What does the Levels command do?

The Levels command is used to adjust the overall contrast of an image. It is also used to adjust the distribution of the range of intermediate tones in the image.

The Levels command is used to change overall contrast by:

1. Setting the first tone in the image you want to be pure black.

This is called the black point. Let’s say you have several dark tones in the photo with the pixel values of 20, 15, 10, and 5 (5 being the darkest since black is zero). If you set the black point slider (move it to the right) in the Levels dialog to an Input value of 10, then the dark tone with a pixel value of 10 will be changed so that it has a value of zero (0) and becomes pure black. But, any pixels with a value of less than 10 will also be made pure black. In our example, the tone with pixel value 5 will also become pure black. In this case you will actually be losing valuable shadow detail. Of course, the other dark tones will also lower in value proportionately.

2. Setting the first tone in the image you want to be pure white.

This is called the white point. Similar to the above example but using the lightest tones, if you have light tones with pixel values of 240, 245, 250 (pure white has a pixel value of 255) and you move the white point slider to the left in the dialog so it has an Input value of 245; this pixel value will be changed to 255 and become pure white. Any tones with pixel values between 245 and 255, i.e. our pixel of 250, will also become pure white.

The Levels command is used to change middle contrast by:

3. Setting the middle grey tone point.

The grey slider shown below the histogram graph, see my article on understanding the histogram, in the Levels dialog controls the distribution of intermediate tones. This is known as the grey point or gamma of the image. When you move this slider you are telling Photoshop to change the values of all of the tones between black and white (but not the actual black or white tones). Whichever tone value you align the slider below will be changed to become a middle grey value of 128. So, if you move the slider to the left under the histogram you will lighten all of the tones between black and white. Conversely, if you move the slider to the right you will darken all of the tones.

By adjusting the black and white end points we alter the overall contrast in the image. This is most commonly used for photographs taken in soft, low contrast, lighting such as to be found on an overcast day. Care should be taken not to lose too many of the darkest and lightest tones as this will lose subtle details. By adjusting the grey point we alter the values of the grey tones; either lighter or darker.

There you have the three essential basics of using the Levels command in Photoshop. The Levels command is the easiest of the tone control tools to use and, with the understanding you now have, you will be able to use it much more confidently.

Photoshop for beginners - The 3 Essentials of the Levels Command.

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