How to Resize Images in Affinity Photo Desktop

by Apr 7, 2020Photo Editing Tutorials

Robin Whalley Landscape Photographer

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How to Resize Images in Affinity Photo Desktop

In this tutorial, I look at ways you can use to resize images in Affinity Photo. I’ll be covering several options that you can use depending on your needs. I’ll also discuss tips and do some pixel peeping to check the quality of the enlargements.

But if you only want to know the basic steps for resizing images in Affinity read the next section.

Affinity Photo Trial Software

If you don’t have the latest version of Affinity Photo you can download a trial from the Affinity Photo website.

The Quick Way to Resize Images in Affinity Photo

Before we get into the detail of this tutorial, if you’re just looking for a quick way to resize an image in Affinity Photo, here are the steps:

  1. Open the image you want to resize in Affinity Photo.
  2. If you’re working on a RAW file it will open in the Develop Persona. Before you can resize it, you need to click the “Develop” button. This converts it to an image and opens it in the Photo Persona. Image resizing is only available in the Affinity Photo Persona.
  3. In the Affinity “Photo Persona”, click the Document menu and select the “Resize Document…” option. This displays the resize dialog.
  4. In the resize dialog enter the new width or height of the image.
  5. If the dialog has the lock aspect ratio set, you’ll see the other image dimension updates automatically.
  6. Click the Resize button and Affinity Photo resizes the image.

Now if you want to understand the different options as well as learn other great ways to resize images, read on.

Resize Document Vs Resize Canvas

Something that confuses a lot of people when resizing images in Affinity Photo is, they find two resizing options in the menu. When you click the Document menu, you’ll see the “Resize Document…” and “Resize Canvas…” options.

affinity photo image resizing options in the document menu

To understand the difference and which to use, you need to know what the Canvas is. I should also point out that this option’s only available in the Photo Person. If you’re using one of the other Affinity Personas you won’t see the Document menu.

Every image you open in Affinity Photo has a canvas or work area. By default, the canvas has the same dimensions as the image, so the image covers and hides it. But by using the Resize Canvas option we can resize the canvas separately to the image.

Resize the Canvas in Affinity Photo

When you select Resize Canvas Affinity Photo displays the dialog above.

Locking the Canvas Aspect Ratio

In the top row you can see the current width and height of the canvas. To resize the canvas, enter the new dimensions.

Notice also the padlock icon between the two. This locks the aspect ratio between the width and height of the image. When you enter a new value for either, the other changes in proportion to keep the aspect ratio the same. If you click the padlock icon, it toggles between open and closed. When it’s open, changing the width or height doesn’t affect the other dimension.

Just below the width and height of the canvas you can see a dropdown displaying the word “Pixels”. This selects the unit of measurement when resizing the canvas. Try changing it to “Inches” and you’ll see the display for the width and height change.

Selecting the Anchor Point

The other control in the dialog is the Anchor. When Affinity Photo resizes the canvas, it uses the Anchor to position or anchor the image. In the example above you can see the anchor point is set in the centre. If I resize the canvas with this option, you’ll see the canvas appear around all the edges of the image.  Affinity positions the image in the centre of the canvas. That’s what allows the canvas to show around the edges.

Resized canvas in Affinity Photo showing around the edges of the image

Notice the canvas has a checked grey and white pattern showing the canvas is transparent. If I save the image in a format that doesn’t support transparency (like a JPEG) the transparent area turns white. You could use this to create a border or frame around the image.

It’s worth taking a minute to resize the canvas of an image using different anchor points. This will help you understand how to control the image placement.

Using the Resize Document Option

Another name for the image in Affinity Photo is the document. So, the Resize Document menu option is just another way to say resize the image. When you select the Resize Document option, you’ll see the resize dialog displayed.

image resizing options in the affinity photo resize dialog

In the top row of the dialog (number 1) you see the current width and height of the image. This works just like the canvas resizing explained above. Enter the new width and/or height for the image. You can also use padlock icon to lock or unlock the aspect ratio of the image.

Below this (number 2) you see the units for the image. Depending on why you’re resizing the image you might want to use one of the other units of measurement. For example, pixels might be useful when resizing an image for the internet. But if you want to resize an image for printing you might prefer to work in inches or millimetres.

Below this (number 3) is the DPI slider. You can use this to change the density of the pixels in the image. This can also affect the quality of the image and we’ll talk about it a little more shortly. Again, what you set this too will probably be determined by how you want to use the resized image.

The final section of the dialog (number 4) has the resampling options. These tie in closely with the DPI settings and we’ll look at the entire subject below.

When you’ve entered the new dimensions for the image and changed any settings, click the Resize button. Affinity Photo then resizes the image.

Up-Sampling or Down-Sampling the Image

When we increase the size of an image, we call it up-sampling. This involves adding new pixels into the image, causing the image to become larger. What’s important is Affinity Photo doesn’t randomly add the new pixels. Instead it uses a special Resampling method that calculates where to add the pixels, so the image looks good.

When we reduce the size of the image, we call it down-sampling. This requires removing pixels from the photo or image. As with up-sampling, Affinity Photo achieves this by resampling.

Resampling Options

When you’re resizing an image in Affinity Photo, you’ll notice there’s usually an option for Resampling. This is a special algorithm Affinity uses to determine where to add or remove the in the image. There are several you can chose but they’re not all good for every type of image.

Resampling options when resizing an image in Affinity Photo

Not every image you want to resize in Affinity Photo will be a photograph. Over time different resizing algorithms have developed from the basic to the highly complex. Which is best will depend on the type of image you’re working with and whether you’re up or down-sampling. Here’s a quick summary of the options:

  • “Nearest Neighbor” – Good for resizing images with hard edges like line art and diagrams.
  • “Bilinear” – General purpose algorithm which is good for down-sampling an image.
  • “Bicubic” – Another general-purpose algorithm but better suited for up-sampling images.
  • “Lanczos 3” (separable and non-separable) – These are complex algorithms which are very good for up-sampling images, especially photographs. The additional quality does come at the cost of taking longer to complete. If you want to resize a photograph to the highest quality, these are the options to use.

For photography enlargements the Bicubic and Lanczos 3 resampling should produce the best results. Here’s a section of an image viewed at 100% after the resizing the image to three times its original dimensions.

comparing image resizing using bicubic and Lanczos 3

Although there isn’t much between the two, the Lanczos 3 version looks slightly better on my computer monitor.

Resizing an Image without Resampling

Although we’ve been discussing up-sampling and down-sampling, it’s also possible to resize an image without resampling. It’s all to do with that DPI setting we mentioned earlier. If you uncheck the “Resample” option in the Resize dialog, you’ll find Affinity Photo disables all the options except for DPI and the Units dropdown.

resize dialog in Affinity Photo without resampling

The image is currently 6327px by 3405px. As the DPI is set to 240 the image measures 26.36 inches on its longest edge. You can work this out by dividing the number of pixels on that edge by the DPI; that’s 6327 / 240.

If we change the DPI setting to 96 the image still has the same pixel dimensions, but the actual size of the image has changed. It now measures 6327 / 96 which is 65.9 inches on the longest edge. All that’s happened is that Affinity Photo has spaced out the pixels in the image. That’s why we have the same number of pixels but a larger image.

Change the Units to Inches in the Resize dialog and you can see the new size of the image.

resizing an image by changing the dpi in affinity photo

But notice also the Size fields are enabled. It’s now possible to enter a new image size for the document in either the width or height field. When you do this, you’ll see the DPI change.

Affinity Photo is spacing out the pixels in the image to create the image size you want and it’s doing this without resampling. It doesn’t create new pixels and it doesn’t throw any away.

Now we can move on to look at other ways of resizing images.

What’s the Resize Pixel Art Document

The observant amongst you may have noticed an option to “Resize Pixel Art…” in the Affinity Photo Document menu. When you select this, you’ll see a dialog with limited resizing option.

Resize pixel art option in affinity photo

Here you can select to resize the image to 2x, 3x or 4x its current size. When you select one of these, Affinity Photo will up-sample the image to the new size by creating new pixels. There are two methods it can use which are HQX and XBR.

I couldn’t find out very much about these two methods of resizing other than XBR produces slightly smoother enlargements. Because of these I decided to compare the two by resizing my image to 3 times the original size. You can see the two small sections side by side below.

comparison between HQX and XBR resizing in affinity photo

This is a small section of the resized image viewed at 100% magnification. It’s difficult to see but HQX looks slightly sharper but there isn’t much between the two. For completeness, let’s compare HQX to Lanczos 3 resizing.

comparing Lanczos 3 with HQX resizing

Whilst you may not be able to see clearly in the screenshot, Lanczos 3 appears sharper and more detailed on my computer screen.

If you want to produce the highest quality enlargements for photography, resample using the Lanczos 3.

Resizing When Exporting

So far, we’ve been looking at ways to resize the image whilst you’re working on it. If you’re producing a big enlargement from your photo, you might not want to do this. A bigger photo means slower working and it’s possible your computer could struggle. A better alternative might be to resize the image during the export.

You may already know; Affinity Photo saves your images in a special Affinity Photo format. If you want to produce an image for sharing you need to export it using the export feature in Affinity. You’ll find Export in the File menu when you’re in either the Photo Persona or the Export Persona. Select Export and you’ll open the Export Dialog.

Affinity photo resizing in the export dialog

In the Export dialog you can select the type of image file you want to produce. In this example I’ve selected TIFF. At the top of the dialog you can again set the width and/or height of the resized image. Then further down you can see the dropdown to set the resampling method. We’ve covered both earlier in this tutorial.

Once you’ve set your options, click the Export button. This creates the new image using the chosen dimensions. Importantly, it’s only the exported image that’s resized. The image you have open in Affinity Photo is unchanged.

Resizing Images in Export Persona

Now how about being able to create multiple versions of your image at different sizes and in different formats. That’s exactly what you can do in the Affinity Photo Export Persona.

image resizing in the Affinity Photo export persona

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Here you can see the Slices Studio window. I haven’t created any slices, so any settings apply to the entire image.

Look at the Slices window and you can see it’s set to export two versions of the image (numbers 1 and 2). When we run the export routine, this produces images in both TIFF and JPEG formats from the image. The TIFF file will be 1x the size of the original image, in other words the same size.

If you look at the JPEG section, you’ll see it’s set to produce two version of the image. One will be twice the size of the original (2x) and the other three times the original (3x).

To run the export and produce the images, click the “Export Slices” button at the bottom of the window.

Summary of Resizing Images with Affinity Photo

As you’ve seen, Affinity Photo has lots of ways you can resize an image. Which is best depends on whether you are up-sampling or down-sampling the image as well as what the image is. If you’re a photographer reading this, the Lanczos 3 resampling method will probably produce the highest quality enlargements. For other types of image, use the resampling method most suited to that type of image.

Whilst I didn’t expect the results to be very good when using the Resize Pixel Art option, both methods are surprisingly good. Although I’m unclear what “Pixel Art” is (because the Affinity documentation is sketchy), I would happily use this to enlarge photography from the results I’ve seen.

For down-sampling images use the Bilinear resampling option.

More Affinity Photo Tutorials

You’ll find more high quality, free tutorials on my Affinity Photo Tutorials page.

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