Sử dụng photoshop cs5 part 49 pdf

In this chap-ter, you’ll apply the Lens Blur filter and use vignettes to create a focal point in a photo; apply the Lens Correction filter to correct for camera lens distor-tion; apply t

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

to orchestrate a scene, such as

blur-riness to convey motion or a shallow

depth of field to contrast an in-focus

subject with its background In Photoshop,

you can apply similar special effects, and also correct

for defects produced by a camera lens In this

chap-ter, you’ll apply the Lens Blur filter and use vignettes

to create a focal point in a photo; apply the Lens

Correction filter to correct for camera lens

distor-tion; apply the Motion Blur filter to simulate modistor-tion;

and use the Sharpen tool and the Smart Sharpen and

Unsharp Mask filters 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 field 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 field — either in

front of it or behind it — will be blurred Other

fac-tors affecting the focus are the zoom setting and the

camera lens

The Lens Blur filter 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 filter All of this

number crunching does have a price, however: The

filter 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 The Lens Blur filter

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

Click the layer thumbnail, then choose Filter >

Blur > Lens Blur The Lens Blur dialog opens A

4 Check Preview and click a speed For a large

file (larger than 100 MB), click Faster, or for a

smaller file, 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 field 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 The 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 effect

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.

6 In the Iris area, use the Radius value to

con-trol the intensity of the blur This produces

the most pronounced effect of all the controls

in the dialog (The 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 Threshold slider (slightly) to

con-trol which tonal range the Brightness setting affects At 255, only pure white pixels will be affected, whereas at a low setting, most of the blurred areas will be brightened

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 specified that a layer mask be used by the Lens Blur filter 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) The dialog settings we chose are shown in

the figure on the preceding page.

A In the original image, all the areas are in focus

D Our Smart Object layer (Layer 1), with its filter 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 filter mask An advantage of this method

is that you can modify the filter 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 Refine 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.

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 Difference 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.

Applying the Lens Correction filter

The Lens Correction filter 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) The CS5 version of this filter offers many

enhancements, such as the ability to correct for

idiosyncrasies of a specific 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 profile, right-click the

Lens Profile 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

fix pincushion distortion), or raise this value to

pinch the image inward (to fix 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 off 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 fill 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 The 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

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.