I’ve struggled with the concept of histograms and the associated Photoshop tools, Levels and Curves for quite some time. This and the next couple of posts will demystify these topics beginning with histograms.
Disclaimer: I am by no means a Photoshop guru, expert, teacher or anything of the sort. I’m a lifelong student studying to understand the concepts that will make me a better photographer. When in doubt Photoshop Help is the place to go.
What is a histogram?
A histogram is a bar graph that illustrates how pixels in an image are distributed by graphing the number of pixels at each tone and color intensity level. The histogram graph looks like a mountain peak, or a series of peaks. The more of a particular tone/color, the taller the peak.
Where are histograms found?
You’ll find histograms in the following places:
- Playback mode of digital cameras
- Lightroom Develop module
- Photoshop, Photoshop Levels tool, Photoshop Curves tool
How do you read a histogram?
Along the X-axis (horizontal) of the graph indicates the range of tones in the image. The left side of the histogram is dark (pure black on the far left), the right side is light (pure white on the far right), and the middle are the mid-tones. The position of the values along the Y-axis (vertical axis) is how many pixels are present at a particular tonal value. In other words you can determine how many darks, mid-tones, and lights are in an image.
How are histograms used?
One use of an image histogram is to determine the exposure of a digital image. An underexposed image has a curve that has values bunched up or spiked to the far left. An overexposed image has a preprominence of values far to the right.
Note to self: turn on RGB highlights to view blinking of overblown highlights. Pure white cannot be recovered no matter how good you are in Photoshop. You have a better chance at recovering shadow detail albeit you may have to sacrifice a bit of grain. Or you can take 2 pictures e.g. exposing for sky, then exposing for landscape, and combine in post, but I digress.
Why concern yourself with histograms?
Histograms are your friend because everyone wants to capture a good exposure in camera. Trust me!
It’s important to note there’s no right or wrong histogram, no ideal shape. They are easy to read displays of information about your image.
Below are images and their corresponding histograms. Hover over image to reveal caption.
Check your camera’s histogram to avoid missing those great shots!