How to Read Camera Histogram on a DSLR
In this article I talk about how to read camera histogram on a DSLR. Histograms can be found in almost any modern image editing software, however, understanding the histogram on your DSLR takes some knowledge and practice.
The histogram is split into several areas.
The histogram above shows a well exposed image.
When using the histogram in Lightroom you are able to see where the areas are that are over and under exposed by clicking the two triangles. I talk about using the histogram in Lightroom in my article on understanding the histogram in lightroom.
The majority of digital cameras, can display a histogram. I quite often use mine to check for clipping, especially when I am in manual mode.
Learning how to read camera histogram is really important. However, it took me quite a while to realise just how important or useful accessing my histogram actually was.
The histogram can appear to be rather complex and daunting at first, as is the case with anything new.
In this article, I will try to explain how to read and understand the histogram on your DSLR.
How to Understand Histogram on a DSLR
What Information Does the Histogram Give You?
A histogram is a graphical representation of the tonal values of your image. These tones range from black (0% brightness) to white (100% brightness). As shown in the image above, dark tones are displayed on the left side of the histogram. As you move towards the right the tones get lighter.
The middle portion of the histogram represents mid-tones, which are neutral.
The peaks and troughs represent the amount of tone of that particular lightness. In the image below there are more mid-tones and shadows than whites.
Shadow and Highlight Clipping
If a certain portion of the histogram is ‘touching’ either the extreme right or left hand edges, it will indicate loss of detail. This is usually referred to as ‘clipping’.
Highlight clipping (areas that are completely blown out) occurs if the graph is touching the right side of histogram.
Shadow clipping (areas that are completely black) occurs if the graph is touching the left side of histogram. White or black clipping can be often fixed by altering your camera settings, which in turn will alter the exposure of the image.
This will not work in all cases. For example, if the bright sun is in your image highlight clipping will occur. You can get around this by using filters. Landscape photographers who do long exposures can use x10d filters to reduce the amount of light entering the camera, thereby controlling clipping.
If you are editing RAW files in Lightroom you should read my article for ‘Understanding the Histogram in Lightroom‘
If you want to see whether there is any clipping as you are taking images you need to set your rear screen to display the histogram.
Many of the DSLR cameras have live histograms that react to scene in real time. To engage live histogram, you will need to use the LCD screen of your camera to photograph instead of optical viewfinder (Live View mode).
If your histogram reveals any highlight or shadow clipping, alter your exposure accordingly: to save shadow detail, make images brighter by dialing in positive exposure compensation value (+0.3 or +0.7, for example); to save highlight detail, make images darker by dialing negative exposure compensation value (-0.3 or -0.7, for example).
Exposure compensation is usually set using “+/-” button on your camera. If you prefer to shoot with manual settings, just change the aperture, shutter speed or ISO accordingly. Read this article to learn about using these three exposure settings.
Color Channels
Histograms are known as RGB histograms because they display information for three primary colors – red, green and blue.
You will notice that it consists of several diagrams marked with different colors.
If you see gray, this means that all three colour channels overlap.
Yellow, cyan and magenta appear where only two of the channels overlap.
Histogram and Exposure
I use the histogram as graphical representation of my image exposure. Like a lot of photographers refer to them as either ‘good’ or ‘bad’.
Usually, a ‘good’ histogram would render most tones in the middle portion of the graph, and no or few tones would be found at the extreme edges.
A ‘bad’ histogram would have tones at the very edges of the graph, which would basically mean either underexposure to the point of lost shadow detail (shadow clipping), or overexposure to the point of lost highlight detail (highlight clipping), or even both in a single image.
A simple 3 image test
I thought at this point it might be beneficial to do a quick comparison test to explain what I have been going on about in a visual way. Hopefully it will help you to how to read camera histogram on the fly.
I took a RAW image of a Long Eared Owl and manipulated it in Lightroom to represent three versions of exposure. Version 1 is underexposed, version 2 is overexposed and version 3 is correctly exposed.
Under-exposed Version
The first image shows an underexposed photograph (too dark). As you can see, most of the image lacks any sort of bright detail. The histogram clearly shows the tones stacked to the left, with most tones in the shadow range, and some are even clipped (completely black).
Histogram – Underexposed image
Overexposed Version
It should be perfectly obvious that this image is overexposed (too light). A large portion of the image is blown (completely white) and contains no image detail at all. in this case the histogram confirms that the image is over-exposed, with the majority of tones stacked to the right of the histogram.
Histogram – Overexposure
There are a small number of mid-tones displayed in the histogram? They represent the darker areas in the image.
These tones should be shown at the left side of the histogram as ‘shadows’ in a well-exposed version image.
Correct Exposure
This version of the image is correctly exposed, (to my liking anyway.) I actually prefer my images on the darker side and have to guard against that when I am processing my images for print etc.
Histogram – Correct Exposure
As you can see, the histogram has a far more even spread. The tones are stacked slightly to the left, but I think that this is due to the white elements being very bright and consequently the software has prevented them from becoming blown, or containing no detail. Other than that there is a healthy range of tones and the image looks nicely exposed.
It does help if you understand the relationship between aperture, shutter speed and ISO.
Should you Set your Exposure Based on the Histogram?
Based on these examples, a ‘good’ histogram does in fact indicate correct exposure.
Should you use the histogram to judge exposure?
In my honest opinion, no.
Let me throw a spanner in the works with another image of a Glass Wing butterfly. Let us look at the histogram first.
At first glance you would assume that this image is under-exposed, with most of the tones stacked to the left, representing an under-exposed image.
However, if we look at the image on which that histogram is based it is fairly apparent that it is perfectly exposed.
If we then manipulate the RAW file to get an even spread of tones, this is the result. In my opinion the image is too light. The subject gets lost in the background and a lot of the highlight detail and image definition is being lost on the subject itself.
How to read camera histogram – My Conclusion
I don’t think that the histogram is very good for evaluating your exposure. The accuracy of it depends on too many factors, including the image you are photographing.
The histogram merely shows you the amount of tones of various brightness levels in your image, and nothing more. It is very useful for spotting clipped any highlight or shadow detail at specific exposure settings. You can use it as a guide to avoid such loss of detail as you take pictures, and that is where histogram excels.
At the end of the day it is entirely your choice whether you refer to the histogram or not in your normal photography routine. I tend to use it when I am editing in Lightroom. Using RAW files allows me to change the tonal aspects of the image and gain absolute control over my exposure.
Thank you for reading. I hope it proves useful.
Roger
