Image Size versus Canvas Size

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Today’s Question: I was wondering if you could explain the differences in Photoshop of canvas size and image size. I am confused as to their differences especially when printing. For example I would like to print as an 8×10 on 11.5 x 8.5 with an even white border all around. Is that possible?

Tim’s Quick Answer: Both the Image Size and Canvas Size commands in Photoshop allow you to change the overall dimensions of an image, but they operate in different ways. I think the best way to understand each of these commands is to consider when you would use each of them. The Image Size command is used when you want to change the size of an image, such as to print at a different size than the native pixel dimensions of the image. The Canvas Size command is used for adding space around a photo or essentially cropping the image by reducing the available space.

More Detail: For example, let’s assume you have an image that is currently sized at 8-inches by 12-inches at 300 pixels per inch (2,400 by 3,600 pixels). If you want to print that image at 20-inches by 30-inches, you need to change the pixel dimensions of the actual image. In other words, the image needs to be “stretched” to contain 6,000 by 9,000 pixels. In the process, pixel values need to be calculated for all of the “in between” pixels that are created when the photo is enlarged.

The Canvas Size command allows you to add space around an image, or to effectively crop an image. So, for example, let’s assume you want to print a photo at 11-inches by 17-inches, but on a 13-inch by 19-inch sheet of paper. This doesn’t actually require you to add canvas around the photo. If you print an image sized at 11×17 inches to a sheet of paper that is 13×19 inches, centering the printed image will automatically result in empty space around the photo.

However, let’s assume you want to have a colored border around the outside of the image, to simulate an effect similar to matting the image. You could use the Canvas Size command to add two inches to the width and height of the image, using an underlying color layer to apply the color to the “extra” space that is created around the photo.

What all of this really means is that for most photographers with typical workflows, the Image Size command is the only command you need when you need to adjust the output size of a photo. The Canvas Size command, however, can be very helpful in certain specialized situations, where you’re essentially going beyond simply working with the image and instead performing some tasks related to page layout.