I do a lot of what’s sometimes mockingly referred to as “chimping”, looking down at my camera’s LCD screen after taking a shot. Sometimes I’m looking at the picture, more often I’m looking at the histogram.
The histogram is one of the most powerful yet frequently under-used features of high end cameras. Study them long enough at it gets to be like Neo in The Matrix: You can look at the histogram and know whether the photo is good and have a rough idea what it will look like.
At a basic level the luminosity histogram shows the distribution of luminosity values from darkest to lightest. The vertical spikes in the graph show the distribution of brightness levels in that particular scene.
In the example photos I deliberately selected images that were tricky exposures. A fair subject on a white background, brightly lit background with a foreground subject in shadows, and a balanced exposure in daylight so you can compare the histograms.
In my Canon 7D, the histogram is showing a 5 stop dynamic range (different than the displays in the photos). That’s a pretty healthy dynamic range compared to the old days, and yet many photos demand more. To fit a photo into your camera’s dynamic range, you have a few options:
– Use the fill flash on the foreground, essentially moving the darks into your camera’s midtone dynamic range.
– Use HDR techniques to expose for different parts of the photo and merge them digitally.
– Use a Neutral Density filter to crush the highlights and shift the exposure toward dark and middle tones.
– Wait for better light.
Now you might understand a little better why DSLR video shooters always carry a set of Neutral Density filters around. They’re limited to 1/50 of a second shutter speed, which narrows their options for shifting the dynamic range.
Luminosity is only one component of your histogram. In the future we’ll look at even more ways to hack your histograms for better photography.