When you go to File: New and create a new document you have the choice of selecting a resolution right then and there or you can do it at a later time.

It's important to understand resolution a bit more if you are completely lost.  Basically 72 dpi (dots per inch) is 72 dpi X 72 dpi
(height & width) which equals 5184 pixels (of information) within a square inch.

When you have 300 dpi, there are 90,000 pixels in a square inch.  I hope you are with me (or this could get messy). The standard resolution for web is 72 dpi. This is the resolution that works nicely on computer screens.  If you print an image at 72 dpi and enlarge the image beyond its original size, you're going to start losing quality.  So if you know that you're scanning in an image and only going to use it for web you could keep it at 72 dpi.

I recommend scanning (film..) prints at 720 dpi because that way, if you know that you might be making enlargements, the quality is going to be a lot better down the road (as long as you have space to store your files).

You can always go down in resolution but you can never go up.  That is the key thing to remember.  For example, if you have a 720 dpi image (tons of image information squeezed into that same inch) you can bring it down to say 300 and you'll be fine. If you try to enlarge a 72 dpi image to 720 it can't make up those new condensed pixels it never had in the first place so they become blockier.

300 dpi is the minimum standard for print. So just think about which method you're going to use the most. 300 should work fine for you unless you plan on doing poster-size prints @ 720 dpi. The larger the resolution also equals the larger the file size. So keep that in mind. There's no need to have 720 dpi for web because no one can discern the pixels that close together anyways (and you'd have to shrink the image size down).

It's just good information to know in case you are new to digital imaging.  You can upload pictures from your digital camera to your computer (unless it was made in Antarctica) but oftentimes you won't have control over the resolution.  Remember you can always go down in resolution (and you can change the image size accordingly) but never up without losing quality.  Keep this in mind when you are saving files.

If you know you might print an image, keep an original at a higher resolution and then you can work with anything for the web a lower resolution.  Remember that you can just go to File: Save As and save a file in any format you choose and it will save a copy as long as you choose a different file name or different format (otherwise Photoshop will override the current file).

The beauty with vector images or files (shapes, paths, text..) is that they retain their clarity and do not lose quality when you enlarge them.

Here's an important tip for any Photoshop Designer: Sometimes when you import a layer with a lower resolution the entire file will convert to that lower resolution without your knowledge. If you want to bring the resolution back up and merge layers or flatten the image: flatten layers AFTER you change the image size or resolution because you WILL lose image quality (even vectors!) if you flatten the image and then enlarge it.  So there's some more information for you on resolution.  To find out more, click here for a tutorial from Basic Photoshop.com

- Article by Orion Williams copyright 2004