Terminology: ppi stands for pixels per inch. This is the number of pixels that line up to measure one inch. Computer displays typically show 72 ppi, while printers can exceed 1200 ppi.
How to Resize an Image
Start Photoshop and open the image that you want to resize. The File > Open menu is common to both Photoshop and Photoshop Elements. For a RAW image, another dialog will open with additional options. After the file is open, locate the Image Size menu entry:
Elements: Image > Resize > Image Size
Photoshop: Image > Image Size
Below is a screen capture of the Image Size dialog box from Photoshop Elements 10. Make sure Constrain Proportions is checked in order to preserve the image's aspect ratio. Uncheck the option Resample Image. Then set either the width or the height, and the other dimension will be recalculated for you. Or, set the Resolution and the width and height will be calculated. When selecting Resolution, realize that most computer monitors display somewhere between 72 and 96 ppi. Finally, click OK to resize the image.
There are Resampling options that you can play with using the dropdown box that allows you to select an interpolation algorithm. Only resample if you know why you are doing so, and be aware of the consequences. You will either lose data if you make the image smaller, or you will allow Photoshop to invent data that is not in your original image when you enlarge.
Resampling for print is generally not recommended. A printer uses much higher resolution when putting dots on paper. A quality photo printer is capable of printing at 1440 dpi (dots per inch) or higher. After you set the size, it is often best to let the printer driver take care of any resampling that is required for an optimum printed image.
Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
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