Tài liệu Photoshop cs5 by Dayley part 61 ppsx

n Using the Curves Adjustment tool The best way to use the Curves Adjustment tool is to add a Curves Adjustment layer to the image by selecting the Curves tool in the Adjustments panel..

The most powerful tool Photoshop has for adjusting color and lighting is the Curves Adjustment tool The Curves Adjustment tool provides a dynamic and flexible interface that allows you to make dramatic changes to the lighting and color in images Although the Curves Adjustment tool takes a bit of practice and patience to learn, after you are effective with it, you can make changes in images that you may have thought were not possible

The Curves Adjustment tool can be accessed by selecting Image ➪ Adjustments ➪ Curves from the main menu or by selecting a Curves adjustment in the Adjustments panel This section discusses how to configure and use the Curves Adjustment tool to make changes to the color, lighting, and contrast in your images, as well how to configure and use the Auto Curves Adjustment

Cross-Ref

The concept of using curves to adjust color channel levels was introduced in Chapter 4 You should read that

chapter before reading this section because you need to understand the concepts from Chapter 4 to get the

most out of using the Curves tool n

Using the Curves Adjustment tool

The best way to use the Curves Adjustment tool is to add a Curves Adjustment layer to the image

by selecting the Curves tool in the Adjustments panel This loads the Curves Adjustment layer tool shown in Figure 13.31

The Curves Adjustment tool allows you to make adjustments to the composite channel or any sin-gle color channel using the following controls:

l Presets: This allows you to select one of Photoshop’s predefined presets or one of your

own saved ones You can save the settings you make in the Curves tool as a preset by selecting the Save Curves Preset from the Adjustments Panel menu Photoshop provides the following predefined adjustments to quickly adjust the levels of images: Default, Color Negative, Cross Process, Darker, Increase Contrast, Lighter, Linear Contrast, Medium Contrast, Negative, Strong Contrast, and Custom

l Color channel: This allows you to select the composite channel or one of the individual

color channels Making curves adjustments to the composite channel changes the entire image Making changes to an individual color channel allows you to fix level problems associated with specific color without affecting other colors

Caution

Adjusting the curves of color channels separately changes the color composition in the image If the general

color tones match up well, you should not change the levels of the color channels separately because you may

end up with a color cast or some colors that do not match the rest of the colors in the image n

l Black eyedropper: This allows you to sample the value to be used for black pixels directly

from the image Using the Eyedropper tool sets the value of the black slider to the level of

FIGURE 13.31

Using the Curves Adjustment tool, you can adjust the levels of color channels to change the color

compo-sition and bring detail back to images

Presets Color channel Input tonal range

Curve

Output tonal range Points Curve option Draw Freehand Curve option Smooth Curve option

On-image adjustment tool

Black eyedropper Gray eyedropper White eyedropper

Input range sliders

l White eyedropper: This allows you to sample the value to be used for white pixels

directly from the image Using the Eyedropper tool sets the value of the white slider to the level of the selected pixel

l Gray eyedropper: This allows you to sample the value of a gray pixel directly from the

image The value of the gray pixel is used to calculate the balance of the color channels since a gray pixel of any level should have an equal amount of red, green, and blue

l Auto: Clicking the Auto button applies the Auto Curves Adjustment to the image A later

section in this chapter discusses setting the options for the Auto Curves Adjustment

l Output Tonal Range: This displays the input levels range used by the vertical values of

the curve

l Input Tonal Range: This displays the input levels range used by the horizontal values of

the curve

Note

The Input and Output Tonal Ranges for CYMK are the opposite of those for RGB—in other words, light to dark

instead of dark to light This is because the CYMK color model is subtractive instead of additive n

l Input Range Sliders: These sliders allow you to set the minimum and maximum input

values for distribution of curves in the results from the curves adjustments Adjusting the sliders limits the input range of the curve

l Points Curve option: When this option is selected, the curve is adjusted using control

points Points are added by clicking points the curve To change the curve, drag one of the points on the curve as shown in Figure 13.32 You can add up to 14 points to the curve to get really specific with the tonal adjustments to the image

FIGURE 13.32

Using the Points Curve option, points are added to the image by clicking the curve and the curve can be adjusted by dragging the points

l On-image Adjustment tool: When this option is selected, the mouse curser changes to an

eyedropper As you move the mouse over the image, a circle icon hovers over the curve at

the level value of the pixel under the mouse When you select a pixel in the image, a point

is added to the curve at the level value of the selected pixel You can then change the Output value of the curve at that point by dragging the mouse up and down This option

is available only when the Points Curve option is selected

l Draw Freehand Curve option: When this option is selected, the curve is changed by

drawing freehand on the image as shown in Figure 13.33 The areas of the curve corre-sponding to the line drawn by the Freehand tool are removed from the curve line and the Freehand Output values are used By drawing freehand, you can more accurately change the Output values of specific Input levels, giving the Curves tool lots of power, just as the freehand lines in Figure 13.33 specifically alter the output levels for the input ranges they are drawn over

FIGURE 13.33

Using the Draw Freehand Curve option, you can draw directly on the Curves tool to set the Output values for specific input levels

l Smooth Curve option: Each time you click the Smooth Curve option, the curve is

smoothed a bit until it eventually becomes the original diagonal linear curve This allows you to reduce the variation between the levels This option is extremely useful in joining areas of the curve that are not connected after you use the Draw Freehand Curve tool, as shown in Figure 13.34 This option is available only when the Draw Freehand Curve option is selected

FIGURE 13.34

Using the Smooth Curves option connects areas of the curve that are not connected when the Freehand tool is used and smoothes the curve out, reducing the variation in Output levels

Configuring the Curves Display tool

You can configure several options that change the appearance of the Curves Display tool To con-figure the display options for the Curves tool, click the Curve Display options at the bottom of the Non-adjustment Layer tool or in the Adjustments panel menu to launch the Curves Display Options dialog box, shown in Figure 13.35 In the Curves Display Options dialog box, you can set the following options:

l Light: When the light option is selected, the histogram shown in the Curves tool is based

on the light levels

l Pigment/Ink: When the Pigment/Ink % option is selected, the histogram shown in the

Curves tool is based on the actual pigment used to generate the output image

l Channel Overlays: When this option is selected, the curves for all individual channels are

displayed in their respective colors This option is very useful if you are making curves adjustments to more than one color channel

l Histogram: When this option is selected, the histogram of the selected channel is

dis-played in the background of the Curve view You likely want to keep this option selected

so you can see the distribution of levels as you adjust the curve

l Baseline: When this option is selected, the baseline curve (diagonal line) is displayed so

you can gauge how big of a deviation you are making with the Curve adjustment

l Intersection Line: When this option is selected, intersecting lines are displayed so you

can make more precise adjustments

l Grid size: The two grid size buttons allow you to switch between large and small grids

Smaller grids make the view a bit more confusing but allow you to be a bit more precise

FIGURE 13.35

Adjusting the display options for the Curves Adjustment tool in Photoshop

Configuring the Auto Curves Adjustment

For many general images, the Auto Curves Adjustment in Photoshop is sufficient to correct the lev-els problems in your images To use the Auto Curves Adjustment option, click the Auto button on the Curves Adjustment tool The Auto Curves Adjustment uses the same options as the Auto Levels Adjustment discussed earlier in this chapter

Adjusting the curve to correct color and contrast in images

Adjusting the curves in an image can help fix severe contrast problems, restore detail to images, and remove color problems The following example takes you through the process of using the Curves Adjustment tool to adjust the color levels in a photo:

The photo is completely washed out because of overexposure

Adjustments panel shown in Figure 13.37.

layer to the image and open the Curves tool.

FIGURE 13.36

The detail in this image is extremely limited due to the fact that it was overexposed

Also, the huge shadow on the rock presents a big problem for contrast

FIGURE 13.37

Selecting the Curves tool from the Adjustments panel in Photoshop adds an adjustment layer to the image and launches the Curves Adjustment tool

4 Select the RGB channel, and adjust the black slider to the left edge of the histogram

mountain and the white slider to the right edge of the histogram mountain, as shown in Figure 13.38, to drop the lower level values that are not contributing to the image anyway.

Notice how the image immediately gets additional detail.

FIGURE 13.38

Adjusting the white slider to the edge of the histogram immediately gives you additional detail in the image

it up a bit so the image is not so dark.

Notice that the image lightens a bit, and you actually lose a bit of detail on the upper lev-els, as shown in Figure 13.39

get some of the detail back in the midtones

You kept the detail in the lower levels, but you still added some detail back in the middle levels, as shown in Figure 13.40

FIGURE 13.39

Adding a point to the curve lets you adjust the levels up a bit to gain some detail in the lower levels, but you lose detail in the upper levels

FIGURE 13.40

Adding another point to the curve lets you adjust the middle levels down a bit to gain some detail, but you still lack detail in the upper levels

some of the detail back in the upper tones

You kept most of the detail in the lower and middle levels, but you added some detail back in the upper levels, as shown in Figure 13.41

FIGURE 13.41

Adding another point to the curve lets you adjust the upper levels up a bit to gain some detail in the upper levels without affecting the lower levels

Notice that adjusting the three points slightly adds some detail in areas, as shown in Figure 13.42 You may need to add more points to fix specific level ranges The more you play with the points in the curve, the better you’ll understand the curve adjustment You can always remove points from the curve by dragging them out of the curve window

FIGURE 13.42

Adjusting the points adds even a bit more detail to the image

On the Web Site

The project used to create the image shown in Figure 13.42 can be found on this book’s Web site as

Figure13-42.psd Check out the file on the Web site to really see the color and lighting changes in effect You

can use the Curves Adjustment layer to play around with the Curves tool and see the effect of adding and

adjusting points n

Using the Match Color Tool to Change Colors

The Color Match tool, shown in Figure 13.43, can use the color composition of one image to auto-matically adjust the color composition of another This helps the images match much more closely when placed side by side

One of the best options when you need to color correct several photos from the same shoot is the Color Match tool For example, when you are color correcting a set of photos that are washed out a bit from UV interference, you see a large change when you adjust the hue and saturation to bring back the color As you work with more images your eyes adjust more to the color corrected images and you tend to overcorrect more The result is that the final images don’t match the initial images

FIGURE 13.43

The Color Match tool provides several options to control how colors are adjusted in a target image by

using the colors in a source image