There are a lot of tools to help a photographer take better photographs. One tool that can give a fast and dirty indication of a picture’s quality is the photography histogram. Using the histogram feature of your camera can help you decide if a shot is a keeper or should be redone.
What Is a Photography Histogram
In photography the histogram is a tool that shows the photographer how light is distributed across the photograph, from the shadows to the highlights.
That difference is known as the dynamic range. A scene that has very bright highlights and very dark shadows may force a choice: lose all detail in the shadows, highlights, or both.
Do not confuse dynamic range with exposure. Exposure is how much light reaches the camera sensor or film. Dynamic range is the difference between the darkest point on the image and the brightest. Which brings us back to the question, “What is a histogram?"
A histogram is a graph showing the brightness of a photo, from the darkest areas (the left side of the histogram) to the brightest (the right side). If the graph is higher on the left, more of the image is dark. If it is higher on the right, more of the image is bright. If it is fairly even across the graph the image is balanced between light and dark.
How to Read a Histogram
Reading a histogram isn't hard, once you understand what it is telling you. One of the many ways of looking at a potential photo is to consider the brightness of the image. Brightness is divided into three levels:
- Dark areas, or shadows
- In between areas, or midtones
- Bright areas, or highlights
The histogram measures brightness in 256 steps, ranged from 0 (darkest) to 255 (lightest). That is the horizontal, or x-axis. The vertical, or y-axis, displays how many pixels are in each of the 256 steps.
Usually a good histogram will be a little like a bell curve, with the high point somewhere toward the middle and the left and right sides much lower. If the top of the bell is near either end, then the picture will either be too dark, losing detail in the shadows, or too light, losing detail in the highlights. When detail is lost in the highlights it is called 'blowing out' the highlights.
Now that you can read the histogram, can it help you improve your photography? Of course!
Using Histogram to Improve Exposure
When you know what the histogram means, you can use that information to set the exposure and change the histogram. You can shift the histogram using your camera's exposure setting and retake the photo. Increasing exposure brightens the picture, shifting the histogram right. Decreasing exposure shifts it left.
Sometimes the graph is more like a pillar than a bell. If the pillar is near the center of the graph there are no highlights or shadows. For the best picture shift the graph as far right as you can without blowing out any of the highlights. This works because digital camera’s capture more information at brighter exposures. The same technique can help if the most of the data is on the left side of the graph. When shifting to the right be careful not to blow out the highlights.
Sometimes all the data in a histogram will be on the right side of the graph, or there will be a pillar on the right. That can indicate blown out highlights. Decreasing exposure can shift the graph to the left and bring out details in the highlights if the highlights are not so bright the camera sensor cannot record the details.
Photography histogram isn't just a tool on your camera. Most photo editors - Photoshop or The GIMP, for example - can also show your photo's histogram. Using the histogram and the editor’s ability to adjust many different photo attributes you can rescue bad - and sometimes seemingly doomed - photographs. The histogram gives you a quick look at what is wrong and right about the photo. Once you know the problems, you can fix them.
The histogram is a powerful tool that is often misunderstood. It looks daunting, but is simple once it is understood. Using it will help you know if a photo needs more exposure, less, or is good at the current setting. It won't guarantee good photos, but with practice it can make taking good photos easier.