Convert Many Images to One Format

The format you pick applies to every file in the queue, whatever mix arrived — a screenshot, a photo and a logo can all go in together and all come out the format you chose. That is the difference from converting one file at a time on the single-file converter: here the decision is made once, for the whole folder.

A JPEG has already thrown away the detail its quality setting discarded, and writing it into a lossless PNG afterwards cannot bring any of that back — it only stops a FURTHER loss on any future re-save. The visible result is the same picture in a usually larger file.

JPEG cannot store transparency at all, so a see-through pixel has to become some solid colour on the way out. Resizo places it on white by default, with black and a custom colour offered beside it — the same choice a visitor would make placing a logo on a page background. PNG and WebP outputs need no such decision: both keep the transparency exactly as it was.

PNG has no quality dial — it stores every pixel exactly, which is precisely what makes it lossless and precisely why it cannot chase a smaller number the way JPEG or WebP can. A busy photograph converted from JPEG to PNG typically comes back several times larger for an identical picture, because a JPEG at typical quality is already smaller than a lossless PNG of the same detail can ever be.

WebP usually produces the smallest file of the three at a comparable quality, which is why it is the default output here — but output size depends on the image and the quality setting, not on the format name alone. A flat, simple graphic or a photo already compressed hard elsewhere can land close to its starting size in any format.

A JPEG asked to become a JPEG is not run through the encoder again — it is handed back exactly as it arrived, metadata included, because re-encoding it could only cost quality or grow the file for a picture that already is what was asked for. The row for that file says so, and it still downloads and still joins the ZIP.

Every file in the batch is decoded, measured and re-encoded by code this page hands to your own browser, so nothing is uploaded and there is no copy of it anywhere else for this to work. The ZIP, when you ask for one, is built on your device too, from the files already sitting in its memory.

Up to 20 images or 80 MB total, whichever is reached first, can go into one batch. A folder works the same way as a multi-file pick, and Resizo counts what it found before adding anything, so you are told the moment it can hold no more rather than after the fact.

Five real conversions from a measured run, each one a different source and target format.

Before

After

1. Choose your images. Drop up to 20 JPEG, PNG or WebP files onto the panel, or press Choose images. A whole folder works the same way, wherever the browser allows picking one.
2. Pick one output format. Choose JPG, PNG or WebP as the single format the entire batch will become — it applies to every file in the queue, whatever format each one arrived in.
3. Set the quality, or the background if it applies. JPG and WebP take a quality dial; PNG has none, being lossless. Converting to JPG also asks where a transparent picture’s see-through areas should land — white, black, or a colour you pick.
4. Press Convert and download. Watch each file settle as it finishes, then download results one at a time or together as a ZIP — a file that could not convert says why, right beside the ones that did.