by Zack Schnepf
I think the histogram is one of the most important and useful tools in all of photography. It’s a tool I rely on throughout my entire workflow, but I notice it’s a concept that many students have a hard time fully understanding. It can be confusing at first, but once you understand your histogram, you can master your exposures. In this article I’ll share how I use the histogram and why I find it so usefulI. I’ll discuss how I use it the field and in post production.
What is a histogram, how do you read it, and what information does it gives you? Basically, a histogram is a graphical representation of the tonality of an image. It shows what tones and colors exist in an image and the concentration of these tones. Here is the basic anatomy of a histogram. This histogram is from the image below of First Snow on Gothic Peak. The left edge of the graph represents pure black, any tones beyond the left edge have no detail in them. Conversely, the right edge represents pure white, any tones beyond the right edge have no highlight detail, they are just pure white. The middle of the graph represents the mid tones of the image. So, left to right is the luminosity scale, or how bright or dark the tones are. In this histogram you can see overlapping graphs of the three color channels RGB(red, green, blue) The height of the graphs indicates the concentration of tones of color and luminosity tones. For instance, in the histogram you can see I have a spike in the blue channel toward the left side, that tells me I have a lot of dark blue tones in this image. There is also a spike in the red channel right in the middle which tells me I have a large concentration of red midtones which you can see in the red foliage of the image. The Height of the peaks is not important for judging exposure, so don’t worry how high the peaks are. One of the most important things I look for in the field and in post processing is information that might be getting lost in either the shadows, or highlights. In this histogram you can see that all of the information is being contained. I can tell, because none of the color channel graphs are bumping into either edge. I’ll elaborate on this further in the sections below.
In the field, I rely on my histogram as a guide to give me an accurate assessment of each exposure I capture. One of the biggest mistakes I see when teaching photo workshops is a student judging an exposure using the LCD on their camera. I’ve been burned by this too many times to count. I’ll be shooting in a low ambient light situation, take a quick look at the image on the LCD and think it looks great, but when I get home and view it on my computer I realize it’s way underexposed. The low ambient light makes the image on the LCD seem really bright. The only way to truly judge an exposure in the field is to check the histogram. Below are 2 bracketed exposures of the same scene. One exposed to capture the tones in the bright sky and the other exposed to capture the tones in the foreground area. In the field, the darker exposure looked good on the LCD, you could even see detail in the foreground grasses, but one look at the histogram told me those foreground tones were way too dark. You can see on the histogram for the darker exposure, the highlight detail is being captured well, there is no information being lost in the highlight, but there is a large spike next to the left edge of the histogram. This indicates a high concentration of dark tones that contain very little detail. I wanted to take another exposure to capture detail in the shadows.
This lighter exposure has plenty of detail in the shadows. You can see in the histogram, the detail that was being lost in the shadows is being captured well. There is now plenty of detail in the foreground grasses and stream. On the other hand, the highlight tones are blowing out. You can see there is a huge spike on the right edge of the histogram and it goes right up to the edge and beyond. Anything beyond the edge has no detail in it. This is what is known as a high dynamic range scene. You could try to compromise and get an exposure in between and use Lightroom and Photoshop to recover the tones that are being lost, or you can bracket exposures and try to combine multiple exposures that contain a lot more information. Either way, the histogram is the tool that will tell you if you have captured the information you need, or not.
In post production the histogram helps me determine which tonality adjustments to make. Below is an image captured while teaching a workshop in the Palouse this spring. You can see on the histogram, most of the color and luminance tones are concentrated in the middle and left side of the image. This indicates that it is a low contrast, dark exposure. This is important information to determine what post processing this image needs. I would like to add contrast, but also brighten the image.
This is after one contrast adjustment. I was able to increase contrast, brighten the image, and control some highlights that were getting too bright. You can see the tones in the histogram are more spread out, but the highlights and shadows have plenty of detail information in them. From here I can decide if want to add more contrast. I can also lighten, or darken the overall exposure. Either way, the histogram will help guide me to the finished image.
You can learn more about Zack and his instructional videos on his website
Location: Bend, OR
Zack is an award winning photographer specializing in fine art landscape photography and post processing. “Art is in my blood. My father is a well known poster artist and painter. My mom was a painter, and print maker and my brother is an art director at Facebook. Art is a way of life for my family, and I will hopefully pass it on to my children as well.”
“The love of nature is also something that my family and I are passionate about. I’ve been hiking, biking, rock climbing and backpacking since I was little. From an early age, I learned to appreciate the beauty in nature.”