The many ways to give your pics the high-res makeover
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On the surface, upscaling a photo seems like a simple enough task. You open your photo editing tool of choice, find the size adjustment menu, enter the new size for your photo and the app does the rest. Forget photo editing tools. Even the default photo viewer on your Mac or Windows PC can do it.
But the results of upscaling are often inconsistent. It can be annoying to see an old family photo look even blurrier after running it through an image upscaler. It's even worse with pixel art, which becomes a paint splotch with a vague outline after you upscale it 4x. Fortunately, these issues can be minimized if you use the correct method for the kind of photo you're upscaling.
Format is another consideration, which is determined by whether you'll edit it, the composition of the photo and its overall purpose.
How traditonal upscaling works
Conventional upscaling methods work on the basic principle of adding new pixels that are an average of those surrounding them. The difference is how many pixels are being factored into that average and the weight assigned to each. For this reason, traditional upscaling won't magically make your photos more detailed.
Nearest-neighbor upscaling is an exception to the pixel-averaging principle because it simply copies the nearest pixel wholesale. This makes it perfect for pixel art, diagrams and solid geometric shapes, as it retains their blocky appearance. But on regular photos and anything with a gradient, nearest-neighbor introduces aliasing, which makes the edges look pixelated.
A step up from nearest-neighbor is bilinear upscaling, which creates a new pixel by taking an average of its four surrounding pixels. This method doesn't produce a blocky look but can often make images overly soft, as if they're slightly out of focus. Use it for images that aren't sharp to begin with. Avoid it for upscaling close-up shots and anything else with fine details.
Bicubic upscaling strikes a good balance between resource usage and image quality. Instead of four pixels, it considers the surrounding 16 pixels, with more weight given to the closest ones. Thanks to this, it produces sharper images than bilinear upscaling, all without the jagged edges seen in nearest-neighbor upscaling. It's a safe bet for most types of photos, but know that it can introduce halos unlike the previous two methods.
There are other more sophisticated upscaling algorithms such as the Lanczos method. But these take up more processing power, and I didn't find the results that much better than bicubic upscaling. Try Lanczos only if you're dissatisfied with bicubic upscaling.
What about AI upscaling?
Where traditional upscaling methods add new pixels based on the surrounding ones, AI upscaling uses prediction. It works by creating a new image, which, when shrunk down, would most closely resemble the one that you asked it to upscale. And it can do so because AI models are trained on millions of high-resolution images.
Images upscaled using AI often look noticeably cleaner and more saturated. This makes a big difference when the source images are degraded, and you want the gaps filled in without too much focus on accuracy. Say you have an old, grainy photo taken in 2001: Traditional upscaling would make the image more high-res, but it won't remove the grain. An AI upscaler will make the image bigger while removing the grain too.
But these AI upscalers can have unintended effects too. For example, I ran the album art of Boards of Canada's album, Music Has The Right To Children, through PicsArt's AI image upscaler. It added eyes to a face that was blurred out in the original album art. This happened because faces usually have eyes, and it assumed this one does too. It wasn't extrapolating based on the source image but creating a new, larger image. The takeaway here is to not use AI upscaling on photos where accuracy is of utmost importance.
Don't forget the image format
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Image formats play an important role in deciding what you can do with an image. JPEG is the most widely compatible photo format. Your camera, phone and computer can all open it. Since it's a lossy format, the file sizes are small too, making it ideal for storing large photo libraries. However, it doesn't support transparency, so avoid using JPEG for stuff like logos or text.
For a good mix of quality and editing support, the PNG format is a solid choice. PNG images can be edited in almost all image editing programs and support an optional alpha channel, which adds transparency. Unlike JPEGs, PNG images don't lose quality when they're decoded and encoded during editing. This makes the format perfect for logos, illustrations and screenshots where detail is paramount. Using it for regular photos may be overkill considering it's a lossless format with a much larger file size than JPEG.
While you can get away with using the JPEG format for images you'll use on a website, a better format is Google's own WebP, which has been around since 2010. WebP images are about a quarter the size of PNG, and anywhere between 25 and 34 percent that of JPEG. This directly translates to faster loading times for your website.
If your primary devices are an iPhone and a Mac, stick with the default HEIC format. According to Apple, they're about half the size of standard JPEG images and store the same amount of detail. They also retain their editing history when you edit them using the Photos app on iPhone. However, HEIC has limited compatibility outside the Apple ecosystem: You will need to download third-party extensions and image viewers to view HEIC photos on a Windows system.
