Early remote sensing devices recorded photographic images on film (taken by cameras) or traces printed onto paper rolls (sonar devices). Both routes created an image in analogue format. These images were fixed and could not be subject to very much manipulation (correction, change of contrast or colour etc); more recently, they can be converted into an electronic digital format for limited manipulation. Most modern sensors now record their information in digital format, often as digital images. A digital image is made up of numbers, which represent image attributes such as brightness, colour or radiated energy frequency wavelength, and position location for each point or picture element in the image. The smallest sized picture element on an image is called a pixel; a digital image is made up of pixels arranged in rows and columns commonly known as a raster image. The dimensions and the information content of these pixels are both aspects of the resolution of the image.