Clipping paths
Clipping paths
Crop using a graphic’s path or alpha channel
Create a clipping path automatically
Clipping path options
Convert a clipping path to a graphics frame
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Clipping paths
Clipping paths crop part of the artwork so that only a portion of the artwork appears through the shape or shapes you create. You can create clipping paths to hide unwanted parts of an image, creating both a path for the image and a frame for the graphic. By keeping the clipping path and graphics frame separate, you can freely modify the clipping path without affecting the graphics frame by using the Direct Selection tool and other drawing tools in the toolbox.
You can create clipping paths in the following ways:
Place already-saved graphics with paths or alpha (mask) channels, which InDesign can use automatically. You can add paths and alpha channels to graphics using a program such as Adobe Photoshop.
Use the Detect Edges option in the Clipping Path command to generate a clipping path for a graphic that was saved without one.
Use the Pen tool to draw a path in the shape you want, and then use the Paste Into command to paste the graphic into the path.
When you use one of InDesign’s automatic methods to generate a clipping path, the clipping path is attached to the image, resulting in an image that is clipped by the path and cropped by the frame.
Note: The graphics frame displays the color of the layer it appears on, and the clipping path is drawn in the inverse color of the layer. For example, if the layer color is blue, the graphics frame will appear as blue, and the clipping path will appear as orange.
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Crop using a graphic’s path or alpha channel
InDesign can crop an imported EPS, TIFF, or Photoshop graphic using the clipping path or alpha channel saved with the file. When an imported graphic includes more than one path or alpha channel, you can choose which path or alpha channel to use for the clipping path.
An alpha channel is an invisible channel that defines transparent areas of a graphic. It’s stored inside a graphic with the RGB or CMYK channels.
Alpha channels are commonly used in video-effects applications. InDesign automatically recognizes Photoshop’s default transparency (the checkerboard background) as an alpha channel. If the graphic has an opaque background, you must use Photoshop to remove the background, or create and save one or more alpha channels with the graphic. You can create alpha channels using background-removal features in Adobe
Photoshop, such as layer masks, the Channels panel, the Background Eraser, or the Magic Eraser.
Results of using alpha channels and embedded paths
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A. Original graphic B. Alpha channel C. Placed graphic D. Original graphic E. Graphic with embedded path F. Placed graphic
When you place a Photoshop file, the Image Import Options dialog box lets you choose to use the default clipping path or select an alpha channel for clipping.
1. Select an imported graphic, and choose Object > Clipping Path.
2. In the Clipping Path dialog box, choose either Photoshop Path or Alpha Channel from the Type menu.
3. Choose the desired path or alpha channel from either the Path or Alpha menu.
Note: If the Alpha Channel menu command is not available, no alpha channels were saved with the graphic.
4. To inset the clipping path, specify a value for Inset Frame.
5. To switch the visible and hidden areas, select Invert.
6. If you chose an alpha channel, specify any other desired clipping path options, and click OK.
To turn off the clipping path, select the imported graphic, and choose Object > Clipping Path. Choose None in the Type menu, and click OK.
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Create a clipping path automatically
If you want to remove the background from a graphic that wasn’t saved with a clipping path, you can do it automatically using the Detect Edges option in the Clipping Path dialog box. The Detect Edges option hides the lightest or darkest areas of a graphic, so it works best when the subject is set against a solid white or black background.
Good (left) and bad (right) candidates for automatic clipping path
1. Select an imported graphic, and choose Object > Clipping Path.
2. In the Clipping Path dialog box, choose Detect Edges in the Type menu. By default, the lightest tones are excluded; to exclude the darkest tones, also select the Invert option.
3. Specify the clipping path options, and click OK.
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Clipping path options
Threshold Specifies the darkest pixel value that will define the resulting clipping path. Increasing this value makes more pixels transparent by extending the range of lightness values added to the hidden area, starting from 0 (white). For example, if you want to remove a very light drop shadow when using Detect Edges, try increasing the Threshold until the shadow disappears. If light pixels that should be visible are invisible, the
Threshold is too high.
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Threshold levels at 25 (left) and 55 (right)
Tolerance Specifies how similar a pixel’s lightness value can be to the Threshold value before the pixel is hidden by the clipping path. Increasing the Tolerance value is useful for removing unwanted bumps caused by stray pixels that are darker than, but close to the lightness value of, the
Threshold value. Higher Tolerance values usually create a smoother, looser clipping path, by increasing the range of values near the Tolerance value within which stray darker pixels are included. Decreasing the Tolerance value is like tightening the clipping path around smaller variations in value. Lower Tolerance values create a rougher clipping path by adding anchor points, which may make it harder to print the image.
Tolerance levels at 0 (left) and 5 (right)
Inset Frame Shrinks the resulting clipping path relative to the clipping path defined by the Threshold and Tolerance values. Unlike Threshold and
Tolerance, the Inset Frame value does not take lightness values into account; instead, it uniformly shrinks the shape of the clipping path. Adjusting the Inset Frame value slightly may help hide stray pixels that could not be eliminated by using the Threshold and Tolerance values. Enter a negative value to make the resulting clipping path larger than the clipping path defined by the Threshold and Tolerance values.
Inset frame at -0p1 (left) and 0p3 (right)
Invert Switches the visible and hidden areas, by starting the clipping path with the darkest tones.
Include Inside Edges Makes areas transparent if they exist inside the original clipping path, and if their lightness values are within the Threshold and Tolerance ranges. By default, the Clipping Path command makes only the outer areas transparent, so use Include Inside Edges to correctly represent “holes” in a graphic. This option works best when the brightness levels of areas you want to make transparent don’t match any areas that must be visible. For example, if you choose Include Inside Edges for a graphic of silver eyeglasses, and the lenses become transparent, very light areas of the eyeglass frame may also become transparent. If areas become transparent when that wasn’t your intent, try adjusting the
Threshold, Tolerance, and Inset Frame values.
Restrict to Frame Creates a clipping path that stops at the visible edge of the graphic. This can result in a simpler path when you use the graphic’s frame to crop the graphic.
Use High Resolution Image Calculates transparent areas using the actual file, for maximum precision. Deselect this option to calculate transparency based on the screen display resolution, which is faster but less precise. This option isn’t available if you chose Alpha Channel, because InDesign always uses an alpha channel at its actual resolution. (See About transparency.)
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Convert a clipping path to a graphics frame
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Choose Object > Clipping Path > Convert Clipping Path To Frame.
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Create and edit alpha channel masks
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