Changing the Canvas Size in Photoshop

I’ve probably harped on you to the point that you’re slightly paranoid, or at least ultraconscious, of using the Image Size command. Well, you can relax now because the Canvas Size command is as safe as can be. Unlike the Image Size command, which enlarges or reduces the dimensions or resolution of your image, the Canvas Size command merely changes the size of the canvas, or page, on which the image sits.

When you increase the size of the canvas, Photoshop fills the expanded area outside the image with your chosen color. Increasing your canvas size can come in handy if you are trying to add a frame or border around your image. If you make the canvas smaller, Photoshop crops (cuts away) the image.
Here are the quick and easy steps to changing your canvas size:

1. Choose Image➪Canvas Size.
The Canvas Size dialog box appears. The current size of your canvas appears at the top of the dialog box.

2. Enter new values in the Width and Height text boxes.
You can also change the unit of measurement by using the pop-up menus. Select the Relative check box to specify an amount of space for Photoshop to add around your image. This feature is handy when adding equal amounts of canvas around images with fractional measurements.

3. Specify your desired anchor placement.
The anchor shows how the image sits inside the canvas. By default, Photoshop centers the image and adds the canvas around it. Click any of the other eight squares to have Photoshop add the canvas asymmetrically around the image.

If you reduce either the Width or Height value and click OK, an alert box appears asking if you really want to proceed because you will be clipping the image. This is actually another way of cropping an image, albeit not one you will use everyday. Photoshop has more exact ways of cropping an image (see the next section). However, this method can occasionally come in handy when you want to crop your image on one or more sides by a certain number of pixels. For example, sometimes cropping (using the Crop tool described in the next section) a one- or two-pixel-wide row or column along the edge of an image is difficult.

In this case, use the Canvas Size command and specify a value for the Width and/or Height that is a couple of pixels smaller than your original. Pesky problem solved.

4. Choose your canvas color from the Canvas Extension color pop-up menu and click OK.
No longer do you have to be diligent in selecting a background color before you initiate the canvas size command. Photoshop now offers you the option of choosing the color you want for your newly expanded canvas. Choose from Foreground, Background, White, Black, Gray or Other. If you select Other, Photoshop transports you to the Color Picker where you can choose any color you desire. Note that the small swatch to the right of the pop-up menu displays the current background color. You can also click this swatch to access the Color Picker.