The Levels Adjustment Layer can be used for contrast control and color correction. It’s an incredibly versatile tool. In any well-exposed image, it’s totally feasible that with a few simple adjustments in levels, your image can be ready for print.
One can click the “New Adjustment Layer” button within the Layers Palette, and choose Levels within the drop-down list. You may also navigate to the “Layers” menu ->”New Adjustment Layer” and choose it from that menu.
Levels Adjustment Layer – Photoshop CS4 – Photo Editing Basic Part 3
YouTube - Photo Editing Basics Part 3 - Levels Adjustment Layer White Balance
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One can click the “New Adjustment Layer” button within the Layers Palette, and choose Levels within the drop-down list. You may also navigate to the “Layers” menu ->”New Adjustment Layer” and choose it from that menu.
Find out more about Levels Adjustment Layers Here