This tutorial will address Photoshop's two methods of resizing documents as well as how to use both image size and canvas size.

Image Size

The function of image size is to allow Photoshop users to increase or decrease the size of their work. This is a crucial step in preparing your document for print, web, or whatever else you might have in mind.

To access options, go to Image > Image Size or use the keyboard shortcut, Command+Option+I.

Pixel dimensions

  • This section tells you the file size (M stands for megabytes).
  • The width and height of the file in pixels can be set in terms of either pixels or ratios.

Document size

  • 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.

TIP: Hold down option key and clicking the cancel button resets the dialog box back to what it was when opened.

Canvas Size

The difference between image size and canvas size is that in the case of the former, the entire document becomes proportionally larger, whereas with canvas size, the layers of the document stay the same size, but the canvas (the background/bottom layer) increases in size.

To access, go to Image > Canvas Size. The keyboard shortcut is Option+Command+C.

The first thing the canvas size dialog box provides is the current width and height of your document for reference. You can change the size of the document in terms of percentages, inches, picas, centimeters, millimeters, or points. Therelative checkbox determines whether you want to size your canvas in absolute or relative terms.

The anchor

A highly useful tool for resizing the canvas. Click the direction from which you want the current document to be "anchored" and the new part of the document will extend out from the opposite direction. For example, here the document has been anchored from the left. If you do not check any direction it will extend from both sides.

Canvas extension color

The canvas extension color will be the same color as your background unless you set it as something else in the canvas size box.

TIP: Holding down the option key will turn the cancel button into a "reset" button which takes all settings back to what they were when you opened the dialog box.

Below, the finished product: an additional 4 inches of canvas on right side.