Discover
learn. create. do.

How to Read a Histogram (Without Getting a Headache)

by Hillary Grigonis
featured, photo & video, Photoshop Week

Sure, peaking at your LCD screen offers a glimpse at whether or not your image was drastically over or under exposed. But, when it comes down to whether or not the smallest details are beautifully intact or blown out into a white mass, a simple peek at the preview doesn’t cut it.

A histogram gives photographers a more accurate representation of an image’s exposure by putting all the pixels on a chart. From helping photographers judge an exposure in the field to assisting the editing process, histograms can be a valuable — yet confusing — tool. Detangle the mystery with a step-by-step guide on how to read a histogram.

So, what’s a histogram?

A histogram arranges all the pixels into a chart based on their brightness or color, with the darkest pixels on the left and the lightest on the right. Histograms give photographers an idea on whether their exposure is accurate as well as if further adjustment to the scene’s lighting might be necessary.

A luminance histogram places all the pixels on a chart adjusted for human eyesight and accurately depicting both true white and true black, but otherwise doesn’t include color data. An RGB histogram, the one displayed in Lightroom as well as on most camera models, includes color data so it’s to see that, if there’s a problem, it might be in that green grass or the blue sky.


Photoshop Week 2017

Its here – Photoshop Week 2017 is on live right now. Whether its histograms or anything else you need we’ve got it with 42 classes covering all things Photoshop — and its free — watch live classes now

Looking for a great resource guide to round out your post processing reading? Check out our Complete Guide to Post Processing.


Step 1: Find the histogram.

Histograms are typically available inside any camera with manual modes, though the exact location varies on the model. Histograms are typically accessible by accessing an image in preview and shifting through the view options with the arrow keys — you also may need to turn the feature on in the camera’s menu. On some models, the histogram is also offered in Live View. If you’re not sure, consult your camera’s manual.

While editing, histograms can also be helpful — it’s that graph in the upper right corner of Lightroom’s Develop module. Or, you can access it in Photoshop from Window > Histogram.

Step 2: Determine the “clips.”

With histograms arranging pixels from dark to light, what you need to look for first is to check to see if any of those pixels are cut off on either side. If the pixels, whether just a few or or large peaks, go off either edge of the histogram, the exposure is leaving out details that you won’t be able to recover in post processing.

If the pixels are cut off on the left, your exposure is too dark — you’ve clipped, or left out, the shadows.

If the pixels are cut off on the right, the exposure is too light and the details in the brightest parts of the image are likely obscured.

Once you see clipping, adjust your exposure so that all the pixels are on the chart, like this:

Step 3: Evaluate the tones.

The edges of the histogram tell you if you’re exposure is off, but the rest of those peaks and valleys give you an idea of that photograph’s dynamic range, or the range of light that was captured. Adjusting the exposure will widen those peaks and change their location, but the histogram can also offer clues on whether you need to add more light into the scene.

With the pixels arranged from dark to light, the histogram also charts the image’s blacks, shadows, midtones, highlights and whites, with the blacks and whites being those extreme edges. Outside those edges, the histogram can tell you if your tones are evenly distributed. In even lighting conditions such as a cloudy day, the histogram will peak in the middle and tapper off on the sides, while on a sunny day, you’ll notice peaks in the highlights and shadows but fewer midtone pixels.

For example, this histogram suggests that the highlights are largely missing and that the photo contains lots of shadows and a few overexposed whites but not much in between:

 

That tells me that my camera isn’t capturing the dynamic range of the scene very well. So, I took that same scene and added a fill flash, then ended with with a histogram that’s still missing a few tones but it looks like this:

Where the peaks in the histogram are can give you clues as to how you could improve your image. If you’re missing the midtones or have lots of shadows, try adding a fill flash. If you have plenty of highlight peaks, try lowering the exposure of just the sky with a graduated neutral density filter. When those options aren’t available, using the high dynamic range technique is another option.

Of course, that’s all assuming you are trying to shoot a colorful, evenly light image. If you’re going for a dark moody shot or silhouette, you’ll want more peaks to the left. If you want a light and airy photo or high key shot, you’ll want more peaks to the right. But, looking at the histogram offers a quick glimpse as to whether or not you’ve successfully captured an evenly lit image, a dark one or a light one — and if that’s not what you intended, gives you a chance to fix the issue.


Photoshop Week 2017

Its here – Photoshop Week 2017 is on live right now. Whether its histograms or anything else you need we’ve got it with 42 classes covering all things Photoshop — and its free — watch live classes now


Step 4: Check the contrast.

Just how wide those peaks are indicates how much contrast the image has. Peaks that gain height quickly have less contrast while peaks that slowly build from the edges indicate an image with lots of contrast.

Again, whether or not you choose to make adjustments based on this information depends on the look you are going for — soft beauty lighting will have less contrast than a dramatic portrait with hard light and that’s okay. What the histogram does is show you whether or not you really achieved that goal so that you can adjust the lighting or camera settings as you shoot.

The histogram can help guide your camera settings in the field as well as influencing which adjustments you make in post — but only if you understand how to read one first.

Looking for a great resource guide to round out your post processing? Check out our Complete Guide to Post Processing.

Tags: , , , , ,

Related Classes

Related Articles

Comments

Hillary Grigonis

Hillary K. Grigonis is a web content writer and lifestyle photographer from Michigan. After working as a photojournalist for several years, she made the leap and started her own business and now enjoys sharing tips and tricks with emerging photographers.