All Categories : Web Graphics Teach Yourself Photoshop 4 in 14 Days - 5 - Adjusting Color Are you one of those people who likes to play with the color adjustments on the television set? If you are, you're going to be absolutely astounded with Photoshop's color adjustment capabilities. If you haven't a clue as to what we mean by adjusting color, that's okay, too. By the end of this chapter, you'll be able to turn red roses blue, change a sky from mid-day to sunset and back again, bring out the detail in shadows, and manage every imaginable aspect of color manipulation. Photoshop includes a full set of tools for making color adjustments. You can find them all on the Image+Adjust (see Figure 5.1). Some of these terms, like Brightness/Contrast may be familiar to you; others may not. Don't worry. You'll learn about them all in this chapter. Before you start to adjust color, you need to evaluate what kind of color you have in the picture, and how you'll eventually use the image. You learned about color models and color modes yesterday in Day 4, "Color Modes and Models." You know that RGB color is the kind that is displayed on computer screens, and CMYK color is the kind that is printed. If you're going to be adjusting the color in a picture, it makes sense to adjust it according to the way it will be displayed. If your picture is going on a web page, you should work in RGB mode. If it's going to be printed in color, make your adjustments in CMYK mode. If it's going to end up in grayscale, forget about trying to make the sky a perfect blue. Change the mode to grayscale and make the contrast perfect instead. Figure 5.1 The Color Adjustment menu gives you all the tools you'll need. Where's the AutoFix? Unfortunately, there's no automatic "fix everything at once" command, as there is in some of the low-end image manipulation programs, such as Adobe PhotoDeluxe. Perhaps it's just as well, because those "fix-it" commands seldom give you the result you want. Color is subjective. What you may think of as a blue sky may be very different from what I consider a blue sky, and different again from what the person who wrote the fix-up command thinks of as a blue sky. You're really better off adjusting the color, brightness, and contrast yourself. Your goal, after all, is to make your pictures look right to you. The other point to remember about color correction is that you can apply it to the whole picture, selectively to a single area, or to all but a selected area. When you apply a correction to the whole picture, it may 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. Adjusting by Eye The most obvious way to make a color adjustment is to compare a "before and after" view of the image. In Photoshop, the tool for doing this is called Variations. It combines the Brightness/Contrast, Color Balance, and Hue/Saturation tools into one easy-to-use system that shows you thumbnail images that are variations on the original image. You simply click the one that looks best to you. You can choose variations of hue and brightness and then see the result (which Photoshop calls Current Pick) compared to the original. NOTE: If Variations doesn't appear on the Adjust submenu, it's because the Variations plug-in may not have been installed. Consult the Photoshop manual for information about using Plug-in modules. Figure 5.2 shows the Variations dialog box. When you first open it, the Current Pick will be the same as the Original image, since you haven't yet made changes. You can set the slider to the left (Fine) or right (Coarse) to determine how much effect each variation applies to the original image. Moving it one tick mark in either direction doubles or halves the amount. The finest setting makes changes that are so slight as to be almost undetectable. The coarse setting should be used only if you're going for special effects and want to turn the entire picture to a single color. The default (middle) setting is the most practical for "normal" adjustments. Figure 5.2 The six, left-hand thumbnails adjust hue, while the right-hand set of three adjusts brightness. Adjusting Shadows, Midtones, Highlights, and Saturation If you are using Variations to adjust a color image, you also have the option of adjusting shadows, midtones, highlights, or overall color saturation. Shadows, midtones, and highlights are Photoshop's terms for the darks, middle, and light tones in the picture, or what would be black, gray, and white in grayscale. Overall saturation adjusts all of them at once. When you select shadows, midtones, or highlights, you adjust the hue and brightness of only that part of the picture. The advantage here is that you can adjust the midtones one way and the highlights or shadows another way, if you choose. Each setting is independent of the others, and you can, for example, set the midtones to be more blue, thus brightening the sky, yet still set the shadows to be more yellow, offsetting the blueness that they possess inherently. NOTE: Hue refers to the color of an object or selection. Brightness is a measurement of how much white or black is added to the color. Selecting Saturation changes the strength of the color in the image, giving you a choice simply of less or more. In Figure 5.3, I'm adjusting the saturation of this photo. Remember that you can apply the same correction more than once. If, for instance, "Less" saturation still leaves more color in the image than you want, apply it again to get even less. Figure 5.3 Less Saturation gives you a lighter image. More Saturation gives you a darker one. To adjust this image using the Variations command, use the following steps: 1. Open file 05file01 on the CD-ROM. Open the Variations dialog box by choosing it from the Image+Adjust menu. 2. Set the radio buttons according to where you want to adjust: shadow, midtone, highlight, or saturation. 3. Use the Fine/Coarse slider to determine how much adjustment to apply. 4. To add color, click the appropriate color thumbnail. 5. To reduce a color, click its color wheel opposite. To reduce magenta, for example, click green. 6. To adjust the brightness, click the thumbnails for a lighter or darker image. 7. If you're not sure exactly what you need to do, simply click the image that looks most "right" to you. 8. If you think you may have overdone your corrections and want to go back to the original image, press the Option key (Mac) or Alt key (Windows) to change the Cancel button to Reset. This restores the settings to zero and reverts to the image saved prior to changes. (Note: This works with all Adjustment windows.) 9. Click OK when done or Cancel to undo all your adjustments. To compare my version to yours, open file 05file02 on the CD-ROM. Clipping Clipping happens when areas in an image are converted to pure black or pure white. Clipping only takes place when you adjust highlights or shadows, not midtones. A little bit of clipping is okay, and even necessary if you're looking for a full ranges of tones from black to white. Too much clipping means that you have overdone your corrections and need to back off a little. Use the Show Clipping setting to let Photoshop tell you whether you have overdone your adjustments. Areas that are clipped will show up in your thumbnail images as a bright contrasting color. If you decide to select just a piece of the picture to adjust, you'll see only that much of the picture in the thumbnail view. In Figure 5.4, I'm darkening the washed out sky in the desert picture. To do this, I selected the sky with the Magic Wand tool and used the Feather command to help blend the selection back into the picture. (I set it to feather the edges of the selection by four pixels.) With the selection active, I opened the variations box and chose a more appropriate sky color. You can easily see the difference in the Original and Current Selection thumbnails. Try it yourself. You can paint the sky green or orange if blue is too ordinary. Figure 5.4 The thumbnail shows only as much as necessary. Saving and Loading Settings If you have several pictures that will need the same kind of adjustments, make the changes to one of them in the Variations dialog box. Before you click OK, click Save and follow the usual Save As procedure to save the settings file. Then, when you open the next picture, open Variations and choose Load. Locate the settings file you saved and open it to apply the same corrections. Histograms If you ever took a course in statistics, you're thoroughly familiar with histograms as a kind of graph. That's all they are in Photoshop, too. In this case, it's a graph of the number of pixels at each brightness level (or step from black to white) in the image or in a selected area within the image. You might wonder why this is important. The main reason is that you can tell by looking at the histogram whether there's enough detail in the image so that you can apply corrections successfully. If you have an apparently bad photo or a bad scan, studying the histogram will tell you whether it's worth working on or whether you should throw away the image and start over. The histogram also can tell you if you have over-corrected an image and lost pixel values. The histogram has another use, and that is to give you a sense of the tonal range of the image. This is sometimes referred to as the key type. An image is said to be either low key, average key, or high key, depending on whether it has a preponderance of dark, middle, or light tones. A picture that was all middle gray would have only one line in its histogram, and it would fall right in the middle. To examine the histogram for an image, use the following steps: 1. Open the picture on the CD-ROM called 05file03 and choose Image+Histogram (see Figure 5.5). 2. Look at the histogram. The horizontal axis represents the color values from darkest (0) at the left to lightest (255) at the far right. You can see the range as a gray scale beneath the histogram. The vertical axis for each step of the scale shows the number of pixels in the image that have that value. 3. Click OK when you're done. The statistical data shows you how many pixels are included in the image or in the selected sample. The mean is the average brightness value. The median is the middle value in the range of values within this picture. The standard deviation describes how much the values vary. All you really need to know is that, when you look at the histogram, you should see a fairly even distribution across the graph, if the image is intended to be an average key picture. If the picture is high key, most of the lines in the histogram will be concentrated on the right side. If it is low key, most of the values will be to the left. Figure 5.5 has both glaring whites to darken and dark areas that need to be lightened. These are reflected as clusters of lines in the histogram. Figure 5.5 The photo behind this histogram has too many darks. Levels and Curves The histogram tells you what changes you need to make in the image, but it doesn't enable you to make the changes. For that, you need to use Levels or Curves, which are two methods of adjusting the brightness of an image. They accomplish essentially the same purpose, the difference being that Curves does it with more subtlety. Let's start by looking at the Levels window (see Figure 5.6). As you can see, it has the same histogram, without all the mathematics, but with some controls that you can use to adjust the values. Figure 5.6 Be sure to click the Preview box so that you can see the effect of your changes. Adjusting with Levels The Levels window is a tool for adjusting the brightness of an image based on the information in the histogram. Setting the black point (absolutely saturated black) to match the concentration of darkest levels in the image and the white point (completely unsaturated white) to match the concentration of the lightest levels in the image will force the rest of the levels to reassign themselves more equitably. To adjust the brightness using Levels, follow these steps: 1. Open the Levels window by selecting it from the Image+Adjust menu or by typing Command-L(Mac) or Ctrl-L(Windows). 2. Click the Preview box so that you can see your changes in the image window. If you leave this box unchecked, everything on the desktop will change as you move the sliders. 3. In a color image, you can adjust the composite RGB or CMYK color image, or individual colors, by using the Channels pop-up menu. For now, stay with the composite. (You'll learn more about channels later in this chapter.) 4. To set the black point in the image, move the slider at the left side of the histogram to the point at which the dark lines begin to cluster. 5. Set the white point by moving the right-hand slider to the point where the light pixels begin to rise. 6. Adjust the midrange by watching the picture while you move the middle slider left or right. Figure 5.7 shows the settings for this picture. Figure 5.7 Adjusting the darks helps bring out shadow detail. 7. To adjust the contrast in the image, use the sliders on the Output Levels bar. The black slider controls the dark tones. Moving it toward the center darkens the image. The white slider controls the light tones. Moving it toward the center lightens the image. The gray slider controls the midtones. Moving it left or right darkens or lightens the mid-range. 8. Click OK when you're done. You can also use the eyedroppers to adjust the levels. Click on the white eyedropper and click the lightest part of your image. Then click the dark-tipped eyedropper to select it and click the darkest point on the image. If you have an area in the image that seems to be right in the middle, click it with the mid-range eyedropper. NOTE: If you click Auto in the Levels window or choose Auto Levels from the Image+Adjust menu, Photoshop will adjust the levels based on its evaluation of the tonal range. However, this is usually not satisfactory. Try it, but be prepared to Undo. Curves Adjusting Curves is much like adjusting Levels. You can use the Curves window instead of the Levels window to adjust the brightness. The big difference is that instead of adjusting at only three points (black, middle, and white), you can adjust at any point (see Figure 5.8). When you open the Curves window, you won't see a curve. You won't see the histogram either. Instead, you will see a different kind of a graph, one with a grid and a diagonal line. The horizontal axis of the grid represents the original values (input levels) of the image or selection, while the vertical axis represents the new values (output levels). When you first open the box, the graph appears as a diagonal because no new values have been mapped. All pixels have identical input and output values. Figure 5.8 On this kind of a graph, the zero point is in the middle. As always, be sure to check the Preview box, so you can see the effects of your changes. As with the Levels window, you can click Auto or use the eyedroppers to adjust the values. But, since Curves gives you so much more control, you may as well take full advantage of it. Hold down the mouse button and drag the cursor over a piece of the image that needs adjusting. You'll see a circle on the graph at the point representing the pixel where the cursor is. If there are points on the curve that you don't want to change, click them to lock them down. For instance, if you want to adjust the midtones while leaving the darks and lights relatively untouched, click points on the curve to mark the points at which you want to stop making changes; then drag the middle of the curve until the image looks right to you. Dragging up lightens tones, while dragging down darkens them. Figure 5.9 shows what this actually looks like. To get rid of a point that you have placed, drag it off the grid. TIP: To see the Curves displayed with a finer grid, press Option (Mac) or Alt (Windows) and click the grid. You can also use the Pencil tool to redraw the curve. Clicking the Smooth button after you draw a curve will connect disconnected points and smooth out any sharp angles on the curve. Figure 5.9 You can add up to 15 points on the curve. Color Balance In order to really understand color balance, you have to look at the color wheel. In case you don't remember the order of the color wheel, there's a reference in Figure 5.10, and a color version on the CD-ROM (05file04). Figure 5.10 The color wheel helps you visualize opposite colors. Every color on the wheel has an opposite. If you draw a line from one color through the center of the wheel, you reach its opposite. Cyan is opposite to red; green is opposite to magenta; and yellow is opposite to blue. When the colors in the desert scene were adjusted by using the Variations window, I was reducing a color by adding more of its opposite. When you use the Color Balance window to adjust colors in a picture, you're doing the same thing. Increasing the cyan reduces red, increasing red reduces cyan and so on, around the wheel. Figure 5.11 shows the Color Balance window. Color Balance is intended to be used for general color correction rather than correcting specific parts of an image, although you can use it that way by selecting only the part to correct. It's especially helpful if you have a scanned image that is off-color, such as an old, yellowed photograph. It's very simple to apply the Color Balance tools to remove the yellow without altering the rest of the picture. Figure 5.11 Check Preserve Luminosity to avoid changing the brightness of the image. To apply Color Balance, use the following steps: 1. Select the image or portion of the image to correct. Open the Color Balance window by choosing Image+Adjust+Color Balance or typing Command-B (Mac) or Ctrl-B (Windows). 2. Choose Shadows, Midtones, or Highlights. Generally it's advisable to start with midtones, if you are correcting the whole picture, since they comprise 90% of it. 3. Check Preserve Luminosity so that you don't change the brightness of the image as you shift colors. If maintaining the brightness isn't important, don't check the checkbox. Be sure to select Preview so that you can see how your changes affect the image. 4. Move the sliders to adjust the colors. The numbers in the boxes will change to indicate how much of a change you are making. They range from 0 to +100 (toward red, green, and blue) and to -100 (toward cyan, magenta, and yellow). 5. Adjust the shadows and the highlights; then repeat the corrections until the image looks right to you. 6. Click OK to apply the changes. If Color Balance doesn't seem to do what you want, undo it. Remember, you can also adjust the color balance by using the Variations window or by using Curves. To adjust colors with the Curves window, select the color to adjust from the pop-up menu. Lowering the curve adds more of the chosen color, while raising it removes some (see Figure 5.12). Figure 5.12 Removing green effectively adds magenta. Adjusting Brightness/Contrast If you need to make a simple adjustment to the tonal range of an image, for example, if you have a picture that scanned too darkly, the Brightness/Contrast window (Image+Adjust+Brightness/Contrast) is an easy way to adjust everything at once (see Figure 5.13). Instead of separately correcting the dark, middle, and light values, it applies the same correction throughout the image. While this doesn't give you the same control that you'd have if you made the adjustments using Levels or Curves, or even the Variations window, it's quick and easy. Sometimes it's all you need. Many images are improved by just raising the brightness and contrast by a couple of points. As always, be sure to check the Preview box so that you can see the effect your changes have on the image. Dragging the sliders to the right increases brightness or contrast. Dragging them to the left decreases it. If you're not happy with the results you get with this tool, undo your changes and use the Variations window, or Levels or Curves, to adjust the brightness and contrast. Figure 5.13 Use the sliders to adjust the brightness and contrast. Hue and Saturation The Hue/Saturation window is a very powerful tool with a slightly misleading name. Sure, it lets you adjust the hue (colors in the image) and the saturation (the intensity of the colors), but it also gives you control over the brightness. First, let's look at the controls in the Hue/Saturation window (see Figure 5.14). On the left side of the box, you'll see radio buttons and blocks of color. The top button, labeled Master, adjusts all the colors in the image, or selection, at once. If you only want to adjust one color range at a time, click the button for that color. Figure 5.14 The color swatches indicate the range of colors in that family, not specific colors. The Hue slider moves around the color wheel. With Master selected, you can move all the way from red (in the middle of the slider), left through purple to blue or blue-green, or right through orange to yellow to green. The Saturation slider takes you from zero, in the center, to 100% saturated (pure color, with no gray) on the right, or 100% unsaturated (no color) on the left. The Lightness slider lets you increase or decrease the brightness of the image, from 100 through zero in the center, to plus 100 on the right. NOTE: Lightness is technically the same as brightness. The Hue, Saturation, Brightness (HSB) color model uses these terms to define a color, as opposed to the RGB and CMYK models that define it as percentages of the component primaries which, of course, are either Red, Green and Blue for RGB or Cyan, Magenta, and so on for the CMYK model. The sample swatch, by default, shows the foreground color selected. Click any color in the image to place it into the sample swatch. Then you can more easily see the effect that your slider adjustments have on that particular color. Adjusting Hue and Saturation To adjust an image using the Hue/Saturation window, do the following: 1. Open the window by choosing it from the Image+Adjust menu or by typing Command-U (Mac) or Ctrl-U (Windows). Click Preview to see your changes as you make them. 2. Choose Master to adjust all the colors or click the button next to the color you want to adjust. 3. Drag the Hue slider left or right until the colors look the way you want them to. The numbers displayed in the hue text box refer to the degree of rotation around the color wheel from the selected color's original color. 4. Drag the Saturation slider left to decrease the saturation of the colors and right to increase it. 5. Drag the Lightness slider to increase or decrease the lightness of the image. 6. Click OK when done. Changing the Color of a Selected Object Suppose that you want to turn the red flower into a blue flower. It's not especially difficult to do. Using the Magic Wand tool, select the flower. Open the Hue/Saturation window (see Figure 5.15) and change the color with the Hue slider until the flower is the color you want it to be. Adjust the saturation and lightness, if necessary. If the selected item that you want to change has several different shades of a color, select them and change them separately, so the result will be more realistic. Colorizing Colorizing is a way of adding color to a grayscale image. It gives you a monotone effect, which can be quite interesting. You can also colorize a colored image, converting it from many colors to many shades of just one color (see Figure 5.16). Figure 5.15 Feather the edges of your selection so the colors will blend evenly. Figure 5.16 You can use colorizing to apply a sepia tint to a picture. To colorize a grayscale image, use these steps: 1. First, you must convert it to RGB by choosing Image+Mode+RGB. 2. Open the Hue/Saturation window, as described in the previous section. 3. Click the Colorize box. By default, the image will be converted to shades of red with 100% saturation. 4. To change the hue, drag the Hue slider left or right until you find a satisfactory color. 5. Use the saturation and lightness sliders to adjust the brightness and tonality of the image. 6. When you have achieved the effect you wanted, click OK. Understanding Channels Changing channels sounds like something that ought to have you reaching for the TV remote instead of the mouse. However, Photoshop channels are an important concept to understand and one that will help you work with color adjustment, and later on with masks. Each Photoshop image contains one or more channels that contain the color information about the image. Grayscale, duotone, bitmap-mode, and indexed color images all have only one channel, since their color information is limited or nonexistent. RGB images have four channels--one for each color, plus one for the composite--and CMYK images have five. Dividing the color image into channels means that each channel can be edited and modified alone, as well as in combination with the others, allowing you to make extremely complex changes. You can add more channels to an image to store additional information. Channels you add are called alpha channels. Each channel that you add, however, adds to the file size. You can see, and work with, the channels in your image on the Channels palette (see Figure 5.17). Open the Channels palette by selecting Show Channels from the Windows menu. At the bottom of the Channels menu, there are four shortcut buttons. They represent Load Selection, Save Selection, New Channel, and Trash. Individual color channels are listed below the composite channel. Alpha channels appear at the bottom of the list. Each channel is displayed with a thumbnail of its contents. Active channels are highlighted, and all visible channels are indicated with an open eye icon to the left of the thumbnail. Click on the open eye to hide the channel. Click again to display it. Click on a channel thumbnail to make it an active channel. To make a second channel active without deactivating the first, hold down the Shift key as you click the second one. Clicking on the composite makes all of its channels active. You can't edit a channel unless it is both visible and active. Editing affects all of the channels that are active at the time. Figure 5.17 The composite channel is listed first, by default. NOTE: If your channel displays are in black-and-white, and you'd rather see them in color, go to the File menu and select Preferences+Display & Cursors. Click the box to display Color Channels in color. Click OK when you're done with Preferences. Adding a New Channel You can create a new channel in either of two ways. The Channels window has a pop-up menu. The first item, New Channel, opens the Channel Options dialog box (see Figure 5.18). Here you can fill in a name for the channel (if you want something more descriptive than the default numbers), and you can set your other options for this channel. The other way to create a new channel is to click on the New Channel button at the bottom of the Channel menu. It's the second button from the right. This can be scary if you don't know what to expect, since it immediately places the new channel as an active one, and if it's empty, the screen comes up black if everything is selected (or white if nothing is). To prevent this, hold down the Option key (Mac) or Alt key (Windows) as you click the button to open the Channel Options dialog box (see Figure 5.19). If you are adding several alpha channels, make each one a different color, so you can tell easily which is which. Figure 5.18 The Channels pop-up menu also gives you several ways to modify channels. Figure 5.19 Clicking the color swatch opens the color picker. To delete a channel, select it and click the trash button. Copying a Channel There are several good reasons why you might want to duplicate a channel, but the main one is to preserve a copy of it in case you make corrections that end up making the picture worse instead of better. In such a case, you can apply the copy instead and try again. You may want to duplicate alpha channels and store them as a library that you can apply as needed to keep the original image's file size smaller. TIP: File size affects the computer's performance. If things seem to slow down after you have been working for a while, check to see if your file has become unmanageably large. If it has, consider merging layers and deleting unneeded channels. You can duplicate a channel either by selecting it and using the Duplicate command in the channels palette menu, or by selecting it and dragging it either onto the image window or onto the new channel button at the bottom of the Channels window. To duplicate the channel in another image, open both images and simply drag the channel from one to the other. Splitting Channels When you have an image that's made up of several channels, you can split them into separate grayscale images by using the Split channels command under the Channels palette menu. You might wonder what the advantage is to doing this. One good reason is that in Photoshop you often create very large image files. When a file becomes too large, you can't save it, and you can't transport it. In such a case, splitting it into channels reduces the file from one large one to several smaller ones. If you split a 12 MB CMYK file, you'll have four files, each 3 MB. If you split an RGB file with two alpha channels, you'll have five separate channel files. Later on, you can merge them to restore your color image. When you split an image into its channels, the channels are saved as separate files, with the same name plus the channel name. Figure 5.20 shows the results of splitting the image. I've tiled the three new images so you can see all three at once. Figure 5.20 The Split channels command immediately converts your single color image to three grayscale ones. Merging Channels Combining channels has many advantages if you have a grayscale scanner that enables you to scan through color filters to generate color channel images. Many grayscale scanners have this capability. They make three passes over the full-color image with a red, blue, or green filter, and each pass gives you a single channel of the color image. Combining the three scans which, in effect, merges the three channels, lets you display and save the color image as if you'd had access to a full color scanner. The images to merge must fit these criteria: They must all be in grayscale mode. They must all be exactly the same size in pixels. They must all be open on the Desktop. There must be as many channels as are required by the mode into which you want to merge them. To reconstruct a split file, do the following: 1. Open all the channels to be merged. Select one of the grayscale images to be the active document. 2. Choose Merge Channels from the Channels menu. 3. When the Merge Channels window opens, use its pop-up menu to pick the color mode for the merged file. If you have red, green, and blue channels to merge, pick RGB. If you have the four CMYK channels, choose CMYK, and so on. You can only choose a mode that fits the channels you have available to merge. 4. Click OK. 5. A new Merge box will open (see Figure 5.21), confirming which channels should be merged into the new file's color channels. Click OK, and the merged file will open as a new untitled file. Save it before you start to work with it. Figure 5.21 Whichever mode you selected will be applied to this Merge box. Summary Today, you learned to work with color. You learned how to use variations to make simple, "by eye" adjustments, and how to read and use histograms and curves to apply adjustments more scientifically. You learned how to make the sky a perfect blue and the grass a greener green. Now 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 ratio of an image. You've learned about color channels: what they are, how to make new ones, and how to use them. 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 the photos on the CD-ROM and your own favorite images. © Copyright, Macmillan Computer Publishing. All rights reserved.

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