Photoshop CS3: Adjusting Color | Page 4
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Preserving the Original with Adjustment Layers
An important point to remember about color correction is that you can apply it to the whole picture, to a selected single area, or to all but a selected area. When you apply a correction to the whole picture, it might improve some parts and make others worse, so you really need to look carefully at the end result and decide whether the good outweighs the bad.
Fortunately, there's an easy way to apply a correction and then change your mind. One of the best features of Photoshop is the capability to work in layers. (You'll learn all about layers in Hour 11, "Using Layers.") For now, you can think of layers as sheets of transparency film that you place over your image and paint or paste on. If you like what you do, you can merge the layers so that the additions become part of the image. If not, you can throw them away and try again. In addition to the layers that you paint on, Photoshop lets you apply adjustment layers. These work like normal layers except that instead of holding paint or pasted pictures, they hold the color adjustments that you make to the image.
There are a couple of ways to add an adjustment layer to your image. (This is Photoshop. You'll soon find that there are several ways to do almost anything you can think of.) First, and most logically, you can choose New Adjustment Layer from the Layer menu shown in Figure 5.15. They're also on a pop-up menu you reach by clicking a button at the bottom of the Layers palette (look for the button with the half-black, half-white circle) .
Try It Yourself: Using the Adjustments Layer Submenu
To open an adjustment layer:
Click the black-and-white circular icon at the bottom of the Layers palette or choose Layer>New Adjustment Layer (see Figure 5.15).
Select the particular kind of adjustment that you want to make from the pop-up menu. Click OK to open the appropriate adjustment dialog box.
Make whatever adjustments are necessary. You can delete the layer if you're not pleased with the changes, or change the layer opacity to effectively change the strength of the corrections you have made.
The New Adjustment Layer submenu and the Layers palette.
Channels are another way of looking at color. Each image has one or more channels, with the number depending on the color mode chosen. CMYK has four separate channels plus a composite. RGB mode has three plus the composite. Each channel holds information about a particular color element in the image. Think of individual channels as something like the plates in the printing process, with a separate plate supplying each layer of color. You can often create interesting textures or special effects by applying filters to just one channel. Figure 5.16 shows the Channels palette (twice) with RGB and CMYK channels.
You can set preferences to show channels in grayscale or in their colors.
There are also alpha channels, which have several uses. They are used to define the placement of spot colors (Pantone, Focoltone, and so on). They also contain the maps for masks you create and want to save with the image to which you have applied them.
In this hour, you looked at working with color. Variations make simple, "by eye" adjustments, letting you choose from differently enhanced thumbnails. Levels and curves apply adjustments more scientifically. You now know how to make the sky a perfect blue and the grass a greener green. You know that adjusting levels lets you set limits for dark, middle, and light tones in an image. You have learned about color balance and how to apply changes to hue and saturation. You have seen how to change the brightness and contrast of an image.
Color adjustment is one of Photoshop's most-used features, and one that you'll rely on whenever you need to touch up a photo or a scanned image. Practice with it as much as you can, using your own favorite images.
Levels and Curves seem to do more or less the same thing. How do I know which to use?
If the picture seems to have the right color balance (not too red, green, and so on) but is too dark or light, use Levels. If the colors aren't right, adjust the Curves for individual colors and for the RGB (full-spectrum) channel.
I have a sepia-tinted photo (brown tones) that I have scanned into the computer, but the scan came out yellow. Is there a way to get rid of the yellow cast without losing the sepia?
The easy way is to convert it to grayscale so that you get rid of all the color. Then convert the image back to RGB. Open the Image>Adjustments>Curves dialog box. Instead of RGB on the Channels pop-up menu, select red and drag the curve up until you have added an appropriate amount of red. Then set the pop-up menu to green and drag the curve up until you have added enough of that color. Finally, set the pop-up menu to blue and drag down until you have removed the blue and achieved a reasonable amount of sepia. Experiment until you get the color you want, and then click OK.
If the picture's going to be printed in black and white for a newsletter, do I really need to adjust the color balance and stuff?
Always leave your options open. Adjust a copy of the picture in Grayscale mode, just to make sure that the contrast is good for reproduction. For that, you don't need to think about color. But keep a copy in color in case you want to put the same picture on a web page or do something else with it later.
A picture came out too green. What should you do?
Open Variations and choose more red.
Open Variations and choose more magenta.
Say you took it in Ireland.
A picture was taken on a foggy day, and its colors look washed out. Is there any way to fix it?
Increase the saturation.
Lower the lightness.
Paint over the picture with brighter colors.
How can you lessen the amount of change in the Variations dialog box?
Hold Shift+Ctrl+P while you click the thumbnail.
Use the Fine/Coarse slider.
B. On the color wheel, magenta is opposite green, so adding more magenta removes excess green.
A. Weak colors lack saturation. Increasing saturation slightly brightens the picture, but don't overdo it!
B. Moving the slider toward Fine lessens the amount of correction applied each time. (Trying to implement answer A would probably sprain a finger.)
Download some of the photos from the Sams website. To get to the website, point your web browser to http://www.samspublishing.com/. In the Search box, type this book's ISBN without hyphens. On the book's main page, find the link to the download page. Then see how much further you can go. Turn a cloudy day into a sunny one and then reverse it. Experiment. Try your hand at changing the colors by eye, and then see whether you can duplicate your efforts by using the histograms.
This chapter is excerpted from the book titled, Sams Teach Yourself Adobe Photoshop CS3 in 24 Hours, authored by Carla Rose, Kate Binder, published by Sams Publishing, April, 2007, ISBN 0672329352, Copyright 2007 Pearson Education, Inc.