Q) I would appreciate some help on resizing photos, particularly when to resample. Here's a scenario: I upload an image from my camera, and Photoshop Elements shows the resolution at 72 pixels per inch. I want to print the image at 4x6 at 300 dpi. Where in the procedure would it be best to resample?
A) You can make the needed changes in one step. However, I like to do it in two parts, leaving the resampling (which is interpolation) off until the second part. I first make changes just to see how big an image I can get based on a desired printing resolution for the image of 200 to 300 ppi/dpi.
In other words, with resampling turned off (unchecked), I change the ppi/dpi of the image to 200 or 300 and see what the new image dimensions are. This lets me know if I have enough resolution in the original file to make my print. If I do, I use the appropriate resolution size without resampling because I don't need to do any interpolation. If the image is larger or smaller than what I need, then I can size the image using interpolation, meaning checking the resample box. If you do resample an image to change its size, you'll usually need to sharpen it slightly, too.
A final pointer: If you decide to redo the size of your image after you've already interpolated it once, start over with the original image. Avoid re-interpolating an image.