Understanding Image Resizing in Photoshop

By Brendan Albano

Resizing images in Photoshop allows you to print images at the size you desire, and/or control their size for use on the web.

It may seem basic, but if you aren’t 100% confident you know how image size, print size, and dpi all relate to each other, and what the “Resample Image” checkbox does, please read this before bringing images to be printed in the AHVA Digital Lab.

In Photoshop, image size is found in the Image menu, Image>Image size.

You are now presented with the image size menu.

On the top are the “Pixel Dimensions” width, and height. You can choose between displaying this information as pixels or a percentage in the drop down menu. You generally will want to use pixels.

The pixel dimensions are the size of the image on the computer—they represent the size of the digital file.

Beneath pixel dimensions is the “Document Size” width, height, and resolution. You can choose between a number of options, for printing things in the lab at UBC you should use inches and pixels/inch.

Where the pixel dimensions width and height related to the size of the file on the computer, the document size width and height are the size it will be printed. The pixel dimensions and the document size are related by the resolution.

Resolution, also referred to as dpi (dots per inch) or pixels/inch (pixels per inch), is the relation between the pixel dimensions, and the print size, as expressed by the fraction pixels/inch. An image 3,000 pixels wide at 300 pixels/inch will be 10 inches wide. 3,000 / 300 = 10.

The resolution by itself does not mean anything without also understanding the pixel size. When someone tells you that to print a high quality photo you should print between 200 to 300 pixels/inch (or dpi), you also need to consider the pixel dimensions. This resolution will ensure a sharp print, but if you downloaded your image from the internet, and it is only 600 pixels wide, printing it at 300 dpi will result in a 2 inch wide print. 600 / 300 = 2. If this is not what you want, read on to learn how to resize your images!

Below "Document Size" are three checkboxes to do with resizing images.

Scale Styles

This option effects the scaling of layer styles. You will pretty much always want to have it checked.

Constrain Proportions

When “constrain proportions” is checked, your image will scale proportionally. When it is unchecked, you can scale the width and height separately, causing the image to be distorted. Usually you will want to have this box checked.

* In newer versions of Photoshop this checkbox is a lock icon that can be clicked to lock or unlock the proportions to one another.

Resample Image

This is the key to successful image resizing. When this button is unchecked, the pixel dimensions will be greyed out and you will not be able to edit them. You will only be able to change the document size. Photoshop will not create or delete any pixels, it just changes the resolution you will print them at, and the document size and the resolution will be linked.

When this button is checked, you will be able to change the pixel dimensions of the image, as well as set the document size and resolution independently.

What “Resample Image” means is that Photoshop will create or combine pixels in order to make the image the size you want it to be. Generally, it is best to leave the type of resampling to "Automatic" (unless you have a very clear understanding of resampling).

Try opening up an image in Photoshop and playing with these options so that you understand how they all affect each other.

  1. Make sure “Resample Image” and “Constrain Proportions” check boxes are checked.
  2. Set the document size (in inches) to the size you want to print at. (When sizing your image, remember, at UBC our paper comes in either a 16” roll and a 44” role and your image must be 1” smaller than the paper size to leave ½” margins.)
  3. Set the resolution to the desired print resolution. We recommend 300 pixels/inch.
  4. Make sure you have read How do I get prints made in the Binning Lab.