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About this tool
Enlarge an image in your browser using Lanczos, bicubic, bilinear or nearest-neighbour resampling with optional sharpening.
Upscale Image enlarges a picture in your browser by resampling it with a real reconstruction filter — Lanczos 3, bicubic Catmull-Rom, bilinear or nearest neighbour — rather than letting the browser stretch it. Each output pixel is a normalised weighted average of the source pixels around the matching position, with alpha handled in premultiplied form so transparent areas cannot bleed colour into opaque ones. It is for anyone who needs a larger version of a logo, screenshot or photo without sending the file to a server.
Open Upscale Image on AltFTool — it loads instantly in your browser.
Upload or drag in the file you want to work with.
Adjust the settings and preview the result.
Download the finished file to your device.
Lanczos 3, bicubic Catmull-Rom, bilinear and nearest neighbour, each with its own trade-off.
Colour is convolved premultiplied by alpha, so PNG edges do not pick up dark fringes.
Decoding, resampling and encoding all run in the browser tab on your own machine.
Lanczos 3 for photographs, because its 3-tap sinc window keeps the most fine detail; bicubic Catmull-Rom for a softer, ring-free result; and nearest neighbour for pixel art and screenshots of text, where you want the blocks to stay hard-edged.
No. Resampling redistributes the information already present, so a 400 px photo enlarged to 1600 px has the same real detail spread over 16 times as many pixels. Only a trained AI model invents new detail, and that is not what this tool does.
Bicubic uses a cubic polynomial over a 4-pixel window (radius 2); Lanczos 3 uses a windowed sinc over a 6-pixel window (radius 3). Lanczos preserves more high-frequency detail but can show a faint halo, called ringing, next to very hard edges.
Up to 40 megapixels of output, which is roughly 8000 × 5000 pixels. Beyond that a single RGBA buffer exceeds about 160 MB and most browser tabs run out of memory, so the tool stops and tells you to pick a smaller scale.