Sử dụng photoshop cs5 part 49 pdf

ptg refocusing IN THIS CHAPTER Applying the Lens Blur fi lter . . . . . . .287 Changing the focus with a vignette . .290 Applying the Lens Correction fi lter . .292 Applying the Motion Blur fi lter . . . . .294 Using the Sharpen tool . . . . . . . . . .295 Applying the Smart Sharpen fi lter . . .296 Applying the Unsharp Mask fi lter . . . .299 17 Photographers use focusing techniques to orchestrate a scene, such as blur- riness to convey motion or a shallow depth of eld to contrast an in-focus subject with its background. In Photoshop, you can apply similar special eects, and also correct for defects produced by a camera lens. In this chap- ter, you’ll apply the Lens Blur lter and use vignettes to create a focal point in a photo; apply the Lens Correction lter to correct for camera lens distor- tion; apply the Motion Blur lter to simulate motion; and use the Sharpen tool and the Smart Sharpen and Unsharp Mask lters to resharpen the image. Applying the Lens Blur filter In a photograph, some parts of the scene are more in focus than others. If your camera lets you adjust the depth of eld via the aperture, or f-stop setting (it’s not a “point-and-shoot” type of camera), you can con- trol how much of your subject matter stays in focus. Objects that are outside the depth of eld — either in front of it or behind it — will be blurred. Other fac- tors aecting the focus are the zoom setting and the camera lens. e Lens Blur lter in Photoshop attempts to repli- cate this type of blurring. What formerly required the use of multiple channels, gradients, and editing steps can now be accomplished with a single lter. All of this number crunching does have a price, however: e lter may process slowly on a large image. To apply the Lens Blur filter: 1. Click an image layer (or duplicate the Background via Ctrl-J/Cmd-J), then click the Add Layer Mask button on the Layers panel. 2. Keep the layer mask thumbnail selected. Choose the Gradient tool (G or Shift-G), click the Gradient picker arrowhead on the Options bar, and click the “Black, White” preset. Shift-drag across the entire document window vertically or hori- zontally to apply the gradient. e Lens Blur lter is going to use this gradient “invisibly.” Keep this in mind when you choose a Blur Focal Distance setting in step 5. (Don’t concern yourself with where the white and black areas of the gradient land; you’ll be able to swap them in the Lens Blur dialog.) 3. Shift-click the layer mask thumbnail to disable the layer mask (you don’t want to mask the imagery). Continued on the following page ptg 288 Chapter 17 Click the layer thumbnail, then choose Filter > Blur > Lens Blur. e Lens Blur dialog opens. A 4. Check Preview and click a speed. For a large le (larger than 100 MB), click Faster, or for a smaller le, click More Accurate. You can also change the zoom level for the preview via the zoom buttons or menu in the lower left corner of the preview window. We like to use the Fit in View setting. 5. To mimic the depth of eld in a camera, you will specify that the grayscale values in the layer mask control where the blur is applied. In the Depth Map area, do the following: From the Source menu, choose Layer Mask as the source for the depth map. e grayscale values in the source will control which areas remain in focus. (A setting of None would allow the whole image to blur uniformly.) To set the Blur Focal Distance, either specify which grayscale value (from 0, black, to 255, white) in your depth map will remain in full focus via the scrubby slider or, in the preview, click the area that you want to keep in focus. In either case, you are choosing a grayscale value from the gradient in the layer mask. Shades lighter or darker than this value will become progressively more blurry. You’ll see the eect of this after moving the Radius slider, in the next step. Optional: Check Invert to swap the white and black areas in the depth map, and thereby swap the areas in focus with those that are not. A After Shift-dragging upward in the document with the Gradient tool (starting from the bottom of the image), we opened the Lens Blur dialog. ptg Refocusing 289 6. In the Iris area, use the Radius value to con- trol the intensity of the blur. is produces the most pronounced eect of all the controls in the dialog. (e other Iris sliders are used for creating “photographic” highlights.) Keep the Shape setting on the default setting of Hexagon (6). ➤ At any time while choosing settings, you can uncheck, then recheck Preview to compare the original and blurred images. 7. Blurring averages the values of neighboring pixels and tends to gray out white specular highlights. In the Specular Highlights area, you can use the Brightness slider to brighten highlight areas that have become blurred and move the  r e s h o l d slider (slightly) to con- trol which tonal range the Brightness setting aects. At 255, only pure white pixels will be aected, whereas at a low setting, most of the blurred areas will be brightened. 8. Optional: If the blurring smoothed out too much noise from the original photo, you can reintroduce noise by doing any of the following: Move the Noise: Amount slider slightly, click Distribution: Uniform or Gaussian, or check Monochromatic to limit the noise to just gray- scale pixels instead of color pixels. 9. Click OK. A–B A In the original photo, both the foreground and background areas are in focus. Light grayscale values are allowing full blurring in this area of the photo. Because we chose a dark grayscale value (47) as the Blur Focal Distance, no blurring is occurring in this area of the photo. Intermediate grayscale values are allowing par- tial blurring of this area of the photo. B We specied that a layer mask be used by the Lens Blur lter to blur the background of this photo, in order to draw the viewer’s attention to the foreground (a detail of the mask is shown at right above). e dialog settings we chose are shown in the gure on the preceding page. ptg 290 Chapter 17 A In the original image, all the areas are in focus. D Our Smart Object layer (Layer 1), with its lter mask and Smart Filter, are shown in this Layers panel. Changing the focus with a vignette Next, you’ll create an area of focus by using a Smart Filter and lter mask. An advantage of this method is that you can modify the lter settings and edit the mask to change which part of the image is in focus. To create an area of focus (a vignette) by using a mask: 1. Open an image in which you want to emphasize the center. A 2. On the Layers panel, click an image layer or the Back ground, then press Ctrl-J/Cmd-J to duplicate it. 3. Select the area of the image that you want to emphasize (keep in focus). For example, you could use the Elliptical Marquee tool (M or Shift-M) then Alt-drag/Option-drag to create an oval (as we did), or use the Lasso tool to create an irregular-shaped selection. 4. On the Options bar, click Refine Edge. From the View menu, choose On White (W), ★ increase the Feather value to soften the selection edge, then click OK. 5. Press Ctrl-Shift-I/Cmd-Shift-I (Select > Inverse) to swap the selected and unselected areas. B 6. Choose Filter > Convert for Smart Filters, then click OK if an alert dialog appears. 7. Choose Filter > Blur > Gaussian Blur. In the Gaussian Blur dialog, click the zoom out (–) button until you see all or most of the image in the preview window, increase the Radius for the desired amount of blurring, then click OK. C–D ➤ To change the Radius setting at any time, double-click the Gaussian Blur listing on the Layers panel. C For our vignette, we chose a Radius value of 5.7 pixels in the Gaussian Blur dialog. B We created an oval selection, used Rene Edge to feather it (a Feather value of 40 px for this 300 ppi photo), and chose Select > Inverse. Now the areas out- side the oval marquee are selected. ptg Refocusing 291 Another way to create a vignette is by manipulating light and dark values. Here you will use (and move) the layer mask on a Levels adjustment layer to control where the vignette is positioned in the image. To create a darkening vignette via Levels: 1. Open an image in which you want to emphasize an area at or near the center. 2. Follow steps 2–4 on the preceding page, and keep the duplicate layer selected. 3. On the Adjustments panel, click the Levels button. Ignore the Levels settings for the moment. 4. With the adjustment layer thumbnail selected, press Ctrl-I/Cmd-I to invert the mask. 5. On the Adjustments panel, move the white Output Levels slider to the left to darken all but the masked part of the image. A 6. Optional: To change the location of the darken- ing vignette, on the Layers panel, click the Levels adjustment layer, click the Link Layer Mask icon to unlink the mask from the adjustment layer, click the layer mask thumbnail, then with the Move tool (V), drag the mask shape to the desired location in the document window — it’s like shining a spotlight. B–D On the Layers panel, click again to restore the link icon. A We darkened the image via a Levels adjustment layer (we moved the white Output Levels slider to 180). D As an optional variation to make the lighting more dra- matic, we changed the blending mode of the Levels adjust- ment layer to Dierence and lowered its opacity to 80%. C Because we moved the layer mask to the lower left, the light area (the area blocked by the mask) is now on that side. B We unlinked the layer mask from the adjustment layer thumbnail (the link icon disappeared), then with the Move tool, moved the layer mask to the left. ptg 292 Chapter 17 Applying the Lens Correction filter e Lens Correction lter lets you correct for many types of lens distortion, such as a building or column that tilts away from the camera (called “keystoning”), color fringes along high-contrast edges (chromatic aberration), or under- or overexposure at the edges (vignetting). e CS5 version of this lter oers many enhancements, such as the ability to correct for idiosyncrasies of a specic camera model and lens. To correct lens distortion: ★ 1. Open an RGB photo ( A , next page). On the Layers panel, click an image layer or the Back- ground, then press Ctrl-J/Cmd-J to duplicate it. 2. Right-click the duplicate layer and choose Convert to Smart Object. 3. Choose Filter > Lens Correction (Ctrl-Shift-R/ Cmd-Shift-R). At the bottom of the dialog, check Preview and uncheck Show Grid. 4. To try an automatic correction, in the Auto Correction tab, from the menus under Search Criteria, choose your Camera Make and Camera Model; or if your model isn’t listed, choose All. From the Lens Model menu, choose All, then under Lens Profiles, click the nearest match to your camera lens ( B , next page). To further customize the prole, right-click the Lens Prole that you have chosen and pick a camera setting, such as “28mm, f/4.5, 1 m.” Note that if this data is in the camera’s EXIF meta- data, the correct setting is chosen automatically. 5. Under Correction, check which problem in the photo needs correction: Geometric Distortion, Chromatic Aberration, or Vignette. 6. If the automatic correction wasn’t fully success- ful, click the Custom tab, then do one of the following, depending on what needs correction: Under Geometric Distortion, lower the Remove Distortion value to spread the image out (to x pincushion distortion), or raise this value to pinch the image inward (to x barrel distortion). Use the Chromatic Aberration sliders to correct any color fringes along high-contrast edges (the Fix Green/Magenta Fringe slider is new). Use the Vignette sliders to help correct for under- or overexposure at the edges of the image. 7. To evaulate the correction of geometric distor- tion relative to a grid, check Show Grid (located below the preview window). You can change the grid size via the Size slider or change the grid color by clicking the Color swatch. 8. To further correct geometric distortion, under Transform, do any of the following: Lower the Vertical Perspective value to widen the top of the image ( C , next page), or raise it to widen the bottom. After doing this, you may need to readjust the Remove Distortion value to level the horizontal shapes. Lower the Horizontal Perspective value to widen the left edge of the image, or raise it to widen the right edge of the image. To rotate the image, change the Angle via the scrubby slider (it’s easier to control than the dial). ➤ Press P to toggle the preview o and on. 9. To control how areas at the edges of the image are treated as a result of a distortion correction, do any of the following: In the Auto Correction tab, check Auto Scale Image, then from the Edge menu, choose to have the empty areas ll with an Edge Extension (extension of the image), Transparency, Black Color, or White Color. In the Custom tab, increase the Scale value. Crop the image after exiting the dialog. 10. Optional: To save all the current settings as a preset, from the Manage Settings menu in the Custom tab, choose Save Settings, enter a name (keep the .lcs extension and default loca- tion), then click Save. e preset can now be chosen from the Settings menu for any image. Or if you prefer to save all the settings except the Transform settings as a preset for photos that contain camera EXIF metadata, choose Set Lens Default from the Manage Settings menu. 11. Click OK ( D , next page). ➤ To change the Lens Correction settings at any time, double-click the Smart Filter listing on the Layers panel. ➤ From the Settings menu in the Custom tab, you can choose Previous Correction to apply the last- used settings or Default Correction to restore the default values to all the options. ptg Refocusing 293 C To widen the top of the photo, we clicked the Custom tab, then reduced the Vertical Perspective value (under Transform). A In the original photo, the towers are leaning too far inward. B We chose these options in the Auto Correction tab of the Lens Correction dialog, but they pro- duced only a minor correction. D As a result of the Lens Correction adjust- ments, now the towers look more vertical. . convey motion or a shallow depth of eld to contrast an in-focus subject with its background. In Photoshop, you can apply similar special eects, and also correct for defects produced by a camera. lters to resharpen the image. Applying the Lens Blur filter In a photograph, some parts of the scene are more in focus than others. If your camera lets you adjust the depth of. fac- tors aecting the focus are the zoom setting and the camera lens. e Lens Blur lter in Photoshop attempts to repli- cate this type of blurring. What formerly required the use of multiple