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What is a RAW File?

A RAW file contains minimally processed measurements from a camera sensor plus metadata needed to interpret them. It is not a single universal layout, and camera vendors may use different formats.

How RAW Files work

A camera RAW file packages sensor-derived samples with the calibration and capture metadata required to turn them into a viewable image. For color-filter-array sensors, development includes black-level correction, demosaicing, white balance, color transformation, and tone mapping, each of which can change the rendered result. Sensors that capture every color component at each pixel, such as Sigma’s Foveon, skip demosaicing but still need the other steps. Most RAW formats are proprietary and sparsely documented; Adobe’s Digital Negative (DNG) is a publicly documented, TIFF-based alternative that cameras can write directly or that files can be converted to. RAW therefore functions as a source master in an imaging workflow, while previews and standardized exports serve selection, editing interchange, and delivery.

Key facts

  1. RAW does not mean uncompressed, or even lossless. The Library of Congress notes that some RAW formats leave the camera compressed, and Adobe’s DNG specification defines lossy JPEG and JPEG XL options alongside lossless ones. Decoders can lag behind these modes: darktable’s camera support page lists Fujifilm lossy RAF, Nikon high efficiency NEF, and DNG 1.7 with JPEG XL among formats it explicitly does not support. Check the compression mode as well as the file extension.
  2. The preview embedded in a RAW file is a separate image that was already rendered, by the camera or by the software that wrote the file, not a view of the sensor data. LibRaw hands back a JPEG thumbnail exactly as stored, the DNG specification records which application created each preview, and darktable’s manual explains that a fresh conversion often looks flatter and less saturated than the in-camera JPEG because that processing has not been applied. Judge a pipeline by its own conversions, not by the preview.
  3. Proprietary RAW decoding is tied to camera models, not just to file extensions. Adobe’s DNG specification says software must have specific information about the camera that created a proprietary file and must be updated as new models appear, and LibRaw publishes its supported cameras per release. A decoder that reads last year’s files from a brand can therefore fail on a newer body that uses the same extension. There is no single date when a model becomes supported: LibRaw says it has no control over which LibRaw version other software uses and refers users to their software vendor.
  4. DNG reduces that dependence but is optional. The specification requires black-level information in the file so that readers need not work out each camera model’s black levels, though not every decoder reads every DNG variant (see darktable’s list above). The Library of Congress describes DNG as a way to mitigate the risk that a proprietary format loses support, noting that a DNG can also contain a copy of the original file. The Library still accepts camera RAW formats for digital photographs, so converting is a preservation choice, not a requirement.

When RAW Files matter

Retain RAW input when an imaging workflow needs greater latitude over demosaicing, exposure, dynamic range, or color. Distribution requires development into a broadly supported format, and decoder compatibility varies by camera.

How Transloadit helps with RAW Files

Transloadit’s image formats table, which applies to /image/resize, /image/enhance, and /document/thumbs, lists camera RAW formats such as ARW, CR2, CR3, DNG, NEF, ORF, and PEF as readable but not writable on both listed ImageMagick stacks, so a RAW upload can be the input for conversion to a delivery format.

The table lists formats per stack, not camera models or compression modes, and it does not describe how the conversion is rendered. Test with files from the cameras you need to support.

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