The photography histogram – a little known tool to help you make better photos.
The photography histogram is one of the most underused features in a digital camera and in editing software. Many photographers don’t even know it’s there.
Understanding how the histogram works is not only of great help when you photograph, but also when you edit your photos.
Difficult light conditions are the most common challenges for landscape photographers. Getting the exposure right can often be a real pain.
Enabling the camera histogram on your LCD can save you a lot of frustration.Let’s take a closer look at some of the features of the histogram and how you can use it in practice.
What is a photography histogram?
The histogram is basically a graphical interpretation of a photo based on the tonal values in the photo. Tonal values are basically how much dark and bright tones in the photo. The horizontal scale shows the entire tonal range from pure black (shadows) to the left to pure white (highlights) to the right.
In an image with a lot of shadows or darker tones, the histogram is distributed mostly to the left. In a photo with a lot of white or bright tones, the histogram is shifted to the right. Depending on your camera there might be only one histogram showing the total tonal range of all colors combined. In more advanced cameras there is also a separate histogram for each RGB color, red, green and blue.
To the left is a RGB histogram showing the distribution of the combined colors in the photo. The histogram to the right is a color histogram showing the distribution of each individual color in the photo. Both histograms are from the same photo and you can see the shape is very similar.
The vertical axis shows the amount of pixels of a particular tone. The higher the peak is, the more there is of this tone or color in the image. The height of the histogram has no technical limit. It has no adverse effect on your image if the histogram reaches the top of the scale. No need to worry about that.
Basically you use the photography histogram to make sure all the tones in the photo are kept within the range of the horizontal axis. You don’t want the histogram to bounce up the left or right sides. If you see a spike to the left, your image is too dark (underexposed). If there is a spike to the right, the image is too bright (overexposed). You ideally want to avoid both these situations.
Histogram and clipping warnings
A great feature of the histogram is clipping warnings. Clipping warnings are like “an alarm” you can turn on and of. There is no alarm sound, but you get the warning as “blinkies” or colored patches on the photo. Clipping warning let you know when you are about to lose details in the shadow or highlight areas in a photo. You can turn on clipping warning in both the camera and the editing software.
In the camera
Highlight clipping warnings - overexposure
When you take a photo in most situations, it’s more important to avoid overexposure rather than underexposure. If the histogram spikes on the right side, details are lost in the highlights. You cannot recover lost highlight details in the editing process. As a help to avoid this, most modern cameras have an option to turn on Highlight warning.
When you overexpose a photo, the overexposed parts will blink when you look at the preview on the LCD. This is a sign you must change the exposure. You can either increase the shutter speed or use a smaller aperture (higher f-number). Alternatively you can dial in a negative exposure compensation until the “blinkies” disappear. When you see “blinkies” the histogram shifted all the way to the right and is bouncing up the right side.
The blinking blacks indicate the photo is overexposed in this area. Typically this happens to the sky which in most landscape photographs is the brightest part. The corresponding histogram in this photo will be bouncing up the right side. When you take the photo you have two tools available to check the exposure - the blinkies and the histogram.
Shadow clipping warnings - underexposure
Shadow clipping warning is not very common in cameras. I am not aware, but there might some having the option available. As long as you watch the histogram and make sure it’s not bouncing the left side, you will be safe.
Check the instruction manual to find if your camera has this feature and how to turn on the clipping warning.
In the editing software
Highlight clipping warnings - overexposure
At the time you take the photo the only thing you can control is exposure. When editing photos you can make additional adjustments, not only to the exposure but to contrast and colors as well. As I already mentioned, if you overexpose in the camera, you cannot recover the lost highlight. These details are gone forever.
If you’re too hard on the sliders, it can result in lost details in shadows and highlights. The clipping warning is a great tool to help avoid this. When highlight clipping warning is enabled, areas where you lose highlight details will turn red. If this happens you need to dial back on your adjustments.
The red overlay indicates the highlights are clipped in these areas. There is no details left. The histogram is bouncing up on the right side. The photo is heavily overexposed.
I this version I have adjusted the highlights and exposure. The red overlay is gone and the histogram is no longer bouncing up on the right side. The image looks better but I could not recover all details in the sky. In this case the errors I did when I took the photo could not be fixed in Lightroom.
Shadow clipping warnings - underexposure
Similar to the highlight warning you can turn on shadow clipping warning. In this case if you lose details in the shadows, the affected areas will turn blue.
The blue overlay indicates there are no details in the shadows. The histogram is bouncing up on the left side.
In this version I increased the exposure and opened up the shadows. The histogram is not bouncing the left side any more. After the adjustment there are details in the water and under the building. The histogram is no longer bouncing up the right side. There is a tint little blue spot left to the far right. This is OK because in this area it is completely dark and it makes no sense bringing out details here.
Practical use of the histogram in the field
In night photography the histogram is useful when you evaluate the overall exposure. In dark conditions, the LCD can trick you. The JPG preview of the photo on the LCD looks nice and bright making you believe the exposure is good. This is not always the case. In the dark, the histogram is a better option to evaluate the overall exposure.
In bright light
Similar in very bright daylight it can be tough to evaluate the photo on the LCD. The histogram is better to ensure your exposure is within an acceptable range.
Extreme contrast scenes
When you photograph scenes with extreme contrast it’s always difficult to know if your exposure is good or not. Anytime you include the sun in the frame the histogram will reach all the way to the right and probably also bounce up the right side. With the sun in the frame, it’s almost impossible to avoid clipping to the right. In this case some clipping is OK.
For a long time, I bracketed most of my shots when I photographed high contrast scenes. After I started to use the histogram, I shoot much fewer brackets than before. You don't need to bracket unless the histogram spikes up on both the left and right side. When this happens you have reached the max of what the camera sensor can record.
You cannot capture such a scene in one shot, so you need to take two or more frames and merge them together, either in HDR software or by using manual blending techniques.
Be aware the histogram can be misleading since it’s rendered from the processed JPG file. You will find there are more data stored in the RAW file than the histogram indicates. In particular this applies to the shadow areas. How much you can recover is dependent on your camera. In general and to be safe you should aim at keeping the histogram within the limits.
Practical use of the histogram when you post process photo
The histogram is useful in the field, but it’s equally important when you post process your photos. Even if you try your best to get the exposure right in camera, you probably need to make adjustments in the editing process as well.
The digital camera sensor is not perfect. In the field, you can only influence on the exposure. You can expose to the left or to the right. Generally you should aim at a histogram as far as possibly to the right, but without clipping the highlights. When you post-process the image you can recover more shadows while keeping the noise as low as possible.
In the editing software, you will often find there are gaps on one or both sides of the histogram. This indicates lack of contrast in the photo. The histogram is useful when you want to close these gaps to increase the contrast.
If you shoot and save your photos as JPG, it’s more critical you get the exposure right in camera. It’s harder to recover lost details from a JPG file because the file contains a lot less data compared to a RAW file. With a RAW file, all data recorded by the camera is saved, and you have much more room for adjustments when editing.
Is there a right or wrong histogram?
It’s easy to think a perfect histogram should be nicely distributed with the main portion of the curve in the center. Reading a histogram without an image does not make any sense. All images are different and thus have a different shaped histogram.
If the overall tonality in a photo is dark, the histogram will naturally shift to the left. Similar the histogram is shifted to the right when the photo contains a lot of bright tones.
The overall tonality in this photo is on the bright side. The histogram is positioned all the way to the right. This is a photo where the histogram is correctly placed to the right. It makes no sense trying to shift the histogram toward the center.
In this photo the tonality is dark. The histogram is placed to the left as expected.
If you have not already you should use the photography histogram both when you take photos and when you post process. If you are a beginner photographer, you will learn a lot from the histogram. In tricky light conditions which are quite normal in landscape photography the histogram is indispensable.
It took me many years after I bought my first digital camera before I understood how useful the histogram. It was when I started shooting at night and realized I always underexposed my photos, I decided to learn about the histogram.
Do you use the histogram? Leave a comment below.