From SINGLE cli ck to FINISHED image
You press the button, but then a whole sequence of events takes place inside your camera
01 Demosaicing Something called a Bayer filter array sits in front of the sensor, and each of its pixel-sized filters are coloured either red, green or blue. This is how the otherwise colour-blind sensor records colours, and this blocky patchwork of colours in the image has to be processed to resemble the original colours in the scene. This is processing-intensive and better tackled by a computer – in fact, the best demosaicing procedures are iterative (meaning lots of computations performed repeatedly) and these are too slow for a camera’s processor. Software engineers at Adobe, DxO and other firms put a lot of effort into getting this right.
02 White balance The overall colour is adjusted according to the choice selected on the camera. For reasons which are too complex to go into here, Bayer filters feature twice as many green filters as red and blue ones, which adds a green cast that needs to be removed. The white balance setting chosen from the camera menu is kept as a tag which, if the RAW file is saved for later processing, you can change.
03 Apply gamma curve The sensor records light in proportion to the exposure – that is, in a linear way. Our eyes are more complex. They have a logarithmic response, which essentially means that they can sense a much wider range of brightness at the same time. An original linear image looks too dark to the eye, and to appear normal needs to have a strong adjustment curve applied to it, known as a 2.2 gamma curve (see below). This effectively expands the darker pixel levels into a wider range of tones, and squashes the brighter pixel levels.
04 Tidying up Various other jobs include applying some sharpening to take care of the slight softening caused by demosaicing, and adjusting the contrast and saturation.
05 Convert or save Finally, if you chose to shoot in JPEG, the file is now converted by the camera, with all other data discarded. If you chose to shoot in RAW, everything is kept, and the various processing steps can be revisited.