Photoshop cs5 cho nhiếp ảnh gia part 53 pot

Blue channel Figure 8.19 Looking at the Red, Green, and Blue channels, it’s clear that the Blue channel offers the most contrast between the sky and the flower... make a copy of the cha

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For Photoshop Elements Users: Other Ways of Merging Images (Continued)

P hoto by J osh A non

and practice combining them

Combining Elements from Multiple Pictures

When you start combining elements from various pictures, you begin to be more

cre-ative with your images ethically, it’s important to acknowledge that what you’re

pre-senting is not a documentary photograph but rather a photo illustration or photo art

that doesn’t make it inherently more or less valuable than a straight photograph—

just different often, a photo illustration can convey the essence or spirit of a place

better than a single straight photograph But creating something that didn’t exist and

claiming it is not a manipulated photograph creates trouble for all photographers

the image in Figure 8.17 has impact, but it’s a composite and needs to be presented

as such

it’s essential to make good selections when creating composites We’ll cover some advanced selection techniques here and then show you how to put your

selec-tions to work to create a variety of composites

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Figure 8.17 Images like this can often be confused with “lucky” shots and ethically must be presented as composites.

Advanced Selection Methods

Chapter 4, “Foundations,” covered some of the basic selection tools, but when you make composites, sometimes you need more sophisticated means of making selections

Different techniques work most effectively with different images, so it pays to under-stand several approaches

if you know ahead of time that you’re likely to want to use one part of a picture

as a composite, it’s a good idea to try to photograph it so that it contrasts as much as possible with the background that makes it easier to select, no matter which tech-nique you choose

Creating a Selection within a Channel

this sounds a lot more difficult than it is, but don’t let the sound of it intimidate you

Recall that your images have pixel information in three channels: a Red channel, a Blue channel, and a Green channel You access these channels by clicking the Channels panel,

as shown in Figure 8.18 By default, Channels shares a panel window with Layers

Figure 8.18 To access the individual

channels, click the Channels panel

sometimes it’s easier to make a selection using one of the three color channels rather than the RGB image itself this is the case when there is good contrast within

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a particular channel For example, making a selection of a sky based on a channel is

quite useful when the sky meets trees and vegetation with many fine branches

We’ll demonstrate this approach to select the sky in this poppy image:

1. Choose Channels, and then click each of the three channels, one at a time, to

determine which has the best contrast in the area of interest With the poppy picture, clearly the Blue channel offers the best contrast to separate the sky and the flower, as you can see in Figure 8.19

Blue channel

Figure 8.19 Looking at the Red,

Green, and Blue channels, it’s clear that the Blue channel offers the most contrast between the sky and the flower

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2. make a copy of the channel offering the most contrast—in this case, the Blue channel—by dragging that channel layer to the new Channel icon at the bottom of the Channels panel

3. maximize the contrast between the area you want to select and the rest of the image by choosing image > Adjustments > Levels this is one of the few times you make changes directly on the pixels because there is no way to create an adjustment layer for a channel Drag in the black point and white point slid-ers to turn the preview nearly black and white, as illustrated in Figure 8.20 A small transition area of gray is actually beneficial

Figure 8.20 Use the sliders in the Levels dialog box to turn this channel into black and white.

4. to fine-tune the selection, you’ll most likely need to use the Brush tool and paint some areas with black and some areas with white

5. once you have a black-and-white preview created (which is actually a mask), click the Load Channel as selection icon at the bottom of the Channels panel this creates a selection based on the mask you just created the white areas are selected

6. You can invert the selection (by choosing select > inverse on the main menu) if you find that you have selected the opposite part of the image

7. After going through all this to make a selection, it’s a good idea to save the selection by choosing select > save and naming it (see Figure 8.21) that way, you can refer to it in the future

Figure 8.21 After making a timeconsuming selection, it’s a good

idea to save the selection

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For Photoshop Elements Users: Extracting an Object from Its Background

Although Photoshop CS5 does not have an Extraction filter, Elements has the Magic Extractor To use it, follow these steps:

to extract Zoom in and move around using the Zoom and Hand buttons, and adjust Brush

any bad points

object

Katrin Eismann (New Riders, 2004)

2. make a copy of the channel offering the most contrast—in this case, the Blue

channel—by dragging that channel layer to the new Channel icon at the

bottom of the Channels panel

3. maximize the contrast between the area you want to select and the rest of the

image by choosing image > Adjustments > Levels this is one of the few times

you make changes directly on the pixels because there is no way to create an

adjustment layer for a channel Drag in the black point and white point

slid-ers to turn the preview nearly black and white, as illustrated in Figure 8.20 A

small transition area of gray is actually beneficial

Figure 8.20 Use the sliders in the Levels dialog box to turn this channel into black and white.

4. to fine-tune the selection, you’ll most likely need to use the Brush tool and

paint some areas with black and some areas with white

5. once you have a black-and-white preview created (which is actually a mask),

click the Load Channel as selection icon at the bottom of the Channels

panel this creates a selection based on the mask you just created the white

areas are selected

6. You can invert the selection (by choosing select > inverse on the main menu) if

you find that you have selected the opposite part of the image

7. After going through all this to make a selection, it’s a good idea to save the

selection by choosing select > save and naming it (see Figure 8.21) that way,

you can refer to it in the future

Figure 8.21 After making a timeconsuming selection, it’s a good

idea to save the selection

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For Photoshop Elements Users: Creating a Selection within a Channel

Although Elements does not have a Channels panel, we can fake this selection method by con

verting our image to black and white

Layer

value of 100 for Red and 0 for Green and Blue to let you just see the Red channel) The sidebar “For Elements Users: Matching Exposures” earlier in this chapter shows what selecting just the Red channel looks like

instructions

select the part of the image you wish to be selected

selection from Step 7

If you plan to use your selection in a layer mask, replace Steps 7–9 as follows:

Compositing the Elements

perhaps you have several images, each containing elements that you would like to combine into a single image often, the relative sizes of the various elements need to

be modified—you can take care of that during the process of compositing the ele-ments in the next example, we’ll create a composite of some birds, a background, and

a moon:

1. open your destination photo (the photo that you are going to use as the main photo), set its resolution to 300 dpi (or your preferred printing resolution) by choosing image > image size, and uncheck the Resample image option You don’t want to interpolate the file now; just set it to the same resolution see Fig-ure 8.22 for our destination photo