Photoshop cs5 cho nhiếp ảnh gia part 45 docx

275 ■ COLOR ADJUSTMENTS 7 Ph oto by Josh An on Color Adjustments Color often creates strong emotional reactions, drawing you into a photo or making you pass it by. Expressive images with the most impact use color wisely to direct our attention and elicit reactions. Nature photographers have more choices to make about the colors in their images than do most photographers. Other types of photographers must maintain neutral colors, but we nature photographers are often looking for color casts, such as the warm glow of early morning light. Although we’re often trying to create as natural-looking an image as possible, we also have a great deal of latitude to modify colors to make our images more expressive. Chapter Contents Recognizing Color Casts Removing Color Casts Adding a Color Cast Modifying Colors to Match Nature or Add Impact Using Layer Masks with Color Adjustments 607343c07.indd 275 4/13/10 2:41:43 PM 276 c h a p t e r 7: COLOR ADJUSTMENTS ■ Recognizing Color Casts Sometimes, despite the fact that you may have previously adjusted the white balance in the raw converter, you may look at your image and decide that the colors just aren’t quite right. You may or may not be able to identify which color is the culprit, but you know something is off. At other times you may not even be aware there is a color cast until you do some checking. There are several ways to detect a color cast. Using Hue/Saturation to Reveal a Color Cast An easy way to identify a color cast is to open a temporary Hue/Saturation adjustment layer—click the Adjustments panel icon , choose Hue/Saturation , and drag the Saturation slider all the way to +100. Although your picture will look weird, this will show you where there are colors that don’t belong. Think for a minute about what col- ors you’d expect to see versus what you do see, since the colors are supersaturated. Pay attention to the hues, particularly in areas that should be mostly neutral (white to gray to black) to determine whether there are unexpected colors appearing. Note: Although it’s possible to create any adjustment layer from the main menu bar—by choos- ing Layer > New Adjustment Layer—we recommend opening all adjustment layers from the Adjust- ments panel or from the icon at the bottom of the Layers panel. That way, you won’t accidentally find yourself choosing Image > Adjustments on the main menu and working directly on your pixels. As an example, Figure 7.1 shows a picture of a snowy egret with no obvious color cast and the same image with the Hue/Saturation slider pulled all the way to +100. Although you expect the water to turn blue or blue/cyan and the sand to turn yellowish, you do not expect the egret to be magenta. Clearly there is at least a partial magenta cast to this image. Figure 7.1 At rst glance, there is not an obvious color cast in this picture (left). Boosting the saturation to +100 reveals an unexpected magenta cast in the snowy egret (right). Ph oto by EllEn Ano n 607343c07.indd 276 4/13/10 2:41:44 PM 277 ■ RECOGNIZING COLOR CASTS Note that early-morning outdoor pictures on what will be a sunny day often have a cyan cast to them. Pictures taken in shade often have bluish casts. Magenta casts are also common, particularly with landscape pictures or images that include a partly cloudy sky. If pulling the Hue/Saturation slider has revealed an obviously problematic color cast, it can be tempting to just go to the channel containing that color and reduce the saturation. Occasionally that approach will work, but the problem is that it reduces the saturation of that color throughout the entire image, even in areas that should be that color. There are several more useful approaches to removing the color cast, which we will describe shortly. After using the Hue/Saturation adjustment dialog box to identify a color cast, click the trash can icon to remove this layer. You need it only temporarily to give you an idea of whether you should consider doing something to remove a color cast. Using the Info Panel to Reveal a Color Cast When we talk about “neutral” in a digital picture, we’re referring to the relationship of the red, green, and blue (RGB) values for any tone, from pure white (where the RGB values are 255,255,255) to pure black (RGB values 0,0,0), as well as all tonalities of gray in between (in which the red, green, and blue values are all nearly identical). Neutral also means that pixels that should be pure red will have an RGB reading of 255,0,0; pure green will be 0,255,0; and pure blue will be 0,0,255. The farther away from these readings any pixel is that should be neutral gray or pure red, green, or blue, the more of a color cast there is. We nature photographers rarely, if ever, need to be concerned with total neutrality. In fact, outdoor lighting almost always imparts a color cast—sometimes warm, sometimes cool. Nonetheless, it’s important to under- stand what neutral would be. Understanding the values that neutral pixels should have enables you to check for a color cast by using the Info panel. To access it, choose Window > Info. If there are any areas of the picture that you know should be neutral (pure white, gray, or black), zoom in and place your cursor over that area. Take a look at the Info panel to see the RGB values of that point. If the pixel is neutral, the values should be all the same (or very close). If one value is higher than the others, there will be a cast in that direction. For example, if an area that should be neutral has roughly equal blue and green values but a higher red value, the picture has a reddish cast. Conversely, if the number for one channel reads lower than the other two channels, the cast is toward the opposite color of that channel. Table 7.1 lists all the ways that one RGB channel might differ from the other two, thus creating a color cast. Table 7.1 Identifying a Color Cast via the Info Panel If This Value Is Off… …This Cast Will Be Seen Red high Red Red low Cyan Continues 607343c07.indd 277 4/13/10 2:41:44 PM 278 c h a p t e r 7: COLOR ADJUSTMENTS ■ If This Value Is Off… …This Cast Will Be Seen Green high Green Green low Magenta Blue high Blue Blue low Yellow In Figure 7.2, a reading taken from the wing of the white pelican should be close to neutral. Instead, it shows markedly lower red values, reflecting a cyan cast throughout the image. Figure 7.2 You know this image has a cyan color cast because the RGB values of a sample from the white wing (point #1 in the Info panel) are 139,152,150. Ph oto by EllEn Ano n Note: Remembering the basic RGB colors (red, green, and blue) and their opposites (cyan, magenta, and yellow) will make your color adjustments much easier and more predictable. Red and cyan are opposites, and green and magenta are opposites, as are blue and yellow. Once you appreciate this fact, you’ll know to add cyan to reduce a red cast, add green to reduce a magenta cast, add blue to reduce a yellow cast, and so on. If you have determined that there is a color cast in your image, you’ll have to decide whether to eliminate it. Not all color casts are bad! Remember that part of the reason many nature photographers prefer early-morning and late-afternoon light is for Table 7.1 Identifying a Color Cast via the Info Panel (Continued) 607343c07.indd 278 4/13/10 2:41:45 PM 279 ■ REMOVING COLOR CASTS the lovely warm (yellow/red) quality it imparts to their subjects as opposed to the more neutral or cooler light that may occur in the middle of the day. Removing Color Casts There are a number of different approaches to removing color casts. Depending upon the individual circumstances, one approach is likely to be preferable in a particular situation, whereas another approach may be more effective in another. For that rea- son, we’ll present several ways to deal with color casts, some of which are objective and some subjective. Note: If while you are shooting you know that you will want to make sure the colors are as accu- rate as possible, take a shot with a gray card or other neutral gray object in the frame. That way, you can use it as the source for the eyedropper and ensure accurate neutral color. Subjective Methods for Removing a Color Cast First we’ll look at the subjective ways to remove a color cast from your image. Some of these approaches allow Photoshop to do most of the work for you, while others offer considerable individual control over the process and invite a great deal of personal preference. Using the Gray Eyedropper If there’s an area that you know should be neutral—it can be any tonality from almost white to almost black and any shade of gray in between—there is a very simple way to eliminate the color cast in your picture. 1. Create a new Levels adjustment layer by clicking the Adjustments panel icon and selecting Levels. 2. Take the time to double-click the word Levels in the Layers panel and rename the layer; we use the name “color cast.” That way, if you return to this file later, assuming you save it with your layers intact, you’ll know exactly what you did in each layer. 3. Click the gray (middle) eyedropper to select it, and then click the area of your image that should be neutral. Photoshop will automatically define the point you click as “neutral” (that is, having equal red, green, and blue values) and will remap the rest of the image accordingly. You can do the same thing using the gray (middle) eyedropper in the Curves Adjustment Layer controls; the results will be just slightly different, since Levels uses a linear algorithm to do the remapping whereas Curves naturally uses a tone curve. Practically speaking, the results will be very similar in most cases. The results are also very similar to using the White Balance eyedropper in ACR. 607343c07.indd 279 4/13/10 2:41:45 PM . in shade often have bluish casts. Magenta casts are also common, particularly with landscape pictures or images that include a partly cloudy sky. If pulling the Hue/Saturation slider has revealed. the Info Panel (Continued) 607343c07.indd 278 4/13/10 2:41 :45 PM 279 ■ REMOVING COLOR CASTS the lovely warm (yellow/red) quality it imparts to their subjects as opposed to the more neutral or. to see versus what you do see, since the colors are supersaturated. Pay attention to the hues, particularly in areas that should be mostly neutral (white to gray to black) to determine whether