Making Sense of Histograms
In case you haven’t noticed, the LCD screen on the back of your digital camera is not a very good tool for judging the exposure of your shots. It’s great for looking at composition, but you need something more accurate to tell if you have exposed your shots correctly. The tool you are looking for is a histogram and more and more digital cameras are including it in their feature set. Scary at first, but if you understand how to use the histogram, it will become your best friend.
The histogram is just a graphical representation of the pixels in your photo. The left side of the graph is the darkest black your camera can reproduce, and the right hand shows the brightest white. Up and down shows how many pixels there are of that brightness. This first sample photo and it’s histogram shows a well exposed photograph with nothing running off either end of the scale.
The second example shows a histogram of an over exposed photograph. Notice the pixels are all bunched up on the right hand side and appear to run off the edge. In this case there are lots of pixels brighter than your camera can reproduce and are displayed as pure white. This photo is REALY burnt out, with no information in the bright areas. We would not be able to do anything to save this photograph as the bright pixels have no information, they are ‘clipped’.
The opposite is true as well. In an underexposed photograph, all the pixels are bunched and run off the left edge of the histogram, clipping the blacks. Again there is nothing we can do to save this photo as there is not enough information to make it appear correctly.
There are some times when you really do want your histograms to look lopsided. When I photograph people on a white background, I deliberatly over expose then background so it will turn out white. The histogram is then weighted to the right. And the opposite is true for a photograph with many shadows and blacks.
You have to look at your scene, see the highlights and shadows, then see if the histogram matches what you are trying to capture.
One more thing to keep in mind; The sensor inside your camera works more efficiently, with the least noise, at the upper (right) 25% of the histogram. If you have the option of bumping your exposure to be a bit so the histogram shows more to the right, without clipping the highlights, your photos will be the best your camera can produce.
It takes some practice to see what your histogram is showing you, and more time yet to be able to have faith and trust in it’s results. After a while you won’t worry how the image looks on the camera screen, as long as the histogram says it’s OK. You will find it is time well spent.
Happy shooting!
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