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A raw image file is one used by certain digital cameras, which saves all pixels of the digital sensor without changing the light and colour conditions captured by the lens. All settings by the photographer, like white balance, color saturation, and others are ignored. So, if the picture is taken with an image quality of, for example, 5 million pixels (5 mega pixels), the raw file will be of 5 million pixels, too, and consequently of 3×5=15 million bytes (assuming a 3-component, 8 bits/components color space, for example a 24 bit RGB representation). One standard file format in digital cameras is the JPEG file, which compresses the data of the sensor, thus allowing for much more pictures to be stored in the memory card than in the case of the raw files. In exchange, the quality of the image suffers to a certain extent.
Because of the large amount of memory they need, raw files are used when a high image quality is required and, what is more important, when the image is intended to be processed afterwards on a computer.
The cameras which allow saving images in raw format offer this option in addition to the JPEG file format, which - as said - is a standard in digital photography.
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