Reading histograms is an important skill to acquire in the world of digital photography. Most images from digital cameras will require some amount of post processing, particularly if you shoot raw format. And most of the processing can be done by viewing the aesthetics of the image as you go, but having the ability to read and manipulate a histogram will increase your productivity and output quality.

So what exactly is a histogram? And how the heck do you “read” one? Take this, for example:

At a glance, it doesn’t tell you much. But there are certain things that you can take from the histogram. No, it doesn’t tell you that it belongs to a photo of a deserted trailer half buried in the middle of the desert. It doesn’t tell you if the image is in focus or if your composition is good. It only tells you the tonal values of the pixels contained in the image — blacks on the left, whites on the right.

For this article, I’ll be looking at a black and white image and histogram in order to simplify things. Color histograms work on the same concepts, but with 3 channels rather than one.

MID CONTRAST AND BRIGHTNESS

This is pretty much a straight b/w conversion with no contrast or brightness adjustments. It doesn’t look too bad, but it isn’t terribly dynamic either. And if you look at the histogram, you’ll see that the pixels fall into a centered group with a little breathing room on the shadows and highlights. We’ll use this one as our baseline to compare against. The other histograms will show this in a transparent green.

LOW CONTRAST

You can visually recognize the lower contrast in this image, and that correlates to a change in the histogram distribution. The pixels near the black and white points have moved in toward a neutral gray, which gives the appearance of lower contrast. The whole thing has basically been squeezed to the center.

HIGH CONTRAST

Again, you can visually recognize the higher contrast in this image, and the histogram changed too. The pixels near center have basically migrated outward toward the blacks and whites, thus giving us more contrast. This time we’re squashing pixels from the middle outward.

LOW BRIGHTNESS

Lower brightness is just a shift of tones toward the black region. You can see that the entire histogram has been pushed to the left. Also notice that the tonal range has been decreased, as shown by a narrower histogram.

HIGH BRIGHTNESS

Higher brightness is a shift in tones toward the white region. Here you can see that the entire histogram has been pushed to the right. Also notice that the tonal range has been increased, as shown by a wider histogram.

THE FINAL IMAGE

You can see that I went with a high contrast, high brightness image for my final path. The histogram shows this with the wide tonal range and a heavy concentration of pixels in the highlights.

CAN YOU SEE IT NOW?

This chart shows a combination of contrast and brightness adjustments on the example photo. As you move from left to right (low brightness to high brightness), you can see the histograms shift to the right. As you move from bottom to top (low contrast to high contrast), you can see the histograms widen.

Click the image for a larger version

The reason I’ve posted this article is because I want to get into the topic of manipulating the histogram during post processing — using it to guide you in what adjustments to apply. So the next article will look at how some of the basic adjustments affect the histogram and the image. We’ve already covered contrast and brightness adjustments here, but there are a few others we’ll need to utilize.

In the meantime, here’s some additional reading on the topic of histograms:

Working With Image Histograms
Photoshop Tip: Understanding Histograms
Camera Histograms: Tones and Contrast
A Practical Guide to Interpreting RGB Histograms

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Fantastic post.

January 13, 2010 2:52 pm

Well Brian,
I have a confession to make. I’ve never been a shooter that looked at histograms in-camera…I’m a chimper alright, but looking at histograms? Now in PS, Levels is the first place I go to check the overall image….you can’t get a decent print without a good black and white point….
Great post!
Andrew
TheDiscerningPhotographer

January 13, 2010 3:56 pm


Yeah, I don’t usually check histograms while shooting unless I’m unsure of the scene. Even then, I’m really just looking for clipping or a heavy shift on the exposure. But when it comes to post processing, I always have one eye on the histogram — and that’s what this article is gearing up for in the continuation piece next week.

January 13, 2010 11:17 pm

Sometimes my histogram is really flat, it spreads across the whole range but its height is low. Juts a narror line. I wonder why it happens because I can take a second shot, changing NO settings, and it will be normal (fat).

I have searched this but failed to find an answer. Does anyone know?

January 14, 2010 8:18 am

Great post, Brian; a very useful summary. Looking forward to what comes next.

January 14, 2010 11:06 am

Fantastic post Brian,

I did not know that contrast is related to “stretching” the histogram, but it makes a perfect sense.
Since this post is can be applied to Histograms during shooting process, what you might want to add is the terms overexposed, underexposed, and how does the histogram show that (in terms of clippings). I would consider this post to be a good place to add this info. (a minor update beside high/low brightness would suffice)

January 14, 2010 3:53 pm

Great post – I never really understood histograms, but this certainly made it easier. Thanks a lot!

January 15, 2010 1:12 pm


Thankyou so much for helping me understand this alittle better.

January 30, 2010 7:32 am

Hey Brian, great shot… is that near Salton Sea? I think I may have seen that same trailer.

February 7, 2010 9:22 am

It is! I’ve got a whole set here:
http://www.flickr.com/photos/brianauer/sets/72157614323202666/

And I’m planning on getting back out there in the next few weeks.

February 7, 2010 8:07 pm

Cool, great set. I love that place!

February 7, 2010 9:09 pm




Excellent example and explanation – thanks!

July 4, 2010 8:59 pm

Comment now!