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- A useful tool for documents you want to print. Measures the literal dimensions of printed image.
- Document can be resized in percentages, inches, picas, centimeters, millimeters, or points.
- Resolution is the quality of the document---how many pixels of color within one inch.
- Increased resolution means a larger file so for web or computer use 72 pixels/inch is usually sufficient.
Constrain proportions
You can choose to unconstrain the proportions to change the width without affecting the height (and vice versa) by unchecking the "Constrain Proportions" checkbox at the bottom of the Image Size dialog box. Essentially, unchecking it stretches your document. Another way to check or uncheck constrain proportions is by locking or unlocking the chain image on the right side, as seen in the screenshot here.
Resample Image
Turn on when you don't want Photoshop to "invent" pixels when you are increasing the size of a file.
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