A power tool for fixing low-contrast photos, Adobe Photoshop’s Levels can add natural-looking contrast and remove color casts, simultaneously and in a few steps. Rarely are such hardcore, histogram-based corrections as this one so simple to do.
To accomplish it, we’ll define, then employ, the proper black and white points (i.e., the darkest and lightest spots) in the picture. By using the histogram to make decisions, you’ll get a good, most-likely more neutral result regardless of the color-accuracy of your computer’s display.
These instructions are for Photoshop CS4. Though the technique will work in earlier versions of Photoshop, CS4 integrates Adjustment Layers more seamlessly—other versions require you to exit Adjustment Layers and then return to them when you need to switch tools.
Step 1: Make a temporary Threshold Adjustment Layer. We’ll use it to determine and mark our black and white points for future reference, then toss the layer out. To make one, click on the Threshold button on the Adjustments Panel, or, on earlier versions of Photoshop, use the Adjustment Layer menu in the Layers Panel.