Upscale an image four times larger
Quadruple the width and height of an image — sixteen times the pixels — with a model that rebuilds detail as it enlarges. The 4x setting is already selected.
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Best on small or low-resolution images, where there is most to recover.
What four times actually means
A 4x upscale multiplies both dimensions by four, so a 500 by 400 image becomes 2000 by 1600. That is sixteen times as many pixels, and every one of the fifteen new pixels around each original has to be predicted. It is a far more demanding job than doubling, which is worth knowing before judging the result.
When 4x is the right choice
It earns its keep when you need a specific large output from a genuinely small source: a print from a web-sized photograph, an old image that needs to fill a modern screen, or artwork that only survives at thumbnail size. If you only need a moderate increase, 2x will give you a cleaner result, because the model has to invent far less.
Two passes are sometimes better than one
If a 4x result looks over-smoothed or slightly artificial, try running 2x twice instead. Each pass makes a smaller leap and has more real information to work from on the second run. It takes longer and it is not always better, but on difficult images it is worth comparing before settling.
Frequently asked questions
Why is 4x slower than 2x?
It produces four times as many output pixels and runs a heavier model to do it. The image is also processed in overlapping tiles, and a larger output means more tiles, so the time adds up on both counts.
Is there a size limit on what I can upload?
Yes, there is a ceiling on the input dimensions, because a large image at 4x produces an enormous output and a very long job. If your image is refused for being too large, it is already big enough that 2x will serve you better anyway.
Can I print the result?
Often, yes, and this is one of the better uses for it. At 300 dpi a 2000-pixel-wide image prints cleanly at about 17 cm across. Judge the output at full size before committing to a large print, since flaws invisible on screen become obvious on paper.