Some people may wonder, “What is that weird looking graph that you see pop up in your camera display or in editing software?” That graph is called the histogram and as a photographer it can be one of your best friends. To explain the histogram in it’s simplest form, it is a the graphic display of all the tones in a photograph. It shows the levels of brightness, as well as the color tones from red, blue, and green.
Above is how the basic histogram looks. The levels of black are on the left and the levels of white are on the right, leaving all the midtones in the middle. The more of darks, midtones, or lights in the image, the fuller the graph will be in the represented portion. This may look and sound like a bunch of nonsense, but I’ll do my best to show some examples and it will hopefully click for you.
Now judging by the histogram in the image above you can tell it’s loaded with dark values. The dark, night sky and shadows take up a majority of the scene so in the histogram you can see that’s where the bulk of the graphic lies. The little bits of brightness appear as specs towards the whites (right side) of the histogram. It can also show you if any of your blacks or whites are being clipped, meaning pushed beyond the sensor’s range, losing all detail, and going pure black or pure white.
On the opposite end, this photo is almost all light values. It contains almost no mid tones and blacks so the levels sit on the right side of the histogram. The small spike in the dark (left) end of the histogram is the high contrasting horses that are dark in the scene adding the small amount to the dark end.
Now, what’s the point in learning this? Today’s modern digital cameras have fantastic in camera metering systems to ensure that you get proper exposures, so what’s the point? Well sometimes you either can’t trust your camera’s meter or you want to alter your camera’s exposure. Most people when shooting rely on the LCD screen to view what their image is going to look like, however this can be very misleading. When you are out in the field shooting, you often will be in a variety of lighting conditions and that will effect how your LCD looks to your eye. Think about your cell phone- when you are indoors in dim lighting or at night, you turn your brightness down otherwise it looks ridiculously bright and hurts your eyes to look at. Now think of when you walk outside in the bright sunlight, you turn your brightness up all way and the screen still looks dark and hard to see. With that in mind, imagine shooting out in bright day or on a snowy field in the sun and relying on your LCD for your image to look proper- you will more than likely think your photos are underexposed since they look so dim and dark on the LCD and want to compensate for that by increasing your exposure to make them look brighter. Then when you get back inside or load the photos, you see they are all blown out and overexposed. The same goes for shooting in dark conditions, just the opposite.
This is where your histogram can come in handy. By seeing a visual representation of the tones you can learn to judge how the histogram should look by looking at what tones are in the scene with your eye. Like the first two examples I gave you, a bright scene on your histogram may get underexposed by your cameras meter or overexposed if you go off your LCD output. However if you use your histogram you can look and see that the values are where they need to be and make sure none of the highlights or darks are clipped. In my opinion this is an invaluable tool when shooting out in the field that every photographer should get comfortable with using.
Below are a few more example photos with the histogram alongside.
A good practice is to view your own images in editing software and pay attention to the histogram in order to train your eye. Now when you go out and shoot, keep your histogram on your LCD screen and you can view it while out shooting to ensure you always keep your images exposed just how you want! I hope this article helps you get a better understanding of what the histogram is and how to use it to advance your own photography.