Some Notes on Sizing Images: Part 5, Changing Image SizeRemember this screen from yesterday?
Now we learn how to change the image size. So long as Constrain Proportions is checked, when one things shifts, everything will. But generally you'll either want to change the size and keep the resolution the same, or change the size and resolution simultaneously. To do so, uncheck Resample Image. Now if you change the size (or pixel dimensions), now the resolution will remain the same and the image editor will make the necessary changes to the image to make everything.
So say that you have a 4x5 inch image at 300 dpi and you want the same size, but a lower resolution because you want it on the web and there's no need to use extra storage and take longer to downlond. So change the 300 dpi to 96 dpi and then click the OK button.
You can enlarge the image size or resolution, as well. Go back and recheck Resample Image. (Don't worry about the method - bicubic will do fine for now.) Now try changing the size. The resolution remains the same becuase the software is calculating what necessry changes to make.
Making an image smaller is always easier than making it larger, because in the first case you toss out informaiton, and in the latter, the software must make a calculated guess as to what additional image information it would need to fill in all those spaces that appeared when you spread the pixels out over a bigger distance. It's not perfect, but it's pretty good, and you'll have a larger image.