Why Do We Need Photography Histograms
The histogram is a useful but often misunderstood tool that your camera provides to help you get the correct exposure on your images.
What is a histogram:
A histogram is a graphical representation of the pixels exposed in your image.
The left side of the graph represents the blacks or shadows, the right side represents the highlights or bright areas and the middle section is mid-tones (middle or 18% grey). How high the peaks reach represents the number of pixels in particular tone. Each tone from black to white is one pixel wide on the graph, so imagine the histogram as a bar graph all squished together with no spaces between each bar.
How to adjust your histogram:
When your graph is shifted too far in one direction or the other so that it does not even touch the other edge – that means you can safely shift your exposure to cover more of the range of tones. Here are some examples:
This graph shows an overexposed image, notice the gap on the left side indicating a lack of any blacks represented. It also means you will lose lots of detail in the white areas that may not be recoverable. In this case shift to give your image less exposure and shoot the scene again.
This one shows the opposite. Now we see a gap on the right side of the graph indicating there are no whites represented so the image will be dark, too dark. You can safely give the image more exposure until you see the graph just touch the right edge of the graph.
Importance of Histogram
The histogram is not necessarily good for evaluating your exposure but the “correctness” of it depends on too many factors, not the last of which is your vision as well as the scene you are photographing. Histogram merely shows you the amount of tones of various brightness levels in your image, and nothing more. It can be used to discover whether you have clipped any highlight or shadow detail at specific exposure settings. You can use it as a guide to avoid such loss of detail as you take pictures, and that is where histogram excels. As long as you keep that in mind, in general, there is no “good” or “bad” histogram.
