BMP to ORF Converter

Encoding: the BMP uses usually none; RLE for some 4 and 8-bit files; ORF uses losslessly compressed sensor data, with a preview and thumbnail, and the download is a Linear DNG: demosaiced 8-bit RGB with the colour matrices raw editors need.

Bit depth: 1, 4, 8, 16, 24 or 32 bits per pixel in the BMP; ORF allows 12 bits per channel, and the DNG written here has 8 bits per channel, linearised.

Colour: RGB or an indexed palette in the BMP; ORF supports camera RGB from a Bayer mosaic, written here as 8-bit sRGB.

Transparency: the BMP stores it as an optional fourth byte in 32-bit files, which many programs ignore; the DNG has none, so transparent areas are filled with the colour you choose.

Metadata: the BMP can carry nothing beyond the header's resolution fields (and a colour profile in rare V5 headers); ORF can carry EXIF and Olympus maker notes, which also contain the preview, but nothing is copied across.

BMP stores raw, uncompressed pixels. Files are huge but trivially simple, which is why some legacy Windows software, embedded displays and printers still ask for it.

A BMP is a 14-byte file header ('BM' and the offset to the pixels), a DIB header (40 bytes, or 108 and 124 bytes in the V4 and V5 versions that add colour masks and alpha), an optional palette, then pixel rows padded to 4 bytes and normally stored bottom-up.

BMP files usually come from Windows Paint, legacy Windows programs, embedded displays and some scanners.

ORF is the raw format of Olympus and OM System cameras, built around Four Thirds and Micro Four Thirds sensors. It stores 12-bit sensor data with a JPEG preview kept inside Olympus's maker notes.

ORF looks like TIFF but replaces the version number 42 with the letters 'RO', so a little-endian file starts 'IIRO' and generic TIFF readers reject it. Its JPEG preview is not in the main image directory but inside the camera-settings block of Olympus's maker notes.

ORF files come from Olympus E-series DSLRs, OM-D and PEN mirrorless cameras and OM System bodies.

Forms and workflows that ask for ORF usually feed a raw editor, and each of those opens DNG as well, so the DNG can take the ORF's place. Keep the BMP if you only need to view or share the picture.

What ORF offers when it comes straight from the camera: Compact files from a smaller Four Thirds sensor; High Res Shot results stored as a single file; Supported across two decades of Olympus and OM System bodies. Its drawbacks: An 'IIRO' header that generic TIFF readers reject; 12-bit depth, less than most full-frame raw files; A preview hidden inside the maker notes.