Scream of the Crop: How to Resize and Crop Photos - The Adobe Photoshop CC - page 249

Resizing for Poster-Sized Prints
So, since you saw earlier how much resolution you need to have to create a decent-sized
print, how do photographers get those huge poster-sized prints without having super-high-
megapixel cameras? It's easy—they upsize the images in Photoshop, and the good news
is that unless you need to resize your image by more than 300%, you can do this all right
in Photoshop without having to buy a separate resizing plug-in (but if you need more than
a 300% size increase, that's where those plug-ins, like OnOne Software's Perfect Resize,
really pay off).
Step One:
Open the photo you want to resize, then go under the Image menu and choose Image Size
or press Command-Option-I (PC: Ctrl-Alt-I) . When the Image Size dialog appears, to
the right of the Width field, you'll see a pop-up menu where Inches is chosen. Click on
that menu and choose Percent (as shown here). Both the Width and Height will change to
Percent, because they're linked together by default. Then, turn on the Resample checkbox
at the bottom.