LUT is the short form of «Look Up Table» and is basically a preset which can change the color settings of photos and videos. Usually they are used for video footage, but by using Photoshop, you can also apply LUTS to your images.

A Look Up Table, or LUT, is essentially a digital file that transforms the color and tone of your image. It essential can convert colors and details in a source file to a new destination state. For example, you can use a LUT to convert a modern digital photo to the color and tone of an older film stock. Or perhaps to convert between a color image to an aged black and white treatment.
A LUT essentially transforms tone and color based upon settings chosen by the creator of the LUT. Each RGB combination of color has a new value assigned.

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