X3F to SK Converter

X3F is the proprietary RAW image format used by Sigma cameras equipped with Foveon X3 direct image sensors, introduced in 2002 with the Sigma SD9 — the first digital SLR camera to use a sensor that captures full color information at every pixel location. Unlike conventional cameras that use a Bayer color filter array (where each pixel records only one color and the other two are interpolated), the Foveon X3 sensor stacks three photodiode layers at each pixel site, exploiting silicon's wavelength-dependent absorption depth to capture blue, green, and red light simultaneously. X3F files therefore store a fundamentally different kind of raw data: three complete color planes captured at the same spatial location, with no demosaicing required. The format uses a proprietary container with multiple data sections including the raw sensor data (compressed using a Huffman-based scheme), embedded JPEG previews, camera metadata, and Sigma-specific processing parameters. One advantage is the absence of demosaicing artifacts: because every pixel records all three colors natively, X3F images exhibit a per-pixel sharpness and color accuracy that Bayer-based sensors achieve only after interpolation — there is no moire, no false color, and no loss of spatial resolution from the color reconstruction step. This produces a rendering quality that many photographers describe as uniquely three-dimensional and film-like, particularly at low ISO settings. X3F files can be processed using Sigma's Photo Pro software, and are also supported by dcraw, Iridient Developer, and other RAW converters.