Adobe Photoshop CS2 On Demand [Electronic resources]

Project 4: Enhancing Image Contrast

Skills and Tools: Curves Adjustment Layer, Layer Masks, and Paintbrush

Contrast enhancement differs from sharpening. When you sharpen an image, you're attempting to fool the eye into seeing a sharper edge. In other words the image looks more in focus. When you enhance contrast, you're attempting to give the image more separation between the shadows and highlights. In other words, you want your whites whiter, and your darks darker. While Photoshop has an Auto Contrast adjustment (click the Image menu, point to Adjustment, and click Auto Contrast), you will gain much more control over the process if you perform the operation using Curves. The technique you are about to learn will give you a greater understanding of how Curves performs, and let you, not Auto Contrast, decide exactly what areas of the image are to be enhanced. You should understand that enhancing contrast essentially, compresses tonal values within the image. This technique is called a standard "S" contrast curve, and will work to increase the contrast on almost any image. Before you get started, remember, if you are too aggressive, the image will being to look a bit posterized, and you will see banding occur within transitional shadows. Therefore, a soft hand on the controls is recommended.

The Project

In this project you'll bump the contrast of a dull image. The process is simple to accomplish, and will help to kick up the contrast values of any image.

The Process

Open the file

colorado_start.psd in Photoshop, and then save it as

my_colorado.psd .

Click the

Create New Fill Or Adjustment Layer button (half-moon icon), located at the bottom of the Layers palette, and then click

Curves .

Create a mid-tone point by clicking on the middle of the diagonal curves adjustment line.

This allows you to lock the mid-tone values of the image.

Create a quartertone highlight point by clicking halfway between the mid-tone point, and the top point on the line.

Create a quartertone shadow point by clicking halfway between the mid-tone point, and the bottom point on the line.

Drag the quartertone highlight point straight up the curves grid (about 1 grid).

Note: If you want to remove a point, click the point and drag it off the grid, or hold the Ctrl (Win) or (Mac) key, and then click the point.

Smart Tip: When you select a point on the Curves grid, you do not have to drag the point using your mouse, instead you can control the active point using your keyboard up, down, left, right arrow keys.

Drag the quartertone shadow point straight down the curves grid (about 1 grid).

Since you locked the mid-tones, you will create what looks like an "S" curved line. This will lighten up the mid-tones of the image, and correspondingly darken the mid-tones.

Continue raising or lowering the quartertone and highlight points until you see the desired results.

Click

OK .

Good to Know: If some of the areas of the images do not need the contrast sharpening supplied by the Curves Adjustment layer, simply use you paintbrush on the built in mask to isolate areas of the adjustment. Remember, painting with black masks out the Curves adjustment to the image, and painting with white restores the adjustment.

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The Results

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Finish: Compare your completed project file with the image in

colorado_fnl.psd .

Tweaking the Image

It's possible that you may need to work with the mid-tone point as well. The mid-tone point will not increase or decrease contrast, but will lighten or darken the mid-tones. Therefore, if after enhancing the contrast of the image, you feel overall it's a bit too dark or light, then click and drag the mid-tone point up or down.

Factoid: The human eye looks for the effect of contrast based on the speed in which tonal values shift. By opening the Curves Adjustment layer, and performing a standard "S" contrast enhancement curve, you are essentially increasing the rate in which the tonal values shift, and fooling the eye into believing there is more contrast.