A histogram is a graph that shows you information about various tone values in your digital image. The information taken from the picture is placed into gray scale and then interpreted on to this graph. (Now there are some histograms that show colors like red, green and blue; also know as RBG. But, for now lets keep it simple and talk only about the gray scale histogram.) The the left side of the histogram is the darkest gray tones and it transitions across the graph to the right to the lightest gray tones. Below is an example:
There are many things that Histograms can tell you about your image exposure. This graph allows you to know if a pictures is underexposed or overexposed. A under exposed picture will have a histogram that is weighted to the Left, while a overexposed picture will have a histogram that is weighted to the Right. While a properly exposed picture will have histogram in a bell shaped curve with a majority of the peaks in center of the histogram. (see the examples below)
Most photographers do their best not to over or underexpose a picture unless there is reasons to do so for an artistic reason. Histograms make evaluating your work and making slight adjustments that are needed to photos to be exposed properly after they are taken. Over the past year, I used histograms to evaluate my abilities to properly set my camera settings. After taking pictures, I would open this histogram to learn more about how to properly set my camera. I would strongly encourage this is you are also trying to get out of auto preset settings and learn how to manually control your camera settings.
One of my favorite apps to use in editing photos on the go is Snapseed. Inside the app there is a tool called Tune Image. As soon as you open it up you will see a histogram in he lower left hand corner of the app. Which allows you to look at the histogram while you are editing your images. Without the histogram, It is kinda like editing photos blind folded moving the slider around until you find what you want to see. Using the histogram the results will not be overexposed or underexposed unless you artistically the look you are going for.
Inside Tune Image you can make adjustments for brightness, contrast, saturation, highlights, shadows and warmth. What exactly do each of these mean?
There are times when this will not hold true. For example, when you take a picture of something that is very bright like a white flower or very dark like a deep purple flower. In this case the histogram might has spikes to the right or to the left, but will extend across the whole histogram.
When the graph does not extend from one side of the histogram to the other side this is call cutting or clipping. Cutting is a loss of information from the photograph. (The examples above do show cutting or clipping.) This information is not able to be retrieved it is just lost information. Most serious photographers choose to shoot in RAW. It is a file type that keeps all the information at the time the photograph was taken. RAW will allow you to make slight adjustment, but it will not replace all the information that is lost at the time of taking the photo. The only way to truly make this better is to learn to take properly exposed pictures to begin with.
You can use information in the histogram to be able to make adjustments to your picture to make sure they are representing the true colors and exposure that was seen when you took it. There is limited adjustments that can be made without distorting pictures so you have to start off with a fairly accurate picture to begin with.
There are many editing programs out there, some have histograms others do not. Some allow you to see not only the gray-scale histogram but a Red Blue Green scale along with the grey-scale. You will just have to find the ones that work best for you!
Reviewing histograms from my photos has really helped me to learn more about my photos and how to get better results in the field. Most DSLR cameras do offer you the ability to review the histogram while taking pictures. I have found this to be helpful when I was first learning my manual settings. I do continue to use it now occasionally to know if I am on target with my exposure in new situations.
The next time you are editing you pictures open up the histogram and see if it helps make your editing easier for you. Definitely, let me know what you think. Do you like histograms? What do you like? What don’t you like? Tell me your thoughts! I always enjoy hearing from you!