Sử dụng photoshop cs5 part 37 ppt

ptg 222 Chapter 13 Correcting the color using Curves By using a Curves adjustment layer, you can adjust the values in a narrow tonal range, such as the high- lights, quarter tones, midtones, three-quarter tones, or shadows. Precise corrections can be applied to the composite channel (all the channels in the image combined) or to individual color channels. In these steps, you will make tonal corrections rst, then adjust the color. To correct color and tonal values using a Curves adjustment layer: Part 1: Apply tonal adjustments 1. Open an RGB image that needs a color adjustment. A 2. On the Adjustments panel, click the Curves button. Choose Curves Display Options from the Adjustments panel menu, check all four of the Show options (described in the sidebar at right), leave Show Amount Of on the default setting of Light (0-255), then click OK. 3. If the contrast in the image needs improvement, do either of the following: e Input sliders aect the lightest and dark- est tonal values in the image. To increase the contrast (darken the shadows and brighten the highlights), drag the black shadow Input slider and white highlight Input slider inward so they align with the ends of the histogram. e steeper the curve, the greater the contrast. To increase the contrast by establishing the light- est and darkest values in a high-contrast display of clipping called  r e s h o l d mode, Alt-drag/ Option-drag the black slider until a few areas of black appear, and the white slider until a mere smidgen of white appears. (Note that this can also be done in Levels.) 4. For more targeted adjustments, do any of the following: Drag part of the curve; a point will appear on it. For example, to lighten the midtones, drag the middle of the curve upward, or to darken the midtones, drag the middle of the curve downward. ➤ When a tonal value is lightened, its Output value (after adjustment) becomes higher than its Input value (the original brightness value). When a tonal value is darkened, its Output value becomes lower than its Input value. A  i s i m a g e i s u n d e r e x p o s e d ( t o o d a r k ) a n d h a s a b l u e c a s t . USING THE DISPLAY OPTIONS IN CURVES The four Show options in the Curves Display Options dialog are as follows: Channel Overlays Color channel curves Histogram Static histogram for the image Baseline Straight diagonal line representing no adjustments, for comparison Intersection Line Axis guides that appear as you move a point on the curve In the same dialog, you can click the larger grid button to display quarter-tone grid lines or the smaller grid button for a fi ner grid. ptg Adjustments in Depth 223 Click the Targeted Adjustment tool on the panel, then move the pointer over the image; a small circle appears on the curve. Drag upward in the image to lighten the tonal value under the pointer, or downward to darken it. A point corre- sponding to that value appears on the curve. A–B To cycle through the points on the curve, press the + (plus) key. To nudge a selected point, press an arrow key. (To remove a selected point, press Backspace/ Delete.) Keep the Curves controls showing on the panel. To correct the color, follow the steps on the next page. B To lighten the midtones, we clicked the Targeted Adjustment tool, then dragged upward slightly on the grass. Although our adjustments improved the tonal balance, the image still has a blue color cast. We’ll work on that next. Midtones A To lighten the highlights, we moved the white slider to the left. Shadows Highlights ptg 224 Chapter 13 Part 2: Correct the color 1. With the Curves adjustment layer still selected, from the second menu, choose Red to adjust that channel separately, then do any of the following: Drag the middle of the curve upward to add red to the midtones or downward to subtract red (to a lesser extent, this adjustment will also aect the reds in the shadows and highlights). is midtone adjustment is often all that’s required. You can also add or subtract red in the shadows by dragging the lower part of the curve, or in the highlights by dragging the upper part of the curve. A Click the Targeted Adjustment tool on the panel, then drag in the image to adjust the part of the curve that corresponds to that color value. B 2. Choose the Green channel, then the Blue channel, adding or subtracting that color from the image, as in the preceding step. You can switch back and forth between the color chan- nels, and readjust them if needed ( A–D , next page). 3. Optional: To lessen the impact of the Curves adjustment layer, lower the layer opacity; or click the adjustment layer mask, then with the Brush tool and the Foreground color set to black, apply brush strokes to the image. ➤ To save your adjustment settings as a preset for future use, see page 200. APPLYING CURVES TO A CMYK IMAGE The Curves options work the opposite way for a CMYK image than for an RGB image: ➤ Readouts from the Curves graph refer to percentages of ink. Black equals 100% and white equals 0%. ➤ Shadow values are represented by the upper right part of the curve, and highlights are represented by the lower left part of the curve. Drag the curve down- ward to lighten a tonal value or upward to darken it. For an individual color channel, you can drag the curve upward to add more of that color or downward to subtract it. ➤ Colors work in tandem. For example, reducing cyan adds red, reducing magenta adds green, and reducing yellow adds blue. B With the Targeted Adjustment tool, we dragged slightly upward in the gray area of the clouds. is produced a point on the curve (right) and added some red to the clouds and other midtones. A To add red to the highlight areas (such as in the clouds), with the Red channel selected, we moved the white slider slightly inward. ptg Adjustments in Depth 225 D To reduce blue in the midtones, we dragged downward slightly with the Targeted Adjustment tool on the road. A point appeared on the curve. is is the cumulative result of all our Curves adjustments. C And nally, to remove green from the highlights, with the Blue channel selected, we dragged the white slider slightly inward. A To remove red and blue from the high- lights, with the Green channel selected, we dragged the white slider slightly inward. B To reduce green in the image, we dragged downward with the Targeted Adjustment tool on the gray clouds and on the grass below the barn. Two points appeared on the curve. ptg 226 Chapter 13 A We corrected a photo via a Levels adjustment layer, then saved our settings as a preset. B We clicked the tab for another photo in the same series, created a Levels adjustment layer, then chose our preset of saved settings from the preset menu. Open a series of photos that were shot under the same lighting conditions, have the same color profi le, and require the same color correction. Adjust one photo via a Levels, Curves, Exposure, Hue/Saturation, Black & White, Channel Mixer, or Selective Color adjustment layer, then save your settings as a preset via the Save [preset name] Preset command on the panel menu. A Click another document tab, then for the same type of adjustment layer, choose your saved preset from the preset menu. B Note: To copy adjustment settings for controls that can’t be saved as a preset, on the Arrange Documents menu on the Application bar, click an appropriate “Up” button to tile the documents. Drag and drop the adjustment layer from the Layers panel of the corrected document into each of the other document windows. APPLYING THE SAME ADJUSTMENT SETTINGS TO MULTIPLE IMAGES . the lower part of the curve, or in the highlights by dragging the upper part of the curve. A Click the Targeted Adjustment tool on the panel, then drag in the image to adjust the part of the. equals 0%. ➤ Shadow values are represented by the upper right part of the curve, and highlights are represented by the lower left part of the curve. Drag the curve down- ward to lighten a tonal. highlights, we moved the white slider to the left. Shadows Highlights ptg 224 Chapter 13 Part 2: Correct the color 1. With the Curves adjustment layer still selected, from the second menu,