Understanding the Histogram

One of the most useful yet most ignored camera features is the histogram. The histogram is available in most, if not all, digital cameras. It can be viewed in the LCD while you are also composing your shot, or separately after the image is taken.

What does a histogram do, exactly? Simply put, it measures the brightness of a scene.  You will see a graph with a strip below it showing black at the left and white at the right, with all the gradients of gray in between. This includes all the pixels in your image.  Now the graph counts the number or pixels at each level between the black and white areas in an image. The deepest darkest shadows are to the left of the graph and the bright highlights are found at the right. The heights of points in the graph shows how many pixels are found at a certain brightness level.

If your image is underexposed and is very dark, most of the pixels will be situated at the left side of the histogram, probably even hitting the left edge. If the scene is too bright, majority of the pixels will be at the right side. This histogram shows most of the pixels in the middle area, which means the scene or image is more or less evenly exposed. An evenly spread pixel area doesn’t mean your image is now perfect, just that the exposure is balanced. The histogram of a dark key image might show most of the pixels at the left of the graph but that’s okay because you intentionally are making the image dark.

Although the best judge of the exposure of a scene is still our eyes, the histogram can greatly aid us when it is hard to see the image in the LCD such as when we are out in the sunlight. With this graph, we can also foresee whether the scene will come out too dark or too bright and we can adjust our camera settings accordingly. 

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