One of the best things about digital photography is the instant feedback it gives photographers. You can immediately tell whether or not you ‘got the shot’, especially if you know how to read a photo histogram properly.
Watch the video below or feel free to scroll down and go through the samples.
What is a histogram?
Let’s start with the basics…
A camera’s histogram is an accurate representation of exposure. It illustrates the range of tones (or brightness) present in an image. Reviewing your histogram can help you asses whether you need to make any adjustments to your exposure.
The horizontal axis represents brightness levels (or the tonal range) from the darkest areas (shadows) all the way to the left to the brightest (highlights) on the right, and the midtones in between. The vertical axis displays the number of pixels at each brightness level.
A histogram’s size and shape give you instant feedback on the contrast level of the scene.
Different histogram shapes and what they mean…
Here are a few sample histograms and what their shapes mean.
Underexposed Histogram
As you can see, the histogram here is pushed far to the left into the shadow area of the tonal range almost all the way to black.
It will be difficult to recover data from the shadows in this image, most likely resulting in a very grainy/noisy image.
Best ways to correct the exposure:
- Open up to a wider aperture
- Use a slower shutter speed
- Use a higher ISO
Exposed to the Left (ETTL) Histogram
Not to be confused with the ETTL features on your flash, this histogram skews to the left, which is very common when photographing in darker situations. You will need to be careful raising exposure/shadows in post since you may encounter noise issues.
Slight adjustments aperture, shutter speed or ISO can bring this to a more neutral exposure if necessary.
Neutral Exposure Histogram
This histogram gives us the most data in the midtones of the image. It is also the best way to ensure that you are capturing all the information in the highlights and shadows of your exposure.
An image with this histogram is also the most easily adjusted in post-processing.
Exposed to the Right (ETTR) Histogram
This histogram skews to the right without totally blowing out the highlights of the image. This technique is popular among some photographers as a way to avoid noise in their images.
However, you need to be careful as it is very easy to overexpose your photo further to the right and lose/clip data in the highlights!
Overexposed Histogram
This histogram is pushed all the way to the right, completely blowing out the brightest tones of the photo.
Trying to recover the highlights from this image in post-processing, you will be left with either white or grey areas with totally unrecoverable information.
Best ways to correct this exposure:
- Use a faster shutter speed
- Switch to a more narrow aperture
- Decrease your ISO
Different Scenes = Different Readings
It is important to remember that different scenes will have different histograms, and that is completely natural. If you take a photo in a snow covered setting, you are going to have a lot more detail in the highlights area.
Trust me, I photograph my black dog running through the snow all the time. If you try to push that highlight data closer to the midtone area by changing your exposure settings or in post production, you can make those white areas appear grey.
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