In this tutorial, we will take a close look at the Levels Adjustment Layer in Photoshop. We will see how levels can improve low-key, high-key, and low contrast photos, as well as how you can use the Levels Adjustment Layer to make color corrections. We will also spend some time in this tutorial explaining a bit about Photoshop’s histogram and how it works. Let’s get started! 


Histogram Details

For more information about Histograms, see this tutorial "What Does a Histogram Tell Us?"

  • Mean: represents the average intensity value of the pixels in the image.
  • Standard Deviation: (abbreviated "Std. Dev.") shows how widely the image’s intensity values vary.
  • Median: is the midpoint of the intensity values.
  • Pixels: tells you how many pixels Photoshop analyzed to generate the histogram.
  • Cache Level: shows the current image cache Photoshop used to make the histogram. When this number is higher than 1, Photoshop is basing the histogram on a representative sampling of pixels in the image rather than on all of them. You can click the Uncached Refresh button to make the program redraw the histogram based on the current version of the image.

If you position your cursor over the histogram, you also see values for the following:

  • Level: displays the intensity level of the area beneath the cursor.
  • Count: shows the total number of pixels that are at the intensity level beneath the cursor.
  • Percentile: indicates the number of pixels at or below the intensity level beneath the cursor, expressed as a percentage of all the pixels in the image.

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