Working with the Histogram in Lightroom
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At the top of the right panel in Adobe® Photoshop® Lightroom™, you'll see the Histogram, which provides a way to review and evaluate the overall tonality of your image (Figure 1). You are probably familiar with the histogram from your digital camera and Adobe Photoshop. It charts the distribution of tonal values within your image, so you can get a general sense of the relative brightness and contrast of an image. The chart starts with black on the far left and white on the far right. If the image is relatively dark, the histogram will be weighted toward the left. If the image is relatively bright, the histogram will be weighted toward the right. A histogram that is relatively tall on the outer ends and not very tall in the middle has higher contrast, whereas one that is not very tall on the outer ends but tall in the middle has lower contrast.
Figure 1: The Histogram provides a graphical indication of the distribution of tonal values within your image.
In this tutorial, you'll learn how to read the Histogram.
Requirements
To follow along with this article, you will need the following software:
Adobe Photoshop Lightroom
Prerequisite knowledge:
None
The Histogram
Of course, most of us make those evaluations by looking at the image itself, and don’t want to spend time trying to evaluate a chart when we can simply look at the image. However, a histogram can be useful for confirming whether any information is clipped, and is therefore an important tool to utilize when evaluating and optimizing your images.
Clipping occurs when detail is lost in the shadows and/or highlights of an image, either because the image was exposed too dark, exposed too bright, or the scene contained too broad a contrast range to capture all detail. Because a histogram charts the relative number of pixels at a given tonal value, you can determine if clipping occurred in your image by seeing whether the histogram chart is abruptly cut off at the edge of the display area for the histogram (Figure 2). If the histogram is cut off in this manner, detail has been lost. With a RAW capture you may be able to make adjustments (discussed later) to recover this lost detail—but if not, there will be areas within the shadows and/or highlights with no texture or visible detail.
Figure 2: A histogram that is cut off at the end (in this case highlights) indicates that detail has been lost (clipped).
Below the Histogram display you'll see that some basic capture data is shown, including ISO setting, lens focal length, exposure time, and aperture setting. These help you to have context around what you’re seeing in the Histogram itself for a given image.
So far I've been talking about how to "read" the Histogram display, but in Lightroom the Histogram is actually interactive. One is the ability to turn on or off the clipping preview display individually for highlights and shadows. When you turn on one or both of these options, you'll see a color overlay on your image showing you where detail has been lost because of clipping. This can be easier than evaluating the Histogram itself, and is more informative in any event because it shows you exactly which area of the image is being affected.
The clipping preview display is toggled by clicking the small triangle that appears at the top-left and top-right corners of the Histogram. The top-left box controls the shadow clipping preview display, and the top-right box controls the highlight clipping preview display. To toggle the display on or off, simply click the box. A white border will be displayed around the box when the option is enabled. If there are actually clipped areas of the image, the highlight box will also be filled with white. Both appear gray with a gray border when disabled. When enabled, the clipping preview will place a color over the image (blue for shadows, red for highlights) in areas that are clipped (Figure 3).
Figure 3: When you enable clipping preview with the boxes in the Histogram, a color overlay indicates which areas of your image have clipped highlight or shadow detail.
As you move your mouse over the Histogram, you might also note that areas "light up" (Figure 4). Specifically, the Histogram is divided into four zones that relate to specific ranges of tonal values. The darkest shadows at the left are identified as Blacks, the medium shadow areas are identified as Fill Light, the middle-through bright range is Exposure, and the brightest highlights are labeled Highlight Recovery.
These might not strike you as the most obvious names for tonal ranges within the image, but there's a good reason they have these names. Those names correspond directly to the names of controls you'll be able to adjust in the Basic section of the panel. In fact, you can adjust those controls directly on the Histogram. When you mouse over the image and an area becomes highlighted, you can click and drag left or right to adjust the slider relating to that area, just as though you were adjusting the slider itself. I'll discuss these controls shortly, but for now just be aware that the Histogram provides an alternate way to make those adjustments that enables you to better think about what tonal range within the image you’re affecting. As you mouse over an area or drag to adjust, you'll also notice that a value is displayed in the bottom-right corner of the Histogram. That value corresponds to the value for the sliders I'll discuss shortly.
Figure 4: When you move your mouse over the Histogram, you'll see a visual indication of the tonal range you’re passing over.
Note: Remember that each section of the panel can be collapsed by clicking on its label or the triangle near its label. This allows you to minimize the space for controls you don’t use often, to reduce the need to scroll up and down through the controls.
Where to go from here
For more information about Photoshop Lightroom, see the following:
