Imagine a picture printed on the surface of a balloon that's inflated almost to the bursting point, and you've visualized some of what Adobe Photoshop's bulge effects can do. Photoshop also can create an inverted bulge that appears to suck an image inward on itself. The native Photoshop filters that accomplish these effects rank among the program's oldest plug-in options. They provide effective, quick results despite their bare-bones user interfaces, helping you accomplish imaging goals without investing in add-on software.
Open the Photoshop "Filter" menu and scroll down to its "Distort" submenu. Select "Pinch" from the list of Distort options to open the "Pinch" dialog box.
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Set the "Amount" value using the "Pinch" dialogue box slider control. Negative values extrude pixels outward; positive percentages pinch your image inward. If this seems counter-intuitive, remember the name of the filter.
Click on the "+" and "-" buttons below the preview window in the "Pinch" box to examine the preview more or less closely. When you're pleased with your results, click on the "OK" button to apply the filter to your image.
Open the Photoshop "Filter" menu and navigate to its "Distort" submenu. Choose "Spherize" from the list of Distort options to bring up the "Spherize" box.
Set the "Amount" value using its slider control or enter a percentage value between -100 and 100 in its data entry field. Choose "Normal," "Horizontal Only" or "Vertical Only" from the "Mode" drop-down menu to set the direction in which your effect applies. "Normal" makes image pixels balloon inward or outward. The two single-direction options apply the effect only on one axis, which looks more like selective scaling.
Use the "+" and "-" buttons below the effect preview window to zoom into or away from your image for a closer or more distant view. When you're satisfied with your settings, click on the "OK" button to apply the "Spherize" filter to your image.
Make a selection before you bring up the dialogue box for either of these effects so you can restrict the image area to which the filters apply.
Use the filter-application diagram in each filter's user interface to visualize how these effects apply to your image. The diagram shows your distortion settings applied to a matrix of two sets of parallel lines set perpendicular to each other at a 90-degree angle.
Unlike many of Photoshop's effects, Pinch and Spherize offer previews only in their dialogue boxes, not in the main document window.
At the extremes of their settings, these filters can introduce obvious distortion.