Today I’m going to walk you through using Histogram for your photography edits, with examples from both Adobe Photoshop and Lightroom.
Let’s start with a quick look at what histograms are when it comes to digital photography:
What Is a Histogram in Photography and How to Read One?
A histogram is a very useful way to examine the contents of a digital photograph. It is simply a graph of the distribution of RGB values throughout the possible range of 0-255. In Adobe Photoshop™, the histogram is called “Levels” and can be found in the pulldown menus via Image / Adjustments / Levels or via keyboard with Ctrl / Cmd – L. Lightroom on the other hand displays a Histogram in the top right corner of the Desktop app.
This high key image below shows that the vast majority of the image pixels are above the 50% mark (128). And given the large specular component, there’s a spike of pixels at the maximum 255 value.
Conversely, this low key image shows all of the pixels are below the 50% mark, with the preponderance well below 25%
How to Read the Histogram in Lightroom
Lightroom has a more comprehensive histogram than Photoshop, showing a separate graph for each color channel in your image. Furthermore, it gives you the option to highlight the areas of the photo that are “clipped”, aka too bright or too dark. For example:
As you can see, the blue and red areas represent underexposed and overexposed areas respectively. Lightroom does not allow you to edit the histogram manually (like in the Photoshop example below). Instead, to effectively improve your histogram in Lightroom, you have to go through basic light and color editing and determine which channels to reduce in order to improve the details of your photos.
How to Improve Photo Quality with Histograms
So this all very fascinating, but so far we just learned via the histogram what our eyes already told us – we have one high key and one low key image. However, the histogram can be conveniently manipulated, with the potential to improve our image quality. Let me show you how to do just that using Photoshop.
In the photo below, we have a nice mid-day shot in the Sierra mountains. But perhaps it’s a little more flat than we recall or prefer.
In the Levels control, we can drag in both the upper and lower level end points a little bit toward the center to increase contrast. You can view the effect of your changes, prior to committing with a click on “OK”, by checking / unchecking the preview box.
Getting back to our high key and low key images, these too can also be potentially improved by manipulating the histogram.
On the right, we are making a dramatic change that changes the focus of the image. But if your goal was to highlight the patterns in the glass, this would be a desirable change.
With the low key image, this change represents an obvious improvement. It is worth noting that the improved image is still not great, because the original is so underexposed. I think the expression “you can’t make a silk purse out of a sow’s ear” applies here. The best approach is of course to take a better exposed photo, but that is not always an option, and the Histogram can be used to recover many marginal photos.
One word of caution, manipulating Levels is “destructive” to your photo, meaning it results in pixels being discarded.
Here’s what the histogram looks like after making that dramatic change to the low key image. All the “jaggies” in the histogram represent lost pixels. If it improves the image, then the loss is worthwhile, but there’s no free lunch in image editing.
Photographer’s Note
I took the low key and high key image with my iPhone 12. The image processing in that device is so impressive, I really had to go out of my way to take an under and overexposed photo. It actually captures images better in marginal light than does my eye – amazing!
