Gamma correction is a technique in Adobe Photoshop CS6 and CC that enables you to adjust how an image is displayed on your monitor. Incorrect gamma settings can make images look too dark or washed out. This does not mean that the gamma setting is the same as the brightness setting, though, as it only adjusts the dark tones. In Photoshop, you can either adjust the gamma of an image directly or via an adjustment layer; the latter method preserves the information on the original layer.
Open Adobe Photoshop, and then open the image for which you want to adjust the gamma levels.
Select "Image" from the menu bar, choose "Adjustments" from the options list, and then select "Exposure." Alternatively, select "Layers" from the menu bar, choose "New Adjustment Layer" from the options list, and then select "Exposure." Click "OK" if you opted for the latter method to create the adjustment layer.
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Click and drag the Gamma Correction slider to the left to increase the gamma levels or to the right to decrease. Keep an eye on the images to see the changes in real-time. When using an adjustment layer, the gamma slider is not on a pop-up window, but on the Properties tab.
Click "OK" when you are satisfied with the gamma levels of the image. When using an adjustment layer, the changes are applied automatically and there is no "OK" button.