Raw Images
Raw image files are so named because they are the un-processed image files generated by digital cameras, image scanners and motion picture film scanners. Raw files are not yet in a form in which they can be digitally edited, transformed and printed. If you’ve researched the different cameras for sale, and have (correctly) settled upon a digital camera, then the information on this page might prove useful.
Comparisons are often made, conceptually at least, between raw files and the “negatives” that a roll of film transforms into after chemical processing. This parallel relies on the fact that both, raw file formats and film negatives, contain all the information necessary to create an image, but are not usable as images themselves. Raw images must, therefore, be converted into “positive” formats. The positives that raw files transform into are the raster formats discussed elsewhere on this website: e.g. JPEG, TIFF, BMP, etc.
The conversion process is performed by a raw converter in a wide-gamut internal colourspace where precise adjustments can be made before the file’s final transformation into a positive file format. The raster file can then be edited, printed and stored. In a reference to the comparisons made between digital and analogue processes, raw file conversion is often referred to as “developing”.
Numerous raw file formats are currently used by different camera and scanner manufacturers, although there are current debates centred on the implementation of a standard raw file format. General opinion seems to suggest that the Adobe DNG (Adobe Digital Negative) file is a favourite candidate for the standard format.
Raw files are larger than compressed raster formats as they contain as much information about an image as is possible. The size of the file is ultimately dependent on the quality and size of the sensors used to collect visual data. In the case of digital cameras, the amount of photo-receptive elements (pixels) built into the sensor directly translates into the quantity of data recorded by the raw file. In addition to the digitisation of light and colour, raw files also record metadata (time, place and filename information) which is attached to each photo. Most digital cameras have a file conversion programme on-board, allowing the user to preview an image on a liquid crystal display (LCD) screen.
Raw files represent the endeavour of camera and scanner technology producers to save as much data captured by the sensor as is possible, keeping loss to an absolute minimum. The unprocessed data needs to be developed into a positive before it can be seen as usable digital data. In this light, the raw file is an essential link in the chain of processes whereby light is transformed into digital binary sequences. For general end user needs, raw files will very rarely ever be worked with: that is, for most editing purposes, raster files are more than adequately equipped to produce pleasing results. If the user is familiar with raw files and their characteristics, working with the format can be beneficial: raw files are considered as a lossless format, which means that although file sizes are larger than compressed files, the format retains more data received from the sensor. This in turn allows for greater control when fine tuning an image: raw conversion software allows users to manipulate a larger quantity of parameters than compressed formats (e.g. brightness, hue, saturation, intensity, colour balance, white balance and contrast). The latter parameters are also editable in raster formats, but with a lesser degree of accuracy. A final advantage of raw files is that they have 12- or 14-bits of intensity information, which is a higher amount of data than the compressed 8-bits stored by JPEG files.