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.\n\nStep 2: The Threshold Layer shows the image as a black-and-white . First we'll locate and mark the white point: Drag the white arrow to the right until only a bit of white remains visible in the image—this will be your white point. Then go to your toolbar and click and hold on the Eyedropper tool, choosing the Color Sampler tool from the pop-up menu.\n\nStep 3: Zoom into the white spot. Then use the Color Sampler tool to click on the spot. This will leave a little target labeled with the number 1 next to it. Now we've marked the white point in the image—the mark will remain until we clear it.\n\nStep 4: Next we'll find the black point. This time, drag the little white arrow in the Threshold Adjustment Layer to the left until you see just a bit of the black. Zoom into a black area, and click again with the Color Sampler to mark the black point with the number 2.\n\nStep 5: Delete your Threshold Adjustment Layer. Note that your point samples remain. Make a Levels Adjustment Layer and select the white dropper (circled). Hit the Caps Lock key to turn your curser into a target, and line it up with your number 1 sample. Click and watch your whites get brighter, and your whole image follow suit. Note: To clear the point sample markers, select the Color Sampler tool and hit the Clear button in the Options Bar.\n\nFinal Step: Click on the black dropper (circled), then click on point sample 2. This is where the big change often takes place—decontaminating the blacks to neutralize color and resetting the tones for more contrast. If your image is too dark at this point, move the gray arrow slightly to the left to brighten the midtones.\n\nF.Y.I. black & white points aren't just for the levels tool: If you prefer making corrections with Curves, you can still employ the threshold Adjustment layer process to find and mark your image's black and white points. then use the black and white droppers in the Curves dialogue box to begin correcting your image. If you can find a neutral gray in your image, and if the black and white points don't correct color enough, use the gray dropper in the levels or Curves dialogue to neutralize your image after you've completed the final step.