BMP

Windows Bitmap (Legacy Windows MIME Alias)

image/x-windows-bmp Released 1985 · by Microsoft Corporation

The image/x-windows-bmp MIME type is another legacy, vendor-specific alias for the Windows Bitmap (BMP) format. Highly similar to 'image/x-ms-bmp' and 'image/x-win-bmp', this variant was frequently utilized by older Windows desktop applications, legacy web servers, and MIME configuration tables to identify uncompressed Device-Independent Bitmaps (DIB). The underlying file is structurally identical to standard BMP files, featuring the classic 'BM' magic header and storing uncompressed, lossless pixel data.

Raster Graphics Transparency Production Ready

Technical Specifications

MIME Type

image/x-windows-bmp

Extensions

.bmp.dib

Container

DIB (Device-Independent Bitmap)

Compression

Uncompressed & Run-Length Encoding (RLE)

Algorithms

NoneRLE4RLE8

Color Depth

1-bit (Monochrome), 4-bit (16 colors), 8-bit (256 colors), 16-bit (High Color), 24-bit (True Color), 32-bit (True Color with Alpha)

Metadata

ICC

Capabilities

Transparency

Animation

Progressive Loading

Alpha Channel

HDR Support

Official Specification

Aliases: image/bmpimage/x-ms-bmpimage/x-win-bmpimage/x-bmp

Magic Bytes & HTTP Headers

File Signature (Magic Bytes)

42 4D

ASCII: BM

HTTP Headers

Content-Type: image/bmp

Content-Type: image/x-windows-bmp

HTML Accept Attribute

accept="image/bmp, image/x-windows-bmp, .bmp"

Browser Support Matrix

Browser	Status	Min Version
Chrome	Supported	1
Firefox	Supported	1
Safari	Supported	1
Edge	Supported	12
Internet Explorer	Supported	Legacy

Advantages & Limitations

Advantages

Universally supported by all major operating systems and modern web browsers
Maintains perfect, lossless fidelity because pixel data is stored without lossy compression artifacts

Limitations

Massive file size overhead due to a lack of modern compression algorithms
Legacy MIME strings like 'image/x-windows-bmp' can trigger validation warnings in strict security or API environments if unhandled

Developer Code Snippets

import magic
# Modern Libmagic resolves BMP files to the standard 'image/bmp'
print(magic.from_file('image.bmp', mime=True)) # Outputs 'image/bmp'

const mime = require('mime');
console.log(mime.getType('image.bmp')); // Outputs 'image/bmp'

import (
    "bytes"
    "net/http"
)
// Native Go HTTP detection reads the 'BM' header and returns 'image/bmp'

// Example of normalizing legacy MIME types during file uploads
$mime = $_FILES['upload']['type'];
if (in_array($mime, ['image/x-windows-bmp', 'image/x-win-bmp', 'image/x-ms-bmp'])) {
    $mime = 'image/bmp';
}
echo $mime;

File Detection Steps

How to programmatically detect a image/x-windows-bmp file by reading its raw bytes:

1 Check the first two bytes of the file for the ASCII string 'BM' (Hex: 42 4D). This is the definitive signature for a Windows Bitmap.
2 The 'image/x-windows-bmp' string exists purely on the protocol/MIME layer and does not alter the underlying binary structure of the file.

Software Support

M

Microsoft Paint

A

Adobe Photoshop

GIMP

ImageMagick

Conversion Tools

Share & Embed

Markdown Badge

[![BMP Format](https://freewebptojpg.com/mime/image/bmp/badge.svg)](https://freewebptojpg.com/mime/image/bmp)

Interactive iframe Widget

<iframe src="https://freewebptojpg.com/mime/image/bmp/embed" width="100%" height="280" style="border:1px solid #cbd5e1;border-radius:8px;" title="BMP Specs"></iframe>

JSON API

All data on this page is available as a free, open JSON API. Use it in your project, documentation, or tooling.

GET https://freewebptojpg.com/mime/image/bmp.json Open JSON

Free to use

No auth required

CORS enabled

Use from any domain

Cached 24h

Cache-Control headers set

Frequently Asked Questions

What is the difference between image/x-windows-bmp and image/bmp?

There is no difference in the actual image file. 'image/bmp' is the official IANA standard. 'image/x-windows-bmp' is an older vendor alias historically assigned by specific Windows environments or legacy application registries when handling .bmp files.

How should I handle image/x-windows-bmp in backend file uploads?

When accepting file uploads, if your server encounters legacy strings like 'image/x-windows-bmp', 'image/x-ms-bmp', or 'image/x-win-bmp', you should write normalization logic to map them to the standard 'image/bmp' format in your application database.

Should I serve BMP files on modern websites?

No. While modern web browsers support rendering BMP files, their massive, uncompressed file sizes lead to poor page performance. You should convert them to WebP, AVIF, or PNG before web deployment.