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.
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.
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.
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.
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.
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.
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.
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.
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.
