If you use Adobe Photoshop as part of your business software toolkit, you manipulate image size in the course of preparing bitmapped graphics and photographs for use in your company's workflow. Reducing a document or a portion of its content can mean scaling it by eye or to known dimensions. Photoshop's roster of resizing operations includes options for working interactively or for making a picture smaller by specifying its destination size.
Adobe Photoshop's Image Size dialog box contains settings that enable you to resize an image to specific dimensions or to percentages of its original size. You can open this dialog box from the Image menu or by pressing "Alt-Ctrl-I." With the Resample Image and Constrain Proportions check boxes active, any reduction in width or height produces a corresponding reduction in the other dimension, yielding a smaller file size as well. With Resample Image deactivated, the resolution rises in value as Photoshop spreads more of the file's pixels across a smaller area. With Constrain Proportions unchecked, you can alter either width or height without changing both dimensions.
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To reduce an image by cropping it instead of downsampling or downsizing it, you can use Adobe Photoshop's Canvas Size dialog box, accessed from the Image menu or by pressing "Alt-Ctrl-C." With the Relative check box deactivated, the values you enter into the width or height fields become the final dimensions of the image. When you activate the Relative check box and enter a negative number in either dimension field, Photoshop reduces that dimension by the amount you enter. The proxy diagram in the Anchor section of the dialog box enables you to specify the position of the original image size in the altered dimensions. By default, Photoshop sets the proxy to the center and removes or adds canvas area to all four edges of the perimeter of the file.
Transform and Free Transform
Adobe Photoshop's Transform and Free Transform commands enable you to reduce the size of an image interactively. The Transform commands provide individual access to the group of commands combined into Free Transform, including the Scale option. To access Scale by itself, open the "Edit" menu and choose "Scale" from the Free Transform submenu. To enter Free Transform mode, choose the command from the Edit menu or press "Ctrl-T." In either case, you can scale image content by dragging any of the handles that surround the transformable area, which produces disproportionate results unless you hold down the "Shift" key while you drag. Holding down the "Alt" key – by itself or in combination with the "Shift" key – forces Photoshop to transform image content from its center. To reduce an image to a specific size, enter dimensions or percentages in the width and height fields in the Options bar. Click on the link button between the two dimension fields to produce proportionate results.
Save for Web and Devices
When you create versions of an Adobe Photoshop document for use on websites, the Save for Web & Devices dialog box gives you control over the optimization parameters you need for online implementation of file content. To access the Save for Web & Devices dialog box, open the "File" menu and choose it by name, or press "Shift-Alt-Ctrl-S." Among its many settings, this dialog box includes width and height fields you can use to specify destination size, as well as the resampling method Photoshop uses to interpolate file data. Unlike Photoshop's other scaling options, however, Save for Web & Devices does not include an option for disproportionate scaling by reduction percentage, although you can unlink width and height to reduce size disproportionately by dimension.
Information in this article applies to Adobe Photoshop CS6. It may differ slightly or significantly with other versions or products.