Histograms: A Simple Explanation

Digital Cameras have an important feature that you couldn’t get in the days when film cameras were the only choice.  Now you get instantaneous feed back as to the quality of the exposure when it’s displayed as a JPEG image on your camera’s LCD screen. In addition, cameras give you several choices of information that can be displayed, such as  shutter speed, aperture, lens parameters, “blinkies” called highlight warnings (or highlight alerts) and histograms.   I recommend you set up your camera to be able to view the histogram along with the JPEG.

[At the end of this post there is a Link to a printable PDF copy of the text of this blog]

In my last blog I shared this photo and its associated histogram below.

As I noted then, the photo was underexposed.

Below you will see a series of photos and the associated histograms, each with a different exposure. I had set my camera to shoot in AE Bracketing mode.  Here the camera shoots a series of photos. In this case, three photos are each 1 exposure unit apart (more about how and why you might want to use AE Bracketing in a future blog).

1 Stop underexposed

Normal Exposure

1 stop overexposed

As you can see from the above photos as each gets brighter the corresponding histogram shifts to the right. Ideally, you would like to see the histogram all the way across, but that doesn’t happen all the time. The shape of the histogram is a function of the tones (bright/dark areas) in the photo. I’ll provide a few examples at the end of this blog, so you can better understand this concept.

Now, looking at both the 1 stop overexposed and the normal exposure photo, I decided that the correct exposure should be somewhere in-between. I made the adjustment you see below on my computer using Lightroom/Adobe Camera Raw. I could have accomplished the same correction when I shot the original photo by using the exposure compensationplus-negfeature on my camera. More about the use of exposure compensation in a future blog.

OLYMPUS DIGITAL CAMERA
Corrected Photo + 1/2 exposure unit.

corrected-histogram

Other photos and histograms examples:

The Tybee Island Lighthouse photo is correctly exposed. Notice how the histogram fills almost the entire width.

In this photo, taken at Mount Saint Michel in France, the area on the left side of the histogram corresponds to the dark areas surrounding the opening.  As you see, this area is along the vertical axis and indicates there is some loss of shadow detail.  Here’s another opportunity to use exposure compensation in the field. If you can’t make the correction in the field there is some good news.  It is possible you can recover some of the shadow detail using Lightroom/Adobe Camera Raw or other photo processing software.

The Patton Memorial in Avranches, France is over-exposed.  Here you see the histogram is shifted way to the right.  When this occurs you need to make the adjustment using the exposure compensation feature on your camera.  Why? Because it is almost impossible to recover highlight detail using photo processing software.  You always need to try to expose your photos to the dark side so that the highlights are not over-exposed as in this photo.

 Link to PDF Histograms: A Simple Explanation

Below I’ve provided two links so that you can explore histograms further.

Using histograms in photography from Picture Correct

Using Histograms in Digital Photography from Picture Correct.

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