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Changing the image size

There are three ways to choose a file resolution:

  • When opening a raw digital photo, you should set the output resolution in the Camera Raw dialog (see page 38).
  • For a JPEG photo or other image that you need to change the resolution for, use the Image Size dialog after opening the file in Photoshop.
  • When scanning, set the input resolution to control how many pixels the device will capture.

Changing the image size without resampling

Via Image > Image Size (Ctrl-Alt-I/Cmd-Option-I), you can change the resolution of your file and/or its width and height. If you do so with the Resample Image option unchecked A (without resampling), the image quality will remain at its current level. This method is recommended for digital photos and scanned images.

By default, JPEG photos from a digital camera have a low resolution (72–180 ppi) and very large width and height dimensions, with a sufficient number of pixels for high-quality output (prints as large as 8″ x 10″)—provided you increase the resolution to the proper value. When you increase the resolution to suit your output device, the pixel dimensions will remain constant and the print dimensions will become smaller.

Unlike photos from a digital camera, scanned images usually have a high resolution and small size dimensions but also contain a high enough pixel count to produce large, high-quality prints. In this case, you should change the width and height with Resample Image unchecked (thereby keeping the resolution and pixel count constant).

Changing the image size with resampling

If your file contains too few pixels to meet the resolution requirement of your target output device, you’ll have to increase the resolution with Resample Image checked. B This will add pixels to the file (increase its pixel dimensions) and increase its storage size accordingly. You should increase the resolution only to a level that is necessary to achieve the desired output quality.

When you downsample a file (decrease its resolution with Resample Image checked), pixels are discarded permanently. For a Web graphic, downsampling isn’t an issue; users will view it on a computer display, which is a low-resolution device. For print output, try to avoid resampling, because it reduces the image sharpness (although you can use a sharpening filter to remedy blurring from a minor amount of resampling).

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