What Is It?
Looking at the Histogram on your camera can help you improve the overall exposure of your images and it’s a tool that’s available on most models. It’s a graph that represents the range of tones that are in the image you’ve taken so you can analyse the shot to make sure the exposure is correct before you move on to take a photo of something else. The left side of the graph shows the darker tones and the right the lightest.
You can set your camera to show a histogram at the same time you preview your shots, see your camera’s manual for more information on how to do this.
Why Should I Use It?
Even though the histogram looks at the tonal range of your shot, it’s a quick way for you to see if your shot is really over or underexposed. If your shot’s underexposed it will look too dark while an overexposed will look a lot brighter than it needs to be and really light areas can look blown out as they lack detail.
What Does It Mean?
If the graph is occupying mostly the left-hand side it means your image has more dark tones than light (underexposed) and if it’s shifted to the right, there are more lighter tones (overexposed) which means you could have really bright areas that look blown out.
A 'good' histogram that shows an even exposure will peak more towards the middle and get lower to either end.
Also, as a side note, when you playback your images there’s an option you can set that makes the highlighted areas ‘blink’ so you can pinpoint their exact location. Check your camera’s manual for the instructions on how to do this.
When To Use It?
How often you check your histogram is up to you but generally, cameras are quite good at setting the exposure for most scenes. However, there are a few scenarios that can confuse your camera and these are the times it’s worth checking the histogram. For example, if you have a scene that varies drastically in tones so you have really bright areas as well as dark shadows.
The same goes for times when you’re using the same settings for a series of shots that you want the exposure to be the same for each. This could be taking a series of portraits that you’re going to combine into a multi-portrait that shows one person in several different locations in your shot. If the exposure isn’t the same in all the shots they won’t blend together seamlessly and it either won’t work or it’ll mean you have more post-production work to do.
There are times when the readings on the histogram would be right, your shot isn’t correctly exposed, however you may have done this on purpose so it can be ignored. When is this true? Well shooting a silhouette would give you a histogram that isn’t considered ‘correct’ likewise for a shot where the ground and sky are of a similar tonal range such as one a beach or when it snows.
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