In focus: the histogram

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Winners of the weekly competition receive a 50,000 won store credit at Hyosung Camera and a Babo Shirt. To take part in the competition, simply upload your photo at www.flickr.com/groups/seoulphotoclub - Ed.

Over the past several weeks we have talked about how to gain a little more control over the DSLR by using the different manual modes available. Once we are familiar with the different modes, we can use a couple of other features on our camera to understand a little more about the image we have just taken and to get some finer control over our exposure. The histogram and exposure compensation are two of these features.

Q: What is a histogram?

A: In a camera, it displays the frequency of tonal values in the photo. Basically, it shows how brightness is distributed throughout your image. The left-hand side of the graph shows how much of the image is dark, and the right, how much is bright.

Q: Where can I find the histogram?

A: You can probably access the histogram for a given image by using the "more info" button while you are reviewing your pictures in-camera. All DSLRs and most point and shoot cameras have this feature.

Q: Is there an easy way to illustrate how it really works?

A: You can easily demonstrate by pointing the camera at the sky and taking a picture and then taking a picture in a dark room. If you check out the histogram for both pictures, you will see that the sky picture is heavily weighted towards the right (bright), and the dark image weighted to the left (dark).

Q: Okay, but what use is this to me when I`m taking a real picture?

A: With reference to the histogram, we ideally want to have brightness distributed reasonably evenly throughout the image. Not too far to the left or right. In reality though, brightness is not evenly distributed - there are bright areas and dark areas - so the most important thing to look for on the histogram is if the graph is touching either end of the scale. If the graph touches the left-hand end, dark areas become blacked-out - solid black. And upon reaching the right-hand extreme, bright areas become blown-out - solid white. A little contact at the extremes is ok, but the danger is in getting too much of the image off one or the other end of the graph. In either case, any detail in those areas is lost forever; you can`t get it back using Photoshop or any other image-editing program.

Q: You mentioned exposure compensation earlier, how is this related?

A: Exposure compensation gives us finer control over the exposure of our image. Basically it`s just a lighten (+) and darken (-) control. If your image is too far to the left on the histogram, increase the exposure - lighten it - a little using the exposure compensation and take the picture again. Likewise, too far to the right, use exposure compensation to decrease the exposure, or darken the next image.

The histogram is a very important feature on the modern digital camera. We have very briefly touched on its function here, but I really recommend you look into it a bit further. It will help you understand your images more and you will create better exposures as a result. Like any aspect of photography though, the best way to become better at it or more familiar with it, is to get out there and do more of it.

By Aaron Raisey

(raisey@hanmail.net)