Image Upscaler - Enlarge Images 2x, 3x and 4x Online

What This Upscaler Does

This tool enlarges an image with Lanczos resampling and then restores edge contrast with an unsharp mask. Both steps happen on your own device. It is worth being plain about what that does and does not mean, because the category is full of tools that imply otherwise: nothing here invents detail that was not captured. If a face is six pixels wide in your source, no amount of enlargement will reveal its features. What good resampling changes is how faithfully the detail that *is* present survives being made bigger. The default in every browser is bilinear interpolation — each new pixel is blended from the four source pixels nearest to it — which is fast, and which produces the soft, slightly plastic result people mean when they say an enlargement looks blurry. Lanczos instead weighs a 6×6 neighbourhood with a windowed sinc function, the same class of filter ImageMagick, GIMP and desktop photo editors reach for. Edges come out defined rather than smeared, and gradients stay smooth instead of banding. Two details do most of the quality work. The filter is applied separably — one horizontal pass, one vertical — which gives a result identical to the full 2-D convolution while costing twelve samples per pixel instead of thirty-six, and that is the difference between seconds and minutes on a large photo. And colour is premultiplied by its alpha before filtering, so the transparent parts of a cut-out PNG cannot bleed a dark fringe into its visible edges. The arithmetic runs in a background thread, which is why the progress bar keeps moving and the page keeps scrolling while a 4× job is under way.