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235 ■ TONAL ADJUSTMENTS WITH LEVELS Tonal Adjustments with Levels The Levels adjustment provides good basic control over tonal adjustments for your images, with the capability to adjust contrast by independently controlling shadows and highlights within your image, as well as to adjust the overall brightness. In ACR you can make similar adjustments by setting the Exposure, Blacks, and Brightness sliders. However, there are still times you may choose to use Levels within Photoshop, particularly if you want to make changes to only one area of your image. We’ll talk about making localized adjustments later in the chapter, but first we’ll cover how to use Levels to make a global adjustment. We recommend using Levels to adjust contrast and brightness rather than the adjustment called Brightness and Contrast because the Levels adjustment offers far more accurate control of your settings. In addition, you may opt to use Curves to increase the contrast in a particular range of tonalities rather than throughout the entire tonal range. We’ll talk about Curves later in this chapter. The primary component of the Levels dialog box is a histogram display (shown earlier in Figure 6.3) that charts the distribution of tonal values within your image. Those values are represented from black at the extreme left to white at the extreme right. This gradation of tonal values appears as a gradient bar along the bottom of the histogram chart. The shape of the histogram chart tells you about the distribution of tonal values within the image. For example, histogram data that is shifted toward the left indicates that the image is generally dark. However, that doesn’t necessarily tell you anything about the quality of the image; it may simply be a dark scene. Similarly, a brighter image has a histogram shifted toward the right. The key things to watch out for on the Levels histogram are clipping and gap- ping. Clipping is an indication that information has been lost in the highlights or shad- ows of your image. Gapping is represented by gaps in the histogram and indicates tonal values that are not represented in your image. Clipping is indicated on the histogram display by data running off the end of the chart. Clipping may be displayed in two ways. One is as a thin spike at one end of the chart. This is most commonly seen at the highlight end and is often caused by specular highlights within your image, such as reections from water, glass, or metal. In other words, it isn’t necessarily a major problem within the image because you don’t expect to see detail in such highlights. Note: As we mentioned in Chapter 1, clipping seen in a luminosity histogram always indicates that some pixels in your image are pure black or pure white, but clipping in an RGB histogram can occur when one or more channels has a value of 0 or 255. In such cases, there may or may not be black or white pixels in your image. For example, pure red would have RGB values of 255, 0, 0 and would indicate potential clipping at both ends of the histogram, even though the pixels are pure red, not black or white. The histogram in Levels shows RGB information or individual histograms for each of the channels. 607343c06.indd 235 4/12/10 11:42:40 PM 236 c h a p t e r 6: EXPOSURE ADJUSTMENTS ■ The other type of clipping is more likely to represent a problem within your image, especially if it occurs in the highlights where it is usually important to retain detail. In this type of clipping, the data of the histogram gets cut off abruptly at the end of the chart (see Figure 6.4) rather than ending gracefully before the chart ends. If you think of the histogram as representing a mountain range, ideally the mountains should gradually drop down to the atland before the chart ends. If instead the moun- tains end suddenly in a steep cliff, detail is lost in the area that would have gradually lowered to the base of the chart. All pixels within the “missing” tonal values have been clipped to the minimum (pure black without detail) or maximum (pure white without detail) value at that end of the histogram. Figure 6.4 Clipping of data in your image is exhibited by a histogram chart that appears “cut o” at one end, as with the shadows here. Note: Remember, the correct shape of a histogram will vary according to the distribution of tonalities in your image. Not all subjects will have “mountains” as the correct shape of their histogram; some may have an even distribution of pixels throughout the tonal range, others may have several “mountains,” and so on. Refer to Chapter 1 for more information about histograms. Ideally, your image shouldn’t exhibit any clipping when you get started with your adjustments. If it does, it is often preferable that the clipping occur in the shad- ows rather than in the highlights, because your eyes are usually more forgiving of lost shadow detail in a photographic image than of blown highlights. However, be careful not to produce excessive clipping due to inadvertently creating additional contrast as a result of your adjustments in Levels. Note: There are times that you may deliberately create clipping in the highlights or shadows. For example, if you are shooting or optimizing a scenic and the sky is a very light and boring gray, you may choose to let the sky become completely white to make it easier to replace. If you do, make certain you’re not also blowing out highlights in the rest of your subject matter. Similarly, if you are optimizing an image with a silhouette, you may deliberately make the silhouette clipped black. 607343c06.indd 236 4/12/10 11:42:40 PM 237 ■ TONAL ADJUSTMENTS WITH LEVELS Another potential problem to be aware of as you make adjustments is gapping in the histogram. Think of the histogram chart as a bar chart consisting of many nar- row bars so that the final result typically looks like a curving data display rather than one composed of individual bars. However, when gapping occurs, you start to see the individual bars that create the data display, as shown in Figure 6.5. Gapping indicates that certain tonal values are not represented by any pixels in the image (or are repre- sented, but only by very few pixels). Figure 6.5 Gaps in the histogram indicate tonal values that are not represented within the image. Gaps in the tonal values indicate that smooth and subtle transitions between tones and colors within the image may be compromised. Instead of making a gradual change from one value to another with 10 values in between, for example, the transi- tion may be from one value to another without any transition values between them. This lack of smooth gradations is referred to as posterization (see Figure 6.6). This sort of aw isn’t often seen out of the camera, but rather by making strong adjustments in Photoshop, particularly in 8-bit images. It can also develop after resaving JPEGs. Note: Gaps in the histogram rarely occur for 16-bit files because many more values are available than the 256 represented by the histogram display. Sixteen-bit files have 65,536 tonal values per color channel available, compared to 256 values per channel for an 8-bit file. As a result, 16-bit files can lose a significant number of tonal values without obvious gapping or posterization. However, gaps in a histogram are not an absolute indication of a serious prob- lem with your image. Minor gaps only a few pixels wide, representing just a few tonal values, aren’t likely to be visible to the human eye. In fact, it isn’t until the gaps become relatively extreme (at least 10 tonal values) that they are likely to be potentially visible in the final output. Although gaps certainly indicate a potential problem, they don’t define image quality by themselves. If you have significant gapping in an image, use caution not to make extreme adjustments that may worsen the situation, and closely evaluate the final image at 100% magnification to ensure there isn’t visible posterization. 607343c06.indd 237 4/12/10 11:42:40 PM 238 c h a p t e r 6: EXPOSURE ADJUSTMENTS ■ Figure 6.6 Posterization is represented by a lack of smooth gradations within an image. Note: Ultimately your goal is to provide the best-looking image, not the best-looking histogram! So if a histogram exhibits gapping, consider it a caution to carefully check the appearance of your image, but don’t consider gapping a problem if the image looks good. Revealing Detail Nature photographers are often focused on the detail within the image, so tonal adjust- ments frequently revolve around revealing and enhancing detail and texture in the photo. The Levels and Curves adjustments allows you to do exactly that by enhancing contrast and adjusting brightness to reveal the desired level of detail while maintain- ing an appropriate tonality within the image. The chances are you’ll have made these global adjustments in ACR, but we’ll describe making global Levels adjustments first and then explain how to limit them to certain parts of the image. Begin by creating a new adjustment layer for Levels by clicking on the icon in the Adjustments panel to access the Levels dialog. This adds a new Levels adjust- ment layer to the Layers panel, and the Levels dialog box appears. (Elements users should click the Create Adjustment Layer icon at the top of the Layers panel and choose Levels.) 607343c06.indd 238 4/12/10 11:42:40 PM 239 ■ TONAL ADJUSTMENTS WITH LEVELS Note: We make all our adjustments as adjustment layers rather than applying them directly to the background image. This decreases the potential image degradation that occurs as changes are made to the image, as well as making it easy to modify the adjustments. To avoid any confusion when creating an adjustment, we recommend accessing the adjustment layers from the Adjustments or Layers panel rather than from the main menu. For most adjustments with Levels, you need to adjust only three controls; you’ll find all three directly below the histogram display in the Levels dialog box: T• he black-point slider (for shadows) is at the far left. T• he white-point slider (for highlights) is at the far right. T• he midtones slider is in between the two. Together, these controls allow you to adjust the overall contrast (by shifting the black-point and white-point sliders) and brightness (with the midtones slider) of your image with excellent control. We recommend establishing overall contrast before fine-tuning brightness. There- fore, start with the black-point and white-point sliders. These provide contrast adjust- ment by allowing you to vary the amount of adjustment being applied to the shadow and highlight areas of your image. As a result, you can, for example, sacrifice more detail in the shadows to improve overall contrast without losing significant highlight detail. As a general rule, most nature images benefit from having the brightest pixel value set to white and the darkest pixel value set to black, to maximize contrast and tonal range within the image and to ensure that as much detail as possible is visible. In other words, after making adjustments your histogram should stretch (in most cases) nearly the full width of the chart, with few gaps in that range. Obviously there are exceptions to this, but it is a good basic rule. Because you know that the last data point at either end of the histogram chart represents the darkest and brightest pixels, you could make a basic adjustment by dragging the black-point and white-point sliders inward to the point where the data begins at each end of the histogram (see the example in Figure 6.7). Figure 6.7 A basic start with Levels involves bringing the black-point and white-point sliders in to where the data begins on the histogram. 607343c06.indd 239 4/12/10 11:42:41 PM 240 c h a p t e r 6: EXPOSURE ADJUSTMENTS ■ Of course, this is a somewhat arbitrary way to approach an image. Although it indeed produces good results for most images, it isn’t an ideal solution for everyone. We recommend using clipping previews to help you set the black and white points. The Clipping Preview Although a basic visual evaluation of your image while making adjustments with Lev- els is certainly effective, it can be even more helpful to use the clipping preview display available in Levels. This display allows you to see exactly where you are losing detail within your image as you adjust the black-point and white-point sliders. As a result, you can make a much more informed decision about the settings you’d like to use for these sliders. When you start with an image that lacks strong contrast and you want to maxi- mize the contrast without sacrificing detail in highlights or shadows, the clipping pre- view display allows you to see exactly where you’ll begin to lose detail based on your specific adjustment of the black-point and white-point sliders. We recommend adjusting the white point first, simply because highlight detail tends to be the more critical adjustment. To enable the clipping preview display, hold the Alt/Option key while you adjust the highlight slider/white point. Your image display initially changes to a completely (or almost completely) black display. This indicates that no pixel values (or very few) are clipped to white before you make any adjustment. As you continue to hold the Alt/Option key, slide the white-point slider to the left. You’ll see more pixels showing up as you move the slider, as shown in Figure 6.8. As a general rule, we recommend adjusting the white point until pixels just start showing up in the clipping preview, and then back off just a hair. This is the point where you’ve maxi- mized contrast and tonal range within the image, while sacrificing minimal highlight detail. Of course, the benefit of the clipping preview display is that you’re able to make an informed decision about the amount of detail you’re sacrificing to achieve the level of contrast you’d like to see and about that detail’s location. Figure 6.8 Holding the Alt/Option key gives you a clipping preview as you adjust the white-point slider in Levels, so you can see where you start losing highlight detail and in which areas of the image. 607343c06.indd 240 4/12/10 11:42:41 PM 241 ■ TONAL ADJUSTMENTS WITH LEVELS Note: The colors of the pixels that show up in the clipping preview display indicate the color chan- nels that are losing detail within the image. The pixels won’t appear as pure white or black in the image until the clipping preview shows those colors. However, if any channels are clipping, you may be losing some detail in those areas. The process for setting the black point is nearly identical: Hold the Alt/Option key while adjusting the black-point slider, and a similar clipping preview appears, except that now it starts completely (or almost completely) white, with pixels showing up to indicate where you’re losing shadow detail (see Figure 6.9). As discussed previ- ously, we are generally willing to sacrifice more shadow detail as opposed to highlight detail to maximize contrast. The clipping preview allows you to make an informed decision about how much detail you’re giving up with a particular adjustment and the location of that detail, so you can better determine the extent to which you can push the black point to produce the desired contrast level. Note: As you make changes to your image, the histogram in the Histogram panel will dynamically update to reflect those changes. Figure 6.9 The clipping preview, while adjusting the black-point slider, shows you where you’re losing shadow detail in the image. After you’ve adjusted the black and white points by using the clipping preview, you’re ready to adjust the midtones slider for overall brightness. Because this doesn’t affect the extreme tonal values within the image, there isn’t a clipping preview for the midtones slider. You need to rely on a visual evaluation of the image for this adjust- ment. Think of this slider as a brightness control. Moving the slider changes which pixel value within the image should be mapped to a middle-gray tonal value, but the result is a brightness shift. This adjustment doesn’t have any rule of thumb you can follow in terms of positioning the slider at a particular point along the histogram chart, so you need to make a decision based on a visual review of the image. 607343c06.indd 241 4/12/10 11:42:42 PM 242 c h a p t e r 6: EXPOSURE ADJUSTMENTS ■ Within the Levels dialog in Photoshop (but not Elements) there is a drop-down menu offering access to a number of presets. We normally advise adjusting the settings yourself, although the presets can offer a starting place to experiment with different effects. What can be more useful, though, is the ability to create your own presets. If you’re working with a series of images that need a certain type of adjustment, click on the y-out menu and choose the Save Levels preset. Name the preset in the next dialog and click Save. Your custom preset will then be available from the drop- down menu. Note: There is an Auto button that operates based on choices you set in the Auto Options, avail- able from the fly-out menu in the Levels dialog. On some occasions this can be helpful since it can apply a Levels adjustment differentially to each channel with a single click. Try It! To practice utilizing the clipping preview in Levels, open the image Levels on this book’s companion website, www.sybex.com/go/photoshopnature. Use the clipping preview to adjust the white point and the black point, and adjust the midtones slider visually. Photography is very much a visual pursuit, so it makes sense to perform a visual review of the image and decide whether you’re happy with the results of the adjust- ment you’ve made. You may want to back off the adjustments slightly in some situa- tions to minimize the risk of introducing excessive contrast, or in other situations you may want to bring the sliders in just a bit farther to produce stronger contrast. It’s up to you to determine the best adjustment for a particular image. Note: If you’re having trouble making appropriate adjustments, click the Reset button to have all settings in the dialog box return to their default values. When you’ve adjusted all three sliders, you’ve finished the basic tonal adjust- ment with Levels. As with any other adjustment layer, if you change your mind about the adjustment at a later time, you can simply double-click the thumbnail icon for the Levels adjustment layer on the Layers panel, and the dialog box appears, with the slid- ers positioned exactly as you left them. Note: The Levels dialog box also includes eyedroppers that allow you to click areas of your image to automatically set the black, white, and neutral values. We’ll talk more about those in Chapter 7 when we talk about color casts. 607343c06.indd 242 4/12/10 11:42:42 PM 243 ■ TARGETING ADJUSTMENTS USING A LAYER MASK Targeting Adjustments Using a Layer Mask One of the reasons for using the tonal adjustments within Photoshop in addition to those you already made in ACR is so that you can apply the changes to only certain areas of the image. You may want to do this to help emphasize your subject or to reveal detail in areas of your picture that have different lighting. Doing so requires the use of a layer mask to target the adjustment to a particular area of the image. Every adjustment layer comes with a layer mask. It’s the white box that appears in the adjustment layer in the Layers panel, next to the icon for the type of adjustment. The shape of the mask matches the shape of your image, as shown in Figure 6.10. When a mask is active, there is a thin box surrounding the mask icon. The layer mask in adjustment layers is active by default. Figure 6.10 Every adjustment layer automatically comes with a layer mask. Think of a layer mask as a visibility control for the changes you make on that layer. By default the mask is white. Wherever a layer mask is white corresponds to areas of your image where the changes made on that layer will be visible. Wherever a layer mask is black corresponds to areas of your image where the changes will not be visible. That’s the key to understanding layer masks. Imagine superimposing the layer mask over your image—the areas underneath white parts of the mask will show the changes you make on that layer, and the areas of the image underneath black parts of the mask will show no effects of that layer. There are three ways to make parts of the layer mask black that are particularly useful for nature photographers. The first is by creating a selection before you make the adjustment layer, the second is by using the Color Range option within the Masks panel, and the third is by painting parts of the layer mask black. We’ll talk about all of these approaches in more detail. (Since Elements users don’t have a Masks panel, they have only two ways to define a layer mask.) Note: A layer mask identifies which areas of a particular layer will be visible. In this case, we’re talking about layer masks on adjustment layers, so the mask determines where the adjustment applies and where it doesn’t. White on the layer mask indicates areas where the adjustment layer affects the image, and black indicates areas where it does not. 607343c06.indd 243 4/12/10 11:42:42 PM . Exposure, Blacks, and Brightness sliders. However, there are still times you may choose to use Levels within Photoshop, particularly if you want to make changes to only one area of your image. We’ll. sort of aw isn’t often seen out of the camera, but rather by making strong adjustments in Photoshop, particularly in 8-bit images. It can also develop after resaving JPEGs. Note: Gaps in the. Create Adjustment Layer icon at the top of the Layers panel and choose Levels.) 607343c06.indd 238 4/12/10 11:42:40 PM 239 ■ TONAL ADJUSTMENTS WITH LEVELS Note: We make all our adjustments

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