Raw image formats are intended to capture the radiometric characteristics of the scene, that is, physical information about the light intensity and color of the scene, at the best of the camera sensor's performance. The purpose of raw image formats is to save, with minimum loss of information, data obtained from the sensor.
Unlike physical film after development, the Raw file preserves the information captured at the time of exposure. Like undeveloped photographic film, a raw digital image may have a wider dynamic range or color gamut than the developed film or print. (With exposed film, development is a single event that physically transforms the unexposed film irreversibly.) Rather, the Raw datasets are more like exposed but undeveloped film which can be converted (electronically developed) in a non-destructive manner multiple times in observable, reversible steps to reach a visually desired image. Raw image files are sometimes incorrectly described as 'digital negatives', but neither are they negatives nor do the unprocessed files constitute visible images.
