A few weeks ago, I explained how to use the histogram to get a better exposure. And although the default histogram will give you a general idea of an image’s exposure, there’s actually a special histogram that’ll tell you a lot more: the RGB histogram.
Here’s how it works:
If you understand the regular histogram, then the RGB histogram is simple: it shows you the histogram of each individual color channel (red, green, and blue).
The bad thing about the regular histogram is that it lumps all these color channels together, making it hard for you to see if you’re underexposing or overexposing a specific color channel. And, on some cameras, I’ve heard that the regular histogram only shows you the green channel.
So, the RGB histogram is similar to the regular histogram, but now you have a separate histogram for each color channel.
The goal is the same: you don’t want to underexpose or overexpose any of the color channels, so look at each channel’s histogram to ensure the graph isn’t bunching up to one side.
It’s important to note that each color channel’s histogram may be drastically different. It really depends on the colors of the photo (and their brilliance). For example, consider the photo below of a Desert Five-Spot (my favorite desert wildflower, btw):
Here are the corresponding RGB histograms of this image:
Notice how the green channel doesn’t spread all the way to the right? At first, you might think this means the image is underexposed, but remember: this is only the histogram of the green channel.
With the RGB histogram, your goal is not necessarily to get a balanced histogram in each channel, but instead to ensure you’re not losing details in a color channel by underexposing or overexposing.
So, although the green channel doesn’t have many highlights in this image, notice how the blue channel does: its histogram is spread out and nearly touches the right side. The important highlights in this image are in the blue channel, so that’s what I exposed for.
How to enable the RGB histogram on your camera
Although most cameras have the standard histogram, not all have the special RGB one, so you may be out of luck, but check or camera’s manual to make sure and don’t be afraid to do some digging in your camera’s menus or custom functions since it’s not the default setting.
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About the Author: Steve Berardi is a naturalist, photographer, computer scientist, and founder of PhotoNaturalist. You can usually find him hiking in the San Gabriel Mountains or the Mojave Desert, both located in the beautiful state of California.