In fact, that display is called a histogram, and for those savvy shooters that know a thing or two about adjusting F-stops, it can be quite a useful tool. On the other hand, for the majority of photographers who buy expensive digital cameras and leave the mode dial on “Auto” for the rest of their lives, the histogram is simply a mountain range — and probably just an annoyance. Ahh, but it’s a useful annoyance!
Just a Simple Chart
On just about every digital camera, the histogram provides a graphical representation of luminance in an image. No matter what the price-point of the camera, it’s a built-in feature that can be enabled or disabled on the LCD display (provided that you can locate that multi-function circular thingy).
Each histogram is essentially a chart, with an X (horizontal) and Y (vertical) axis. For any given image, the X axis represents the distribution of pixels throughout the entire range of luminance, starting with shadows and dark tones on the left, mid-tones and grays in the center, and the picture’s highlights and white regions on the right.
The histogram’s Y axis plots the number of pixels for a particular luminance level — the higher the peak, the more pixels in that given range. Overall, the chart provides the shooter with “status at a glance” regarding the distribution of light. If the majority of vertical peaks are concentrated on the left, the image is most likely dark or under-exposed. If the majority of peaks are concentrated on the right, your image might be over-exposed. But if the graph is evenly distributed, you’ve probably taken an excellent exposure. Yes, there are exceptions, but those are the general rules of histogram interpretation.
Quick Results, Improved Images
With this clever tool in hand, the savvy shooter can make adjustments to a picture’s exposure. For a dark or under-exposed image, a slower shutter speed or a wider iris might be required — and for an over-exposed image, conversely, a faster shutter speed or a smaller iris might be required. All it takes is the ability to read the histogram, adjust the camera’s F-stop, and re-shoot. More improved and balanced exposures are quickly realized — by reading the histogram immediately after a picture is taken.
Specialty shots and highly dramatic artistic shots are certainly the exception, such as the kids in the snow bank or the party snapshot at night — but here, the histogram can also be useful. Even if the histogram’s little mountain range is compressed into a narrow band, an adjustment to the exposure (or an adjustment to the flash) can improve the distribution of tones and the overall quality of the image.
In the sample shot (from our family’s trip to Sedona), I’ve superimposed the picture’s histogram directly from Photoshop, and added labels for clarity. The tones are fairly evenly distributed, from the shadows in the trees to the highlights on the mountainside — and nothing is over-exposed. A few bright clouds could certainly improve the image, but that’s another hour in Photoshop.
The Benefits of Under-Exposure
Some might argue that histograms are really designed for the pros rather than the average point-and-shoot vacationer, and there’s certainly some validity there. Working with high-end cameras, most pros shoot in the “Raw” image format rather than JPEG, essentially putting more detail into each pixel (with larger file sizes as a result). Their workflow takes them to Photoshop and to other professional editing tools, with the final product ending up in print rather than Facebook. This type of photographer relies on the histogram, and purposely under-exposes each image in order to yield up to two F-stops of latitude once the image is opened in Photoshop for “post-production.”
Critical to this workflow is the knowledge that one can never truly fix an over-exposed image, and thus the histogram is the photographer’s key tool for preventing overexposure. Sure, you can dodge and burn the image in Photoshop, but even when shooting in Raw, two F-stops of latitude simply can’t put the tones back into an over-exposed or washed-out pixel. These days, most of us point-and-shoot (non-pro) photographers use some form of image editing tool, and the “underexposure” rule certainly applies to us as well.
Learn Your Tools
So, with this in mind, here’s some homework for you. Before your next series of snapshots, ensure that you RTFM, and locate the camera’s histogram control and the method by hich your camera can adjust F-stops. Yes, Sparkie, you’ll probably have to take the camera out of “Auto” mode.
Next, go out and shoot an event, and check out the histogram after each shot. Observe, adjust, re-shoot, and repeat — and look for the even distribution of luminance throughout the image. Improvements are just a shutter click away.
I almost always shoot in JPEG, but I also know how difficult it is to fix a poorly exposed image. Hmmm — maybe I should practice what I preach?
Paul Berliner is president of Berliner Productions in Davis, CA.
