Updated: Sep 26, 2020
This is something just about everyone needs to be able to do, and the good news is...it’s easy! Let’s start with image size.
First, open the image. Then go to ‘image > image size’. This window tells you everything you need to know about the current state of things.
You can change the width and height of the image. This will be a proportional change unless you click on the ‘link’ icon connecting those settings. However, the resolution setting is separate. If you have, say, an image that’s x wide and y tall at 72 dpi – and you want to find out what you’ve really got at 300 dpi, uncheck the ‘resample’ box. Then all three settings are linked, and a change to any one of them is reflected by a change in the other two. So, for example, a 10 x 20cm image at 150 dpi is the same as a 5 x 10 image at 300 dpi. And so on. That’s because when you uncheck ‘resample’, the pixel dimensions are locked. So either way, the image still contains exactly the same number of pixels – they’re just smaller, if you made the image smaller, or bigger.
Sounds good, doesn’t it? Well, unfortunately it’s too good to be completely true. All this is fine if you want to make an image smaller, but if you want to make it bigger you have a problem – because you’re spreading the same amount of detail over a larger area, and that just doesn’t lead to a high-quality result. Photoshop tries to help and offers various ‘resampling’ options, some designed to produce a better result if you’re enlarging an image. ‘Bicubic smoother’ and ‘preserve details’ among others.
But don’t lose heart: there is hope. Open a browser window, and enter
This is an incredible piece of kit. It’s called ‘ON1 Resize 2018’, and it costs...$59.99. That’s the whole thing, not an annual fee. And, it’s absolutely amazing. I’ve been using it and its predecessors for many years now, and I can honestly say it’s the Holy Grail of image enlargement. You can install it as a standalone app, or so that it runs within Photoshop. Here’s an example of what it can do: On the left, an enlargement made with Perfect Resize. On the right, the same enlargement made using Adobe Photoshop. And – no, I don't own shares in this program. I wish!