JPG to BMP Converter

BMP is the uncompressed Windows bitmap that older programs, embedded displays, label and card printers, embroidery machines and many hobby electronics projects require. This converter decodes each JPG in your browser — turning it upright according to its EXIF orientation, as phones expect — and writes a standard 24-bit BMP, or an 8-bit greyscale BMP when the target only needs shades of grey.

How to use this tool

1. Drop one or more JPG or JPEG photos.
2. Choose 24-bit colour, or 8-bit greyscale for a third of the size.
3. Optionally set the DPI to store and a max size (BMP files get large).
4. Download each BMP, or all of them as a ZIP.

Formula

BMP size = 54 bytes of headers + height × row, where row = width × 3 bytes rounded up to a multiple of 4 (24-bit). 8-bit greyscale: 1,078 bytes of headers and palette + height × (width rounded up to a multiple of 4).

Rows are stored bottom-up in blue-green-red order with BI_RGB (no compression). Greyscale uses the Rec. 601 weights 0.299 R + 0.587 G + 0.114 B, the same luma JPEG itself uses. The DPI is written as pixels per metre; "Keep" uses the JPEG's JFIF or EXIF resolution and 96 DPI when it has none.

Example

A 4000 × 3000 photo has rows of 12,000 bytes, so the 24-bit BMP is 54 + 3000 × 12,000 = 36,000,054 bytes (about 34.3 MB). As 8-bit greyscale it is 1,078 + 3000 × 4,000 = 12,001,078 bytes. With a max size of 1600 px the colour BMP shrinks to 1600 × 1200 and 5,760,054 bytes.