What is the EBM file format?
.ebm is the guild emblem file format used in Ragnarok Online, the MMORPG published by Gravity Co., Ltd. since 2002. Each file contains a 24×24 pixel, 8-bit (256-colour) guild emblem image stored as a zlib-compressed Windows .bmp bitmap.
When a player uploads a custom emblem, the game client compresses the raw BMP data into .ebm format and stores it in the client's /emblem/ directory. The uncompressed payload is always a standard Windows BMP of 1,734 bytes at 24×24 pixels with an 8-bit colour palette. Approximately 20% of .ebm files include a standard zlib wrapper (78 9C or 78 DA header) with an Adler-32 checksum; the remaining files are raw DEFLATE streams without the zlib framing.
There is no official public specification from Gravity; the format was reverse-engineered by the community and documented in the RagnarokFileFormats repository on GitHub. A PHP conversion class for .ebm ↔ .bmp is available on PHPClasses. The format has remained unchanged since the 2002 initial release.
Security & safety
RISK: LOWEBM files are compressed bitmap images; they contain no executable code. Risk limited to malformed zlib data causing a crash in a naive parser.
Format details
in a nutshellPrograms that open EBM files
Windows2 apps
Ragnarok Online
Freemium EBM files are used internally by the game client. Guild emblems are managed through the in-game guild UI; no manual opening needed for gameplay.
Custom zlib tool / EBM2BMP (PHP)
Open-source Use the PHP EBM2BMP library or any zlib inflate utility to decompress the EBM to a BMP for viewing in any image editor. Technical details
deep spec| Compression | DEFLATE via zlib; ~20% of files include a standard zlib header (`78 9C` / `78 DA`); remainder use raw DEFLATE stream without wrapper |
| Uncompressed content | Windows BMP bitmap, 24×24 pixels, 8-bit (256-colour indexed palette) |
| Fixed image dimensions | 24×24 pixels (all guild emblems use this exact size) |
| Colour depth | 8 bpp (256-colour indexed palette) |
| Uncompressed file size | 1,734 bytes (standard 24×24 8-bit Windows BMP) |
| Typical compressed size | 1 KB - 5 KB |
| Byte order | Little-endian (inherited from Windows BMP structure) |
| Checksum | Adler-32 - present only when standard zlib wrapper is used |
| Magic bytes | None fixed; `78 9C` or `78 DA` when zlib header is present; raw DEFLATE stream otherwise |
| Storage path | `/emblem/` directory in the Ragnarok Online client installation |
| Specification source | Community reverse-engineered; documented in RagnarokFileFormats on GitHub |
| Released | 2002 (Ragnarok Online initial release) |
| Specification | github.com |
EBM conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about EBM files.
