JFIF 转 JPG 转换器

JFIF (JPEG File Interchange Format) is the file layout from the early 1990s that most JPEG images use; the letters "JFIF" sit in the first few bytes of millions of ordinary .jpg files. You only see the extension when software picks .jfif as the name. The common cause is a Windows registry entry that maps the image/jpeg content type to the .jfif extension; Chromium-based browsers read that entry when saving a picture, so a photo downloaded from a website lands as image.jfif.

The file itself is fine. What breaks is everything that judges by extension: upload forms, older photo viewers and print services that list JPG and PNG and grey out anything else.

Since the data inside is already JPEG, decoding and re-encoding it would only cost quality. The tool checks the first three bytes for the JPEG signature (FF D8 FF) and, when it matches, writes the same bytes under a .jpg name. A 312 KB .jfif becomes a 312 KB .jpg, identical down to the last byte, with its EXIF data and colour profile intact.

The check exists because a .jfif name is not proof of JPEG content. If the bytes turn out to be something else, the image is decoded and saved as a real JPEG at 92% quality instead, so the result always opens as a .jpg. If you want a lossless file in a different format, the JFIF to PNG page decodes the same file into a PNG.

Converting fixes the files you already have; a registry change stops new ones. In Registry Editor, open HKEY_CLASSES_ROOT\MIME\Database\Content Type\image/jpeg and set the Extension value to .jpg. After restarting the browser, Save image as should offer .jpg again. Editing the registry affects the whole system, so if you would rather not touch it, keep this page for the occasional batch of downloads instead.

Pictures saved from the web can include screenshots of messages, receipts or other people’s photos, so the rename runs inside your browser tab. The .jfif files are read from your disk, renamed in memory and offered back as downloads; nothing is sent to a server. Drop up to 30 files at a time (50 MB each) and save them one by one or as a single ZIP.