How to view a .SFF file online
No app, no account, no upload.
Open your .SFF
Drag a .SFF file onto the viewer, paste one with Ctrl+V, or choose it from your device.
View and inspect
Zoom in close, pan around, rotate or flip it, and read the exact color of any pixel.
Save a copy
Download it as PNG, JPG or WEBP with your rotation applied, at the quality you choose.
What is a .SFF file?
Everything worth knowing about Structured Fax File.
An SFF file is a Structured Fax File, a black-and-white fax image saved by ISDN fax adapters, most commonly AVM Fritz!Box or Fritz!Fax software. Open it with XnView (free) or IrfanView with the Plugins package. To convert to PDF or TIFF, use XnConvert (free).
Programs that open .SFF files
- Windows
- XnView, IrfanView, PMView Pro, XnConvert, Visendo Fax Server Express
- macOS
- XnView MP
- Linux
- XnView MP
| Full name | Structured Fax File |
|---|---|
| Developer | AVM GmbH (originated with ISDN/CAPI fax standard) |
| First released | circa 1993 (tied to CAPI 2.0 ISDN standard) |
| Category | Images |
| MIME type | image/x-sff |
| Signature | 53 66 66 66 ("Sfff" - 4-byte ASCII signature) |
Related tools
More free tools for working with images.
Frequently asked questions
Is my .SFF file uploaded to a server?
No. The viewer decodes your .SFF file with your browser's own image engine. Closing the tab removes it completely.
How do I open PSD, TIFF, RAW or HEIC files?
HEIC and HEIF (iPhone photos) open right here — we decode them with libheif. PSD, TIFF, JPEG 2000, camera RAW, HDR and texture files have their own viewers, linked above; the Image Viewer sends you to the right one automatically.
What does the Photo details panel show?
The EXIF data your camera or phone saved in the photo: camera and lens, shutter speed, aperture, ISO, the date it was taken and, if location was on, where. Files you save from this viewer don't include this data, which is handy when you share photos.
Is there a file size limit?
There's no fixed limit; it depends on available memory. Very large images (over 40 megapixels) are previewed at reduced resolution so the viewer stays fast, but the reported dimensions are always the original ones.
How does the color picker work?
Point at any pixel to see its HEX and RGB value with a magnified view of the surrounding pixels. Click to copy the HEX code and save it to your palette.
Should I save as PNG, JPG or WEBP?
PNG keeps every pixel and transparency, which is best for screenshots and graphics. JPG makes photos small. WEBP is usually the smallest of all and works in every modern browser.
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