The next section is the document size. The default here is inches, but you can change it to cm, mm, points, picas, columns, or percent. For this course we'll only be dealing with inches. Also under print size is the resolution setting defined in either pixels/inch (ppi) or pixels/cm.
Now notice the link icons to the right of both the width and height entry fields. This means the height and width are linked together, so when you change the value of one, the other is changed proportionally. Try typing a number into any of those fields and observe how it affects both the height and width. To unlink the height and width, you can uncheck the "Constrain Proportions" check box. You'll rarely want to do this, though, because it distorts your image.
The Resample checkbox determines whether or not you preserve the pixel data in the image and it has a direct effect on the resolution field of the image size dialog. Resampling an image always involves a change in the pixel dimensions. The general rule is this:
- When you are changing the screen size of an image you usually want to select the resample checkbox, modify the pixel dimensions, and set the resolution to 72.
- When you are changing the print size of an image you will generally want to leave the resample box unselected, and either adjust the print dimensions or the resolution to get the results you need.
- As you increase the print dimensions, your resolution decreases (thus, print quality decreases).
- As you increase resolution, the print size must decrease based on the amount of pixel data available.