The lowly Histogram is truly a functionless graph that merely monitors the tonal distribution of an image. It functions much like a thermometer in that it reports the current condition of the image. And it only reports one aspect of the image:luminance. Even when you view individual color channels, the graph only reflects the relative (dark-light) range of the color’s values. The image’s color issues (saturation and hue) are not addressed directly, though changing either will influence the luminance.
The Histogram cannot alter an image’s condition, it simply reflects any changes to the tonality made by adjustment tools. It has one spectacular feature that makes it my very favorite diagnostic tool; it can literally see in the dark.
My first peek at shots on my camera’s memory card happens in the camera, right after I finish shooting each subject and just before I put the camera back in the sling. The second look happens when I’m culling and transferring images onto my computer. This second look is usually an evaluation of content and composition more than exposure. I can usually tell which shots are preliminary keepers by viewing the collection from a very impersonal and objective viewpoint. If the shot doesn’t speak to me at first glance, I’m quick to erase it (both RAW and JPEG icons) immediately. Yes, I always capture both file types and yes, I immediately throw out extras. I can’t afford the clutter.
When it comes time to see the keepers at a larger size, my criteria changes to tonal range. Unless the shot involves known and acceptable stark (black or white) backgrounds, I want to know how much elbow room I’ll have to rearrange the tonal range. Most of the time I can tell just by seeing the relative contrast of the image, but many times (and for many reasons), this visual process can be deceiving. This is when I start looking at the Histogram. This graph has its limitations, but the one talent it has is it’s ability to see potential detail beyond what my eye can see.
Here’s a truth you can take to the bank. Even if the image visually appears too dark and beyond repair, if there is a slope, even a steep slope that can be seen on either side of the graph, then both shadow and highlight tonality can be rebuilt.
Put the Histogram to work early in the photo process. Let it diagnose each picture and show you the truth that may be eluding you on the monitor.
That’s the way I sees it. If you have an argument with this position, take it to a higher court! In the mean time, sign up (above right) to get personal notices of future posts. You can’t beat the price.
I enjoy speaking to schools, photo clubs and organizations every month presenting programs on digital photography, post production, and color science. If you’d like me to speak to your group, drop me a line.
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