Batch Resize Images
Drop in a folder's worth of images, set a target size, and get them all back at once.
Options
All processing runs in your browser. No file leaves this device.
Most resizing tools, including the browser's own drawImage, average pixel values directly in the encoded sRGB domain. That is mathematically wrong. sRGB values are not proportional to light — the encoding curve is roughly a power of 2.2 — so averaging them underweights bright pixels. The visible consequence is that downscaled images come out subtly darker than the original, and the effect is strongest exactly where it is most noticeable: fine bright detail against a dark background, like stars, specular highlights, or backlit hair.
This tool converts to linear light first, averages there, then converts back. That is what "gamma-correct" means, and it is why the output holds its brightness. You can see the difference most clearly on a fine black-and-white checkerboard: correct resampling gives you mid-grey, naive resampling gives you something noticeably darker.
Five modes are available. "Fit within" bounds the long edge and preserves aspect ratio, which is what you want for web galleries. "Exact size" crops to fill a precise dimension. "By width" and "by height" constrain one axis. "By percentage" scales relative to each file's own size, which is the right choice when the batch contains mixed dimensions and you want them all reduced proportionally rather than forced to a common size.
Sharpening, if you add it in the pipeline tools, is applied after resizing — that ordering matters, because sharpening before a downscale throws away most of its own effect.
Common questions
- Why do my images look darker when other tools resize them?
- Because those tools average pixel values in the sRGB domain, where the numbers are not proportional to light. Bright pixels get underweighted and the result drifts dark. This tool averages in linear light instead, which is the physically correct operation.
- Will it enlarge images that are already smaller than the target?
- Not by default. "Never enlarge beyond original" is on, because upscaling invents detail that was never captured and usually looks worse than leaving the file alone. Turn it off if you specifically need every output at the same dimensions.
- How many images can I do at once?
- As many as your memory allows. Files are processed a few at a time across your CPU cores rather than all at once, so a large batch does not have to fit in memory simultaneously. Several hundred typical photos is routine.
- Are my images uploaded?
- No. Every step runs inside this page — decoding, the pixel maths, and encoding. Nothing is transmitted and no server receives your files. You can watch the Network tab in devtools while a batch runs, or simply go offline after the page has loaded.
This converter is part of a full editing pipeline — tone, colour, lens correction and batch export all run the same way, without uploading.
Open the full pipeline