what is RAW

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What is RAW:

A RAW file is a Greyscale file and does not contain anything we humans can see as color as opposed to a TIFF or JEPEG which are ‘processed and contain the colour information required to view it.

The RAW file will also contain the interpretive 'information' (White Balance, Colorimetric interpretation, Gamma Correction, etc) and it is that which will be utilised by the camera or computer software converter to translate this data based on the characteristics of the color filter array (The sensor) 

Linear/Non Linear: 

Digital capture (with regard to Gamma; i.e. highlight to shadow contrast) requires encoding as it is linear (Gamma Value of 1) and records a linear response to incoming photons.

Film and the human eye have a Gamma response of between 2 & 3 and as such are able to perceive more precise changes in light. 

Eyeball Vs Sensor:

 If you double the output of a light source, we humans know it is brighter but we do not know it is twice as bright. For a digital sensor, it is quantifiable data as is actually twice as bright (Thus it is linear). 

The retina is able to compress non-linearity but a digital sensor cannot. (This is how we are able to go from darkness to bright light without burning our eyeballs. (Obviously we have the benefit of an iris as a camera has aperture adjustment)

Linear and Stops:

 For a 12 bit capture, 4,096 levels are available. And thus 2,048 represents half the number of photons recorded at level 4,096. (Linear).  

This relates to digital capture as follows. If a camera capture has 6 stops, half the 4,096 levels (2,048) are devoted to the brightest stop and half of that (1024) is devoted to the next stop down. And so on.
2,048 > 1,024 > 512 > 256 > 128 > 64

Thus, the final stop is only 64 levels and this represents extreme shadows and explains why digital is restricted in shadow recovery but good in highlight recovery.

Digital Exposure:

It is a common misconception that with digital you should underexpose to avoid blowing highlights but as shown, there are fewer levels (64) down there and you can run the risk of lack of detail in the shadows and introducing noise.

Exposure for digital is as important as in film. With digital, exposure must be as close as possible to ‘blowing’ the highlights without actually losing that detail.