Resizing the images to 300 DPI isn't going to make them print better if they were originally at 72 DPI, it will just make the file size quite a bit bigger. It's pretty hard to raise the resolution of low-resolution files without specialized software. But if you're sending them to a place to have them printed, 4x6's or something small like that, and they require 300 DPI, then here's how to do it:
Open a picture (not one of the ones you'll be changing) and go to your Actions palette (if it's not visible, go to Window, then click Actions). Click the "Create new action" button, give it a name, click OK. Go to Image, then Image Size, and change the DPI to 300. Make sure all the checkboxes at the bottom are checked, and change the Resample Image dropdown to "Bilinear" or "Bicubic Smoother" (try both and see which one looks better), click OK. Go to File, then Save As, and choose where to save it. In your Actions palette, click the square "Stop playing/recording" button.
Now that you've made your action, go to File, then Automate, then Batch. Choose the action you just made in the Action dropdown. Choose "Folder" in the Source dropdown, and search for the folder with all your files (if there are multiple folders, you'll have to do this once for each folder). Change the Destination to "Folder" and navigate to the folder you want the files saved in. Check the box next to "Override Action Save As Command". In the File Naming dropdown boxes, make the first one "Document name" and the one to the right of that "extension". Click OK in the upper-right and let Photoshop do all the work for you
by ksimmonds on Thu Oct 15, 2009 3:22 pm