While you can resize an image when you first start working on it, this step is best kept for later as a finishing adjustment. The reason for the late use of this tool is that you should always keep a master image that has had all the necessary adjustments, then resize it for specific uses (be sure you have a backup file by doing a "Save As" on the original). A digital image often will have multiple files of the photo, each identical except for the size.
Image sizing should only be done to the master, then create the file "saved as" with a new name to keep it separate (e.g., GS-trillium-5x7.tif). Resizing an image that already has been changed in size can cause quality issues. Unfortunately, software manufacturers haven't placed the size/resize tools in the same location in the menus. You may have to check the Help function. It's under the Image menu in Photoshop and Photoshop Elements.
There are several important points to consider when resizing an image. First, remember that the size of an image affects quality only in terms of how big it can be printed. Second, changing resolution only (ppi/dpi with Resample unchecked) has no effect on quality. Third, we can't overemphasize it—don't sharpen the master; only sharpen an image after the file has been resized.
|1 The size of your image file affects how large the image can be printed. Exceed the dimensions at a given resolution, and quality diminishes.
2 Resizing adjustments usually have three parts (the top to bottom order may change from software to software): Pixel Dimensions. This area shows the complete image size in pixels and megabytes; it becomes active when Resample is checked. Document Size. This reflects the output or print size of the image file at a given resolution in pixels per inch (although that can be changed for special purposes). Bottom. These special choices change how the image is resized and is where Resample is found; use Bicubic (or Bicubic Smoother).
3 Uncheck Resample Image and adjust the resolution to a printing resolution (200 to 300 pixels per inch); tweak the dimensions as needed. This step uses the native image size and keeps the image at its maximum quality.
4 If more of a size change is needed, check Resample and keep Bicubic, then change the relative dimensions as needed; be careful of too big a jump (more than twice the file size) and sharpen after the size change.