Overview
Introduction
This tool converts a JPG or JPEG image into a genuine uncompressed BMP file, entirely in your browser, using a hand-written encoder that writes the exact byte layout Windows and most image editors expect.
Because a decoded JPEG is always fully opaque, the output uses a compact 24-bit format rather than carrying an unnecessary alpha channel.
What Is JPG to BMP Converter?
A client-side JPG-to-BMP converter that decodes an uploaded JPEG into raw pixel data, then writes a 14-byte BITMAPFILEHEADER followed by a 40-byte BITMAPINFOHEADER and the pixel data itself, in the bottom-up, BGR, 4-byte-row-padded layout the BMP spec requires.
No compression is applied at any point; that's inherent to classic BMP, not a limitation of this tool specifically.
How JPG to BMP Converter Works
After the browser decodes the JPEG into RGBA pixels, the encoder computes the padded row size BMP requires (each row rounded up to a multiple of 4 bytes), then writes pixel rows from bottom to top with each pixel's blue, green, and red bytes in that order.
The file and info headers are filled in with the image's dimensions, a 24-bit depth, and BI_RGB (uncompressed) as the compression method, producing a file that any standard BMP reader can open.
When To Use JPG to BMP Converter
Use it when a legacy tool, embedded device, or specific workflow requires an uncompressed BMP rather than a compressed format like JPEG.
It's also useful for testing or teaching purposes, since BMP's simple layout makes it easy to inspect pixel data directly in a hex editor.
Often used alongside BMP to JPG Converter, PNG to BMP Converter and JPG to GIF Converter.
Features
Advantages
- Runs entirely client-side; your image is never uploaded to a server.
- Writes a genuinely valid, widely-compatible 24-bit uncompressed BMP file.
- Keeps the file smaller than it would be with an unnecessary 32-bit alpha channel, since JPEG source images are always opaque.
Limitations
- Output files are much larger than the source JPEG, since BMP here is uncompressed.
- Only 24-bit output is produced; there's no option for 8-bit indexed BMP output.
Examples
Best Practices & Notes
Best Practices
- Only convert to BMP when a specific tool or workflow actually requires it; for general use, JPEG or PNG will almost always be a better fit.
- Expect file sizes several times larger than the source JPEG and plan storage accordingly.
Developer Notes
convertJpgToBmp writes a classic BITMAPINFOHEADER instead of the BITMAPV4HEADER this site's PNG-to-BMP encoder uses, since a decoded JPEG has no alpha channel to preserve: a plain 24-bit encoding is smaller and just as widely compatible without an unused alpha bitmask.
JPG to BMP Converter Use Cases
- Producing an uncompressed BMP for a legacy application or embedded device
- Teaching or demonstrating raw bitmap file structure
- Feeding a tool that specifically expects BMP rather than a compressed format
Common Mistakes
- Being surprised by how much larger the BMP is than the source JPEG; that's expected for an uncompressed format.
- Assuming BMP will preserve transparency; a JPEG source has none to begin with.
Tips
- If file size matters, keep the JPEG and only convert to BMP for the specific tool that needs it.
- Use a hex editor on the output if you want to see BMP's header fields directly; the format is simple enough to read by hand.