Published on 05/27/2006

If you shoot digital, you have a distinct advantage over the film photographer. One of the most helpful features of the digital camera is the histogram, if you know how to use it.

Understanding the Digital Histogram

If you shoot digital, you have a distinct advantage over the film photographer. One of the most helpful features of the digital camera is the histogram, if you know how to use it.

The Digital Histogram is a graph that can be pulled up on the display screen of most digital cameras for every photo taken on that particular camera. It is not nearly as scary and difficult as it sounds. The histogram is really nothing more than a graph that shows how the image has been exposed. In other words, the histogram shows the brightness of the photograph.

If you'll learn how to read a histogram, you'll never need to worry about washed out highlights and blocked shadows again. It's not difficult

Every medium to high-end digital camera incorporates this feature. Many point-and-shoot cameras have it too. Photoshop and Photoshop Elements can also display it. If you don't know how to display it on your camera, take a break, go grab your manual, and learn.

Even though you can't view it on your 35mm camera, the histogram applies to negative film and transparency film as well. To view a histogram of your transparencies or negatives, you'll need to scan them and view the results in an editing program such as Photoshop or Photoshop Elements.

The histogram is simply a graph showing how the light was recorded from pure black to pure white and everything in between.

There's an awful lot of information available in the histogram, but for our purposes, we're going to use it for just one thing, to find out if we've washed out our highlights or blocked out our shadows.

Of course, we don't necessarily want to completely avoid either of those things. We do, however, want to know if we have done them because, if we've totally blown either one, the resulting image will be useless.

As always, there are exceptions to every rule. At times, we may want to push the highlights a little to bring out some detail in the shadow areas, and sometimes we may want to underexpose the shadow areas a little to tone down a washed out highlight.

If we read the histogram it will tell us whether or not we've achieved the results we were looking for, so we can confidently move on to the next shot.

How to Read the Histogram

In the simplest of terms:

The left side of the chart indicates pure black; the right side, pure white; the center of the chart is the mid-range. So:

If you look at the histogram you'll see the background is white. The indicators - the peaks and valleys - are black. The position of the bulk of the indicators and their highest peaks should, in most cases, be close to the center of the chart. If this is the case, you do, for all intents and purposes, have a correctly exposed photograph.

If most of the peaks and valleys are all the way to the left and disappearing off the chart, you know you have underexposed the image and the shadows will be blocked out, but you will have detail in the highlights.

If most of the peaks and valleys are all the way to the right and disappearing off the chart, you know you have overexposed the image and the highlights will be washed out, but you will have detail in the shadows.

Below is a list of some of the other things the histogram can do for us, most of them in Photoshop or Photoshop Elements. Obviously, we can't discuss them here, but you do need to understand just how important the histogram is and how it can help you to improve your photography - digital or film.

· Improve contrast

· Tone down highlights

· Balance Color

· Open shadows

· Lighten or darken the final print

None of these things can be done when you're out in the field. You can, however, set your camera to its review function so that it will display the histogram and you can leave it there. Now, when you take a shot you can quickly check the histogram and know immediately if you've overexposed or underexposed the image. You'll also know if you've washed out the highlights or blocked the shadows.

Suppose you decided you wanted to overexpose the highlights a little in order to capture some detail in the shadows? Or, maybe you wanted to retain the highlights and let some of the shadow areas go dark. Whatever the effect you wanted to achieve, you'll know almost immediately if you got the results you were looking for.

If you missed the shot, you can shoot it again. If you have what you're looking for, you can move on and shoot the next image. If you're shooting the same subject, but maybe from a different perspective of viewpoint, and if the lighting hasn't changed, you don't need to look at the histogram again; you already have the information you need and can continue shooting with confidence.

Often, especially in high-contrast situations, I'll check the histogram after every shot. Then again, when conditions are not so extreme, I'll check it maybe only once in every 50, or so, shots. I do, however, always check it on the first shot of a new location. That, my friends, is crucial. More times than I can remember, that simple step in my routine has saved me from blowing an assignment.

The histogram is an amazingly useful tool. The more you use it, the more you'll like it. Best of all, your photography will improve significantly.

Quick Tip:

Though not as useful as reading and understanding the histogram - but extremely so when you are in a hurry - there is another tool available in most digital cameras. You can set your camera to show "blinking highlights". Do this, and when you look at the review screen, you see the image just as always, but if there are areas where you've overexposed and blown out the highlights, they will blink either red or white, depending upon the brand of camera.