Get the Image You Want(c) Essential Photoshop Editing Techniques 2005
Authors: N
 Published year: 2004
 Pages: 23-24/105
Buy this book on amazon.com >>

Use Auto Contrast to automatically correct an image

An old saying goes, "Light is the paintbrush of photography," and it's certainly true. Just as there are many types of paintbrushes, so are there many types of lightsoft light, hard light, directional light, and bounced light, to mention a few. Each influences the mood and quality of a photo.

Light also affects such things as color balance, saturation, and contrast. Many times we're able to control these factors. Color balance and saturation are relatively easy to adjust with filters and exposure, but contrast control isn't. One of Photoshop's great strengths is its ability to adjust image properties, and adjusting contrast is a snap with the Auto Contrast command.

Understanding contrast in an image

Photographers like to think in terms of tones, that is, how bright something is as opposed to how dark it is. Everything in a scene falls into three categories: highlight, midtones, and shadows. When you take a photo, the tones in the photo reproduce relative to their corresponding tones in the original scene.

If the original scene happens to have the same number of tones as can be reproduced by film or an image card, then everything in the original is reproduced exactly the same in the image, and the scene is said to be a normal-contrast scene, as shown in Figure A1 . But most often this doesn't happen. When a scene has fewer tones in it than it can reproduce, it's said to be a low-contrast scene, as shown in Figure A2 . Conversely, when a scene has many more tones than it can reproduce, it's said to be a high-contrast scene, as shown in Figure A3 .


Figure A1.



Figure A2.



Figure A3.


A photo of a low-contrast scene, while containing all the tones of the original, is said to be flat . That's because it contains no true whites, or highlights, and black, or shadows. Everything is simply a tone of gray. On the other hand, a photo of a high-contrast scene not containing all the tones of the original is said to be sharp . That's because it has too many highlights and shadows.

Applying the Auto Contrast command

To adjust the contrast of an image, we simply want to do the opposite of what we see in the scene. We want to increase the contrast of a low-contrast image and decrease the contrast of a high-contrast image. While you can adjust these images manually using the Brightness/Contrast command, typically you'll need to adjust brightness and saturation as well. The Auto Contrast command automatically adjusts everything in one simple step.

To use the command:

1.

Open the file you want to work on in Photoshop.

2.

Choose Image Adjustments Auto Contrast, and your original image, such as the one shown in Figure B2 . It's as simple as that.


Figure B.


Note

You can also use the keyboard shortcut [Ctrl][Alt][Shift]L ( [option][shift]L on the Mac) to select the Auto Contrast command.


Three adjustments in one command

An image that's either too low or too high in contrast can appear flat or sharp, respectively, in highlight and shadow details. A simple way to correct image contrast problems is with the Auto Contrast command. This command adjusts contrast as well as brightness and saturation all in one step.


Add missing detail to your images

As we mentioned, an image is broken down into highlights, midtones, and shadows. The terms refer to relative luminance, or brightness, levels in a scene as well as in an image. Because of the limitations of a digital camera's CCD, all the luminance levels can't be rendered in an image as faithfully as they can be in the original scene.

Highlights that you can observe in a scene often appear as areas void of detail in an image. The same is true for shadows. Shadows, whose details you may easily see in a scene, often appear as very dark or black areas in an image. This isn't a problem if the highlight and shadow areas are small and contain no or very little important detail, but sometimes you can't afford to lose these details. This problem has plagued photographers since the beginning of photography. However, unlike the photographers of yore, you have the digital solution known as Photoshop at your fingertips to help restore poor quality detail in your digital images.

Noise is good

Background noise can make communication difficult if you're trying to converse with someone, but if you add noise to your image's washed-out highlight areas, it can be quite pleasing. For example, you can use noise to fill an overexposed area in an image.

To do so:

1.

Open the file you wish to work with in Photoshop.

2.

Select Window Layers to open the Layers palette.

3.

Double-click on the Background layer to unlock the layer.

4.

Enter a name for your layer in the Name text box of the New Layer dialog box.

5.

Click OK.

Make the selection

Next , we'll select the highlight pixel area to which we want to add noise.

To do so:

1.

Choose the Magic Wand tool from the Toolbox.

2.

In the tool options bar, enter a value in the Tolerance text box. Low values select colors similar to the pixel you click on, while higher numbers select a wider range of colors.

3.

Move your pointer to the middle of the highlight pixel area and click. A selection border appears, as shown in our sample image in Figure A .


Figure A.


Isolate the highlight pixels

Now, we want to copy and paste the selected highlight pixels into a new layer.

To do so:

1.

Press [Ctrl]C ( C on the Mac), and then press [Ctrl]V ( V on the Mac).

2.

Name the new layer Highlight. Next, we'll add the noise to the Highlight layer.

3.

Choose Filter Noise Add Noise.

4.

Set an Amount that's just enough to add a small amount of visual texture to the highlight area (22% worked well for our example).

5.

Select the Gaussian option button, select the Monochromatic check box, and then click OK. In our example, the Noise filter adds a subtle amount of faux detail to the highlight area, as shown in Figure B on the previous page.


Figure B.


Cloning is better

Adding noise to washed-out highlight areas is good, but if you want more than texture, try using the Clone Stamp tool. With the Clone Stamp tool, you can take a sample of an image and use it to paint other areas of the image. This makes it easy to cover highlight areas with more detailed image information.

Set up the Clone stamp

Before we can work with the Clone Stamp tool, deselect the layer visibility, and then create a new layer to work on.

To do so:

1.

Choose New Layer from the Layers palette's pop-up menu.

2.

Enter Highlights 2 in the Name text box in the New Layer dialog box, and then click OK.

3.

Select the Stamp tool from the Toolbox.

4.

Select the Use All Layers check box on the tool options bar.

5.

Select a brush, since the Clone Stamp tool is a paint tool. For our example, we chose a soft, round 35-pixel brush from the Brush Presets Picker on the tool options bar and set the Opacity option to a value of about 20%, since it won't take much to see a result in the highlight areas.

6.

Define the pixel area in the image you want to copy by moving your pointer to an area in your image right next to the highlight area, and then [Alt]-clicking ([option]-clicking on the Mac) on it.

7.

Drag a few brush strokes from the edge of the highlight area toward the center of the highlight area. You don't need to totally fill the area because you want to retain some of the highlight area and not totally eliminate it.

8.

Position your pointer at another side of your highlight and redefine your pixel paint sample when you've finished one side of the highlight area.

9.

Continue in this manner until you've finished, as we did in our sample image, Figure C .


Figure C.


Lost and found

Lost highlight details, although bothersome, aren't necessarily difficult to fix. With Photoshop, you can apply a variety of techniques to restore detail and create a great image. In the Problem : Solution "Restore underexposed shadow detail" at the end of this chapter, we'll look at the other end of the luminance range and show you how to bring your shadow details out of the darkness and into the light.

Get the Image You Want(c) Essential Photoshop Editing Techniques 2005
Authors: N
 Published year: 2004
 Pages: 23-24/105
Buy this book on amazon.com >>

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