Now we’re getting somewhere. What in the world is a histogram and why do I need to know that? Well, first, I’m going to explain what a histogram is, and then I’m going to show you how it can help you when you’re taking photos.
First of all, what’s a histogram?
Basically, a histogram is a visual representation of the exposure via the spectrum of colors in your photograph. It looks like a bell curve. The darker colors in an image show up in vertical lines on the left of the histogram and lighter colors show up as vertical lines on the right. All other colors show up in-between. The important thing to remember, is that in every image, there should be some representation of colors along the entire bottom of the histogram width.
Let’s look at some examples.
Here is an example of a high-key image. High key means there is more light than dark in the (correctly exposed) image.
Here is that image opened in PS Elements. You can see the histogram in the top right corner.
If you look carefully at the histogram, you can see that the colors in the image are all represented all the way across the bottom of the histogram. Those are my daughter’s dark hair, her clothes, the yellow sled… all that. The histogram has a high concentration on the right hand side because of all the white snow in the image. So even though the curve doesn’t line up in the middle of the histogram, this image is correctly exposed because it covers the entire width of the histogram, and it’s obvious that the white snow is what caused the histogram to be heavy on the right.
Here’s an example of a low key image. The colors are mainly dark – but it’s also correctly exposed.
Here is that image along with its histogram:
Here, the histogram builds up on the right hand side, because primarily the image is dark. If you look closely though, there is a small bit of data all along the entire width of the bottom of the histogram. The image is still correctly exposed.
Here is a correctly exposed image with all sorts of colors – light, dark, and in-between. Note the histogram.
So, hopefully, what a histogram shows you is starting to sink in. If not, read over all that again, and if it still doesn’t make sense, please feel free to ask me questions in the comment section.
Now, I’d like to show you how using the histogram on your camera while you’re shooting can help you take correctly exposed images.
I took three images of a jar of flowers. The colors are mid-range colors, so they should show up in the middle of the histogram. One image was correctly exposed. One was one stop underexposed and the third was one stop overexposed.
On most SLR cameras, there is an option to look at the “info” when you’re previewing the image. Did you ever notice the nifty little histogram on that info screen? This histogram is far more reliable in judging exposure than just looking at the image on the LCD screen — especially when you’re outside and it may be hard to judge how light or dark the image is on the screen.
So, here is the underexposed (not enough light) image:
And when I look at the back of my camera at this image (and click the “info” button), this is what I see. Notice the histogram shift to the left, meaning the image is darker than it should be.
Here is the overexposed (too much light) image:
And its histogram. See the shift to the right? There is no data at all on the left side. That indicates they are overexposed. Too much light in the picture.
Here is the “just right” image:
Here’s the histogram. According to this, it looks as if it’s still a tad overexposed, due to the fact that there’s still a little blank space at the bottom of the histogram on the left. But overall, you can see that the histogram covers most of the base, and that base covers the middle section of the histogram.
Hopefully that all makes some sense and you can start to use your histogram as a tool to taking correctly exposed images. Do you have histogram questions? Fire away!