Check if Image is BMP Online
Check if Image is BMP and Verify whether a file is a BMP image by reading its magic bytes and header. Detects V2, V3, V4, V5, plus OS/2 variants.
Drop a file in and get a byte-level verdict: BMP or not, with the exact header version (V2–V5) and OS/2 variants detected from the magic bytes.
Click to upload or drag and drop
Any file — the tool reads the first 256 bytes locally, regardless of extension
Details
First 14 bytes (hex)
A BMP always starts with 42 4D (ASCII BM). OS/2 bitmap arrays may start with BA, CI, CP, IC, or PT.
How to Use Check if Image is BMP Online
- Drop any file on the upload area - the tool ignores the extension and inspects the actual bytes. Only the first 256 bytes are read, so even gigabyte files open instantly.
- Read the verdict: the big green panel says "BMP" with the header version (V2, V3, V4, or V5), or the amber panel says "Not a BMP" with the specific reason.
- Scan the details card: file name, size, reported MIME, magic-byte label, header size, dimensions, bit depth, compression, colours used, and whether it's a top-down DIB.
- Inspect the hex line: the first 14 bytes in uppercase hex so you can cross-check against a reference or a hex editor.
- Press
Ctrl+Enter(⌘+Enteron Mac) to re-run the check on the last file - useful if you suspect a write locked it. - Copy the full report to your clipboard or Download a timestamped `.txt` file naming the original filename for archiving.
Frequently asked questions
Is my file uploaded anywhere?
No. The check runs entirely in your browser. Only the first 256 bytes are read – with File.slice().arrayBuffer() – so even huge files are never fully loaded or transferred.
How is the BMP format detected?
The tool reads the first two bytes and looks for 42 4D (ASCII BM). OS/2 bitmap-array variants (BA, CI, CP, IC, PT) are also recognised and labelled.
Does it detect a BMP renamed to .jpg?
Yes. The extension is ignored – only the magic bytes matter. A BMP file saved as logo.jpg is still reported as BMP.
What if a file has a .bmp extension but isn’t BMP?
It’s reported as “Not a BMP” with the reason “Magic bytes X do not match”. The extension is unreliable – always trust the bytes.
Which BMP header versions are recognised?
BITMAPCOREHEADER (V2, 12 bytes), BITMAPINFOHEADER (V3, 40 bytes), BITMAPV4HEADER (108 bytes), and BITMAPV5HEADER (124 bytes). Other header sizes are still labelled as “BMP” with the size shown so you can research further.
What does the bit depth field mean?
The number of bits per pixel: 1 (monochrome), 4 (16-colour), 8 (256-colour), 16 (5-5-5 or 5-6-5), 24 (RGB888), or 32 (RGBA8888). Combined with compression, this describes the pixel storage format.
What is a top-down DIB?
Most BMP files store rows bottom-up, which is why the height field is positive. A negative height flags the file as top-down – rows read from first to last line. The tool shows this with a “Top-down DIB” row.
Why does my BMP file show a “Bitfields” compression?
BITMAPINFOHEADER supports BI_BITFIELDS (code 3) which explicitly sets the red/green/blue masks. It is common for 16-bit and 32-bit BMPs. The pixel data is still uncompressed; only the channel layout is custom.
Is there a file size limit?
No. Only the first 256 bytes are read, so file size is irrelevant for the check itself.
Does it work offline?
After the page loads, yes. HTML, CSS, and JS are self-contained, so you can disconnect Wi-Fi and keep checking files.