Camera RAW refers to data captured by the sensor of a digital camera via a Colour Filter Array. It is popular convention to write camera ‘RAW’ in capitals but it isn’t an acronym as far as I am aware, it is just the word ‘raw’ to denote data in a raw format as opposed to data that has been processed.

As you may already know a colour filter is a semi-transparent medium that only allows light of a certain frequency to pass through it. In simpler terms a red filter for example would only allow red light to pass through, that is light that we as humans ‘see’ as the colour red.

An array, as you might also be aware is a collection of things, in this case a grouping of tiny colour filters arranged in a grid pattern, perhaps we could imagine it to be a little like a chess board, although some manufacturers Fuji for example, have produced more exotic shapes.

The camera sensor itself is an array of small light sensitive diodes - small electrical components that allow a variable level of electrical current to flow through them depending on the level of light hitting them. So the Colour Filter Array sorts out light into seperate frequencies (colours) and the light sensor measures the level of light (brightness) passing through each area of the colour filter.

Colour Filter Arrays are typically in the form of a Bayer Pattern of alternating areas of red, green and blue colour filters, with 50% green squares and 25% red and blue respectively. This is similar to the ratio of red, green and blue colour sensitive cells in the human eye. Some models of camera use other patterns in alternating grid arrays.

So the camera RAW data itself is an array or collection of luminance (brightness) values of seperate frequencies (colours) of light on seperate areas of the light sensor of the camera. This is fundamentally different to the data found in a typical bitmap image that we might view on a monitor which is an array of values representing values of colour of red, green and blue together in each pixel area.