Size and Sharpen Photos
Digital photos have to be sized for specific uses. They are not like film. With film, you simply put the negative into an enlarger and make the picture bigger or smaller as needed. You cannot do that with a digital photo. For example, once a picture is resized to a small image, that small image cannot be resized with any quality to a big one.
In general, do all of your processing work on a photograph using a master Photoshop or PSD (Photoshop Document) file. Then save that master file for any future resizing purposes. The best way to do this is to create a new file for every new size of picture you need. You do not want to resize your master file, and then save over this version because you will not be able ...