. The brightness levels for every pixel in the image are recorded, for a 8 bit this level can range from 0 to 255. (0 is absolute black and 255 is absolute white) The horizontal axis of the histogram represents the brightness level and thus has values of 0 to 255. The vertical axis of the histogram represents the number of pixels that have one particular value.

The image and it’s histogram below displays a good range of tones. You can see that the majority of the pixels are close to the center of the histogram.

A light meter, records for mid tones which has a numeric value of 128, the reading will be an average of all the areas of the image that camera considers important. (How theses areas are determined are dependent on the meter setting that you have selected, i.e. spot, center weighed etc). If there are more dark or light areas in the image the camera may under or over expose these areas respectively. This means that a dark image will have many pixels with brightness levels that are close to 0 and that a light image will have many pixels with brightness levels that are close to 255. The edges (about 5 pixels) should not be taken into consideration when you are analyzing the image. As these are at the edge of the sensor dynamic range. The distribution of the pixels is a complex subject which has been simplified for clarity.