What image upscaling can and cannot do
· 5 min read
Upscaling makes an image larger. It cannot make it more accurate. That distinction sounds pedantic until it matters, which is more often than people expect.
The difference between sharpening and inventing
Traditional upscaling interpolates: it works out intermediate pixels from their neighbours. The result is larger and softer, and nothing untrue has been added. Model-based upscaling instead predicts what detail plausibly belonged there, based on what similar images look like, and draws it in.
The second approach produces far better-looking results and is genuinely useful. It is also, strictly, making things up. The added detail is a good guess, not a recovery.
Where this is fine
- Making a small product photograph usable at a larger size on a page.
- Enlarging a graphic or illustration where exact texture does not carry information.
- Recovering readability of a heavily compressed image for your own reference.
- Preparing an old scan for print where some interpretation is acceptable.
Where it is not
- Anything evidential. Invented detail in a photograph used to establish a fact is worse than no detail.
- Faces of real people, where a model will confidently produce features that were never in the original.
- Text and numbers, where a plausible guess at a digit is indistinguishable from the correct one and just as legible.
- Medical, scientific or measurement images, where the output looks like data and is not.
The failure mode is not that it looks wrong. It is that it looks right. An upscaled licence plate or serial number is perfectly legible and may be entirely fictional.
How far you can push it
Doubling usually looks good. Quadrupling starts to show the model's assumptions, particularly in skin, fabric and foliage, where it tends to produce a texture that is too even. Beyond that you are mostly looking at the model rather than at the photograph.
Start from the best source you have
An upscaler amplifies whatever it is given, including JPEG artefacts, which it may interpret as texture and reinforce. If the original file exists somewhere at a higher resolution, using it beats upscaling a compressed copy every time. That is worth five minutes of searching before starting.
The upscaler here runs in the browser, which keeps a folder of client or family photographs on your own machine.
How to batch upscale images at 2x or 4x: enlarge a whole folder at 2x or 4x in your browser.
How to batch resize images to exact sizes, in your browser: presets for Instagram, YouTube and the web, and why a photo may not come out at exactly the preset size.
Frequently asked questions
Does upscaling restore lost detail?
No. It predicts plausible detail and draws it in. The result can look better and still be inaccurate, which is fine for presentation and not fine for evidence.
How much can I enlarge before it looks artificial?
Doubling is usually safe. At four times and beyond the model's assumptions become visible, especially in skin, fabric and foliage.
Should I upscale a JPEG or find the original?
Find the original. An upscaler can mistake compression artefacts for texture and reinforce them, so a cleaner source beats a better setting.