What Is a Histogram, and How Can I Use It to Improve My Photos?

 

What about a strange graph with all the peaks and valleys? Appears when you open Photoshop or edit a raw file on your camera. But what's that weird thing called a histogram, and what does that mean?

Histograms are one of the most important and powerful tools for digital image makers. And if you read a little, you'll see that some simple rules not only create a much more powerful image editor, but also take better pictures in the first place. What are you looking for? Read!

What Do I Need to Know About Histograms?

It may look scary, but the histogram isn't that complicated. They represent the distribution of tones throughout the image. This is a simple algebraic graph.
The horizon represents different values ​​in the image. The left edge represents pure black and dark shadows. On the right are your highlights and pure white. The value between the two drops as you would expect, with dark tones transitioning to midtones and then to bright highlights.
The vertical axis shows how much the corresponding value appears in the image, whether bright or dark. Higher peaks represent high concentrations of that particular value. In this example, the original image in this histogram has the highest density of the brightest highlights, and the slightly darker highlights show a sharp drop in density.
Digital images do not have unlimited tones. There are only 256 (8-bit information). In the histogram, black is 0 and white is 255. All dark tones have low values ​​and light tones have high values. It may look scary, but the histogram isn't that complicated. They represent the distribution of tones throughout the image. This is a simple algebraic graph.
The horizon represents different values ​​in the image. The left edge represents pure black and dark shadows. On the right are your highlights and pure white. The value between the two drops as you would expect, with dark tones transitioning to midtones and then to bright highlights.
The vertical axis shows how much the corresponding value appears in the image, whether bright or dark. Higher peaks represent high concentrations of that particular value. In this example, the original image in this histogram has the highest density of the brightest highlights, and the slightly darker highlights show a sharp drop in density.
Digital images do not have unlimited tones. There are only 256 (8-bit information). In the histogram, black is 0 and white is 255. All dark tones have low values ​​and light tones have high values.

Okay, But What Do I Use It For?

Histograms are great tools for photography because they allow you to do two key things. First of all, a histogram tool on a DSLR will allow you to see how balanced the composition you’re shooting is before you shoot it. Is it too heavy on the darks, or are the darks lost in the composition? Are the whites too bright—all the detail washed out of them? An in-camera histogram can give you a rough idea of how your image will take or has taken.
In addition to this, histograms can tell you what’s wrong with an image, as well. Sometimes, a potentially great shot gets exposed wrong, and you don’t have the time to bracket or recreate the moment. By looking at your photo’s histogram in an image editor after the fact, you can find out how to best bring your ruined exposures back from the brink, and get a decent, or possibly even a great image out what might have originally been a poor one.

Let’s take a minute to see a few of these badly exposed images, and how we can read a histogram to make them into better photographs. All of these images were shot in RAW by the author, and are processed and improved in Adobe Camera Raw. If you prefer not to use Adobe, there are usually free Raw Editing tools with DSLR cameras, as well as very good freeware programs like Raw Therapee . Adobe Lightroom is another program Adobe offers, this one a stand alone from Photoshop, often considered the new standard for Raw file editing and digital image developing.
For those of you shooting your images in JPG, and not Raw, you can definitely learn about histograms from this article, and pick up a few tips on how to improve your images, but you may learn more by learning how to adjust contrast like a pro specifically for non-Camera Raw files. All other readers, keep on going to pick up some simple tips on how to improve your photos.

The Shape Of Bad Histograms, and How to Improve Them

This shot is completely disappointing. Obviously, this was published to get the details of the sky, but the shadows of almost every image are ruined. Look at the histogram to see what needs to be changed to improve the image.

In this case, you can see that the largest spike is in the leftmost (darkest) area. These largest spikes represent most of the tones in the image. There are some spikes in the midtones to emphasize the range, but they are lighter in comparison.

Later some serious RAW file edits were made and our photos changed from unusable to pretty good. Let's see how the histogram changed.

Histograms aren't a perfect example of a textbook because of the distorted exposure, but they're pretty good for shots that fail completely. Only one image can be pushed so far. Anyway, at this point, there are no incredibly obvious problems with the image. It has a full tonal range from dark to light and has succeeded in preserving detail and color in most of the image. For reference, we have achieved most of this dramatic change by adjusting the "Auxiliary Light" slider to a dramatic and very high setting. Many tweaks have been made to the image, which was the key to bringing out the shadow details.

The second image, which was clearly exposed to grab the shadows, whitened the girl's skin, ruined the details of her highlights, and dropped all the dark details to near midtones. I did. Let's take a closer look at the histogram.

Wow. There is no darkness (on the left) and the highlights are concentrated (on the right). The image also looks almost flat. You need to add a better range of value and see if you can bring out the beauty of this photo.

By doing some work with the RAW file, you can bring out the full and rich darkness while preserving the highlight details. The shadows from her umbrella feel cooler, and the light from the sun still creates great highlights on her pale skin. The only difference is that she isn't shining.

The first good step in a Camera Raw file that is overexposed and lacks highlight details is to adjust the exposure slider first. In this example, we first stopped the whole thing (enter –1.0 in the exposure box). This will start shifting the entire range of values ​​towards the darker edge of the histogram (to the left). From there, adjust the contrast (I've removed a lot of it here) and add a lot of black to the image to bring out the darker colors from the hair without losing all the details.
In this case, we are focusing the tone in the dark areas for a reason. These darkness pops really white highlights and creates a great focus along the face and neck. There is plenty of room for personal choice and clever decisions.

Taking a Good Exposure One Step Further

You may not have a complete histogram of the great range of bright, dark, and halftones, but this image is reasonably exposed. But at a glance, even if the image is more or less okay, you can improve the harsh quality of shadows and add details very easily.

Adding a half-stop to your exposure improves underexposed shadows, adds great highlights to your skin, and gives you a bright sunlight look. You can adjust the Black slider to move the shadow to a point that barely touches black on the left side of the histogram, while preserving the details of all the different shadow areas. By making some artistic changes to "contrast" and "clarity", our image is already improved over a rational and decent image.