TN3 File Documentation
Summary
A .tn3 file is a Tiny high-resolution image from the Atari ST computer, the monochrome 640×400 member of the RLE-compressed “Tiny” picture family used in the late 1980s and early 1990s. It is an obsolete retro-computing format with no MIME type of its own (application/octet-stream). Mainstream photo viewers cannot decode it; the practical tools are RECOIL (a free retro-image decoder) or XnView MP with all graphic formats enabled. Almost always, what you want is to convert it to PNG.
Technical details
| Feature | Value |
|---|---|
| Full name | Tiny High-Resolution Image (Atari ST) |
| File extension | .tn3 (family: .tn1, .tn2, .tny) |
| MIME type | application/octet-stream |
| Format type | Binary raster bitmap, RLE-compressed (Atari “Tiny” format) |
| Resolution (TN3) | 640×400, monochrome (1 bitplane) |
| Platform | Atari ST family |
| Origin | “Tiny Stuff” / Tiny View utilities (David Mumper); Atari ST community |
| Introduced | Late 1980s / early 1990s |
| Status | Obsolete — retro-computing only |
| Open standard | No |
| Compression | Run-length encoding (RLE) of bitplane data |
| Signature | None; leading 1-byte resolution/flag code (2 = high-res static) |
| Colour | None — black and white (no palette in TN3) |
| Family variants | TN1 = 320×200 16-colour; TN2 = 640×200 4-colour; TN3 = 640×400 mono |
| Related extensions | .tn1, .tn2, .tny, .pi3, .neo, .degas |
| Modern decoder | RECOIL; XnView MP |
What is a TN3 file?
A .tn3 file is a Tiny image from the Atari ST family of computers, specifically the high-resolution monochrome member of the format. The Tiny format — also called “Tiny Stuff”, after David Mumper's Tiny Stuff conversion utility and the Tiny View viewer — was a popular way to store Atari ST screen images compactly in the late 1980s and early 1990s. It shrank the machine's otherwise raw bitplane screen data with run-length encoding (RLE), which is why a Tiny picture is much smaller on a floppy than an uncompressed screen dump.
The Tiny family has three members that match the Atari ST's three display modes: .tn1 for low resolution (320×200, 16 colours), .tn2 for medium resolution (640×200, 4 colours), and .tn3 for high resolution (640×400, monochrome, one bit per pixel). Some tools store all three under the generic .tny extension instead. TN3 is the black-and-white variant, so unlike TN1 and TN2 it has no colour palette. The format is long obsolete: it belongs to the Atari ST demoscene and hobbyist-art era and is produced by no current software.
The resolution byte and the RLE stream
A Tiny file has no ASCII magic string. It is identified by its extension plus the first byte, a resolution/flag code. Values 0, 1 and 2 denote static low, medium and high-resolution pictures; values 3, 4 and 5 denote animated variants that rotate the palette. A TN3 file therefore begins with the value 2, marking the 640×400 high-resolution static image.
Resolution byte Meaning
0 static low res (320x200, 16 colours) -> .tn1
1 static med res (640x200, 4 colours) -> .tn2
2 static high res (640x400, monochrome) -> .tn3
3,4,5 animated (colour-rotation) variantsFor the colour modes, palette data (Atari ST colour words) follows the leading byte; for TN3 there is no palette, because the image is one bitplane of black and white. After any palette comes the RLE control and data blocks: the run-length-encoded bitplane stream that a decoder expands back into the 640×400 screen. The exact byte layout of the high-resolution header has not been re-derived here from a primary Atari specification, so the resolution-byte mapping above is drawn from format references and should be treated as indicative rather than bit-verified. In practice you rely on a decoder that already knows the format rather than parsing it by hand.
Decoding a TN3 and converting it to PNG
Mainstream image viewers on Windows and macOS cannot open a .tn3, because it is an obscure RLE-compressed Atari format they were never taught. Two tools decode it. RECOIL (Retro Computer Image Library) is a free, open-source decoder built specifically for vintage-computer image formats, including the Atari Tiny family; it opens a .tn3 directly, and its recoil2png command-line tool converts one to PNG in a single step. XnView MP also reads the format once you enable Settings › General › “Show all graphic formats”, after which you can open and batch-convert.
PNG is the right conversion target for a TN3: it is lossless and handles a 1-bit monochrome bitmap cleanly. JPG is a poor choice for black-and-white line art because its lossy compression adds fuzz around sharp edges, so prefer PNG (or BMP if you need an uncompressed bitmap). The file itself is a static image with no scripting or executable content, so it is harmless to open; the only practical caution is that searching the web for a “TN3 viewer” can lead to adware-bundled “universal file viewers”, so stick to RECOIL or XnView MP from their official sites.
Frequently asked questions
How do I open a TN3 file?
Use RECOIL (free, open source) or XnView MP with “Show all graphic formats” enabled. Both decode Atari ST Tiny images and run on Windows, macOS and Linux. Standard Windows and macOS photo viewers cannot read the format.
What is the difference between TN1, TN2 and TN3?
They are the same Tiny format in the Atari ST's three display resolutions: TN1 is low-res 320×200 with 16 colours, TN2 is medium-res 640×200 with 4 colours, and TN3 is high-res 640×400 monochrome. TN3 alone has no colour palette.
How do I convert a TN3 to PNG?
Decode it with RECOIL (the recoil2png tool does it in one step) or open it in XnView MP and export to PNG. PNG is lossless and ideal for the monochrome bitmap; avoid JPG, which is lossy and unsuited to black-and-white images.
References
- RECOIL — Retro Computer Image Library (supported formats)
- Atari ST graphics file formats (EGFF reference)
- FileInfo — TN3 file extension
Feedback
Was this page helpful?
Glad to hear it! Please tell us how we can improve.
Sorry to hear that. Please tell us how we can improve.