Make sense of sensors

Understanding how camera sensors work can help you get a better tonal range in your images

Digital images are created from millions of individual pixels, created by sophisticated processing by the EXPEED processor within your Nikon camera. Turning the image you want to shoot into a digital version is a complex process and understanding a little bit about this process will help you set up your camera to record a wider dynamic range and tonality in your shots. The camera’s sensor is made up of light-sensitive cells, known as photosites. Each photosite is tiny; approximately 0.004mm across. They create an electrical signal in proportion to brightness that they receive through the lens from a given part of a shot. Photosites only see luminance, not colour. To produce a colour image, each photo site has a mini coloured filter across it, either red, green or blue. This is known as a Bayer Array. A photosite with a green filter will only see colours that have some green light in them, likewise for the colours on the other photosites. As practically all colours can be created by mixing red, green and blue (RGB) light together, the photosites work together to create the pixel colours we see in our images. For example, a photosite with a green filter can effectively see ‘blue’ light by using information from the neighbouring blue and red filtered photosites. This process is known as demosaicing. When your camera is set to JPEG, each photosite can register 8 bits of data, which means that you get 256 shades of brightness. Raw files take this tonality to another level. 12-bit Raw files give you 4,096 shades of brightness, while with 14-bit Raw files a staggering 16,384 levels of brightness can be recorded per pixel. For JPEGS, when you combine the shades of brightness with the colour information from the demosaicing process you get somewhere in the region of 16.7 million possible colours. Raw files, on the other hand, will show many more colours and a wider brightness range (dynamic range), and therefore much smoother tonal graduations between each different shade of colour in your images.