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Extracting objects from their background (Photoshop)
The Extract command provides a sophisticated way to isolate a foreground object and
erase its background on a layer. Even objects with wispy, intricate, or undefinable edges
may be clipped from their backgrounds with a minimum of manual work.
Note: For simpler cases, you can instead use the background eraser tool.
To extract an object, you use tools in the Extract dialog box. First you draw a highlight that
marks the edges of the object, and define the object’s interior. Then you can preview the
extraction and redo it or touch up the result as needed. When you extract the object,
Photoshop erases its background to transparency. Pixels on the edge of the object lose
their color components derived from the background, so they can blend with a new
background without producing a color halo.
You can add back opacity to the background and create other effects by using the
Edit > Fade command after an extraction. (See “
B
lending fi
lt
er eff
ec
ts (P
hot
oshop)
”
on
page
322
.)
To extract an object from its background:
1 In the Layers palette, select the layer containing the object you want to extract. If you
select a background layer, it becomes a normal layer after the extraction.
To avoid losing the original image information, duplicate the layer or make a snapshot of
the original image state.
Note: If the layer contains a selection, the extraction erases the background only in the
selected area.
2 Choose Filter > Extract.
You use tools in the Extract dialog box to specify which part of the image to extract.
You can resize the dialog box by dragging its lower right corner.
3 Specify options for tools in the dialog box (you can change these settings at any time):
•
For Brush Size, enter a value, or drag the slider to specify the width of the edge
highlighter, eraser, cleanup, and edge touchup tools.
•
For Highlight, choose a preset color option, or choose Other to specify a custom color
for the highlight.
•
For Fill, choose a preset color option, or choose Other to specify a custom color for the
area covered by the fill tool.
•
If you are highlighting a well-defined edge, select Smart Highlighting. This option helps
you keep the highlight on the edge, and applies a highlight that is just wide enough to
cover the edge, regardless of the current brush size.
4 Adjust the view as needed:
•
To magnify an area, select the zoom tool in the dialog box, and click in the preview
image. To zoom out, hold down Alt (Windows) or Option (Mac OS) as you click.
•
To view a different area, select the hand tool in the dialog box, and drag in the preview
image.
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5 Define the edge of the object you want to extract:
•
To draw a highlight that marks the edge, select the edge highlighter tool in the
dialog box, and drag so that the highlight slightly overlaps both the foreground object
and its background. Use Smart Highlighting to trace sharper edges. Use a large brush to
cover wispy, intricate edges where the foreground blends into the background, such as
hair or trees.
If you use Smart Highlighting to mark an object edge that is near another edge,
decrease the brush size if conflicting edges pull the highlight off the object edge.
If the object edge has a uniform color on one side and high-contrast edges on the other
side, keep the object edge within the brush area but center the brush on the uniform
color.
•
If the object has a well-defined interior, make sure that the highlight forms a complete
enclosure. You do not need to highlight areas where the object touches the image
boundaries. If the object lacks a clear interior, highlight the entire object.
•
To base the highlight on a selection saved in an alpha channel, choose the alpha
channel from the Channel menu. The alpha channel should be based on a selection of
the edge boundary. If you modify a highlight based on a channel, the channel name in
the menu changes to Custom.
•
To erase the highlight, select the eraser tool in the dialog box, and drag over the
highlight. To erase the entire highlight, press Alt+Backspace (Windows) or
Option+Delete (Mac OS).
6 Define the foreground area:
•
If the object has a well-defined interior, select the fill tool in the dialog box.
Click inside the object to fill its interior. (Clicking a filled area with the fill tool removes
the fill.)
•
If the object is especially intricate or lacks a clear interior, make sure that the highlight
covers the entire object, and then select Force Foreground. Select the eyedropper tool
in the dialog box, and click inside the object to sample the foreground color, or click
in the Color text box and use a color picker to select the foreground color. This
technique works best with objects that contain tones of a single color.
7 Click Preview to preview the extracted object, or skip to step 10 to extract the object
without a preview.
Selected area highlighted and filled, and extracted object
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Zoom in as needed, and set any preview options:
•
Use Show menu options to switch between previews of the original and extracted
images.
•
Use Display menu options to preview the extracted object against a colored matte
background or as a grayscale mask. To display a transparent background, choose None.
•
Select Show Highlight or Show Fill to display the object’s highlight or fill.
8 If necessary, repeat the extraction to improve the results (when you are finished, you
can perform final touch-ups as described in step 9):
•
To perform another extraction after adjusting the highlight and fill, repeat steps 5, 6,
and 7.
•
To perform another extraction with new extraction settings, change the Smooth, Force
Foreground, or Color settings, and repeat step 7.
Note: To specify the amount of smoothing of the extracted object, drag the Smooth slider
or enter a value. It is usually best to begin with a zero or small value to avoid unwanted
blurring of details. If there are sharp artifacts in the extraction result, you can increase the
Smooth value to help remove them in the next extraction.
9 Touch up the extraction results as needed:
•
To erase background traces in the extracted area, use the cleanup tool . The tool
subtracts opacity and has a cumulative effect. You can also use the cleanup tool to fill
gaps in the extracted object. Hold down Alt (Windows) or Option (Mac OS) while
dragging to add back opacity.
•
To edit the edge of the extracted object, use the edge touchup tool . The tool
sharpens edges and has a cumulative effect. If there is no clear edge, the edge touchup
tool adds opacity to the object or subtracts opacity from the background.
10 Click OK to apply the final extraction. On the layer, all pixels outside the extracted
object are erased to transparency.
Note: For best results in cleaning up stray edges, use the cleanup and edge touchup tools
in the Extract dialog box. You can also clean up after an extraction by using the
background eraser and history brush tools in the toolbox.
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Transforming and Retouching
Changing the size of the work canvas
The Canvas Size command lets you add or remove work space around an existing image.
You can crop an image by decreasing the canvas area. Added canvas appears in the same
color or transparency as the background.
To use the Canvas Size command:
1 Choose Image > Canvas Size.
2 (Photoshop) Choose the units of measurement you want.
3 The Columns option measures width in terms of the columns specified in the Rulers &
Units preferences. For more information, see “
U
sing c
olumns (P
hot
oshop)
”
on page
44
.
4 Do one of the following:
•
Enter the dimensions you want the canvas to be in the Width and Height boxes.
•
Select Relative, and enter the amount by which you want to increase or decrease the
size of the canvas. (Enter a negative number to decrease the size of the canvas.)
5 For Anchor, click a square to indicate where to position the existing image on the new
canvas.
6 Click OK.
Original canvas, and canvas added to top of image
Rotating and flipping entire images
The Rotate Canvas commands let you rotate or flip an entire image. The commands do not
work on individual layers or parts of layers, paths, or selection borders.
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To rotate or flip an entire image:
Choose Image > Rotate Canvas, and choose one of the following commands from the
submenu:
•
180°
to rotate the image by a half-turn.
•
90° CW to rotate the image clockwise by a quarter-turn.
•
90° CCW to rotate the image counterclockwise by a quarter-turn.
•
Arbitrary to rotate the image by the angle you specify. If you choose this option, enter
an angle between –359.99 and 359.99 in the angle text box, and then select CW or CCW
to rotate clockwise or counterclockwise. Click OK.
•
Flip Canvas Horizontal (Photoshop) or Flip Horizontal (ImageReady) to flip the image
horizontally, along the vertical axis.
•
Flip Canvas Vertical (Photoshop) or Flip Vertical (ImageReady) to flip the image verti-
cally, along the horizontal axis.
Cropping images
Cropping is the process of removing portions of an image to create focus or strengthen
the composition. You can crop an image using the crop tool and the Crop command.
You can also trim pixels using the Trim command.
The crop tool provides the most options for cropping images.
To crop an image using the crop tool:
1 Select the crop tool .
2 Set the mode of the crop tool:
•
(Photoshop) To crop the image without resampling (default), make sure that all the text
boxes in the options bar are empty. You can click the Clear button to quickly clear all
text boxes.
•
(Photoshop) To resample the image during cropping, enter a height, width, and/or
resolution in the options bar.
•
(ImageReady) To crop the image without resampling, make sure that Fixed Size is
deselected in the options bar.
•
(ImageReady) To resample the image during cropping, select Fixed Size, and enter a
height and width in the options bar.
•
To resample an image based on the dimensions and resolution of another image,
open the other image, select the crop tool, and click Front Image in the options bar.
(In ImageReady, you must select the Fixed Size option to access the Front Image
button.) Then make the image you want to crop active.
Resampling during cropping combines the function of the Image > Image Size
command with that of the crop tool. (See “
A
b
out r
esampling
”
on page
66
.)
3 Define the cropping marquee by dragging over the part of the image you want to keep.
The marquee doesn’t have to be precise—you can adjust it later.
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4 Do the following in the options bar:
•
Specify whether you want to hide or delete the cropped area. Select Hide to preserve
the cropped area in the image file. You can make the hidden area visible by moving the
image with the move tool. Select Delete to discard the cropped area.
Note: In Photoshop, the Hide option is not available for images that contain only a
background layer. If you want to crop a background by hiding, convert the background to
a regular layer first. (See “
A
b
out the back
gr
ound la
y
er
”
on page
285
.) In ImageReady,
cropping a background by hiding automatically converts the background to a regular
layer.
•
Specify whether you want to use a cropping shield to shade the area of the image that
will be deleted or hidden. When Shield is selected, you can specify a color and opacity
for the cropping shield. When Shield is deselected, the area outside the cropping
marquee is revealed.
5 If necessary, adjust the cropping marquee:
•
To move the marquee to another position, place the pointer inside the bounding box
and drag.
•
To scale the marquee, drag a handle. To constrain the proportions, hold down Shift as
you drag a corner handle.
•
To rotate the marquee, position the pointer outside the bounding box (the pointer
turns into a curved arrow), and drag. To move the center point around which the
marquee rotates, drag the circle at the center of the bounding box.
Note: In Photoshop, you can’t rotate the marquee for an image in Bitmap mode.
6 Do one of the following:
•
Press Enter (Windows) or Return (Mac OS); click the Commit button in the options
bar; or double-click inside the cropping marquee.
•
To cancel the cropping operation, press Esc or click the Cancel button in the
options bar.
To crop an image using the Crop command:
1 Select the part of the image you want to keep. (See “
U
sing the mar
quee t
o
ols
”
on
page
158
.)
2 Choose Image > Crop.
To crop an image using the Trim command:
1 Choose Image > Trim.
2 In the Trim dialog box, select an option:
•
Transparent Pixels to trim away transparency at the edges of the image, leaving the
smallest image containing non-transparent pixels.
•
Top Left Pixel Color to remove an area the color of the upper left pixel from the image.
•
Bottom Right Pixel Color to remove an area the color of the lower right pixel from the
image.
3 Select one or more areas of the image to trim away: Top, Bottom, Left, or Right.
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Transforming perspective while cropping (Photoshop)
The crop tool in Photoshop has an additional option that allows you to transform the
perspective in an image. This is very useful when working with images that contain
keystone distortion. Keystone distortion occurs when an object is photographed from an
angle rather than from a straight-on view. For example, if you take a picture of a a tall
building from ground level, the edges of the building appear closer at the top than they
do at the bottom.
Note: You cannot transform the perspective of 16-bit-per-channel images.
Steps to transform perspective:
A. Draw initial cropping marquee B. Adjust cropping marquee to match the object’s edges
C. Extend the cropping bounds D. Final image
To transform the perspective in an image:
1 Select the crop tool and set the crop mode. (See “
C
r
opping images
”
on page
178
.)
2 Drag the cropping marquee around an object that was rectangular in the original scene
(although it doesn’t appear rectangular in the image). You’ll use the edges of this object to
define the perspective in the image. The marquee doesn’t have to be precise—you’ll
adjust it later.
Important: You must select an object that was rectangular in the original scene or
Photoshop will not be able to transform the perspective in the image.
3 Select Perspective in the options bar, and set the other options as desired.
(See “
C
r
opping images
”
on page
178
.)
4 Move the corner handles of the cropping marquee to match the object’s edges.
This defines the perspective in the image, so it is important to precisely match the
object’s edges.
A
C
D
B
Documents you may be interested
Documents you may be interested
