ICO to ORF Converter

Encoding: the ICO uses each size stored as a headerless BMP or as a complete PNG; 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 to 32 bits per pixel, set per size in the ICO; ORF allows 12 bits per channel, and the DNG written here has 8 bits per channel, linearised.

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

Transparency: the ICO stores it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons; the DNG has none, so transparent areas are filled with the colour you choose.

Other images: the ICO can hold several sizes of the same picture, typically 16, 32, 48 and 256 px; only the main image is converted.

Metadata: the ICO can carry only a directory of the sizes inside, with no EXIF; ORF can carry EXIF and Olympus maker notes, which also contain the preview, but nothing is copied across.

ICO is a container that bundles several sizes of the same icon (16, 32, 48, 256 px) into one file. It is still the most compatible format for website favicons and Windows app icons.

An ICO starts with a 6-byte ICONDIR (type 1 for icons) and a 16-byte entry per image giving width, height, colour count and offset. Each image is either a BMP without its file header plus an AND mask, or a complete PNG.

ICO files usually come from website favicons, Windows programs and installers.

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 ICO 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.