From SIN­GLE cli ck to FIN­ISHED im­age

You press the but­ton, but then a whole se­quence of events takes place inside your cam­era

NPhoto - - Nikopedia -

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.

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