Since RED first introduced the RED One 35mm cinema camera in 2006 eventually we learned about its powerful 12-bit RAW format. Today more and more cameras including; BMC, FS700, F5/F55/F65, C500, ikonshkop, and D16 (in development) are capable of recording data directly off the sensor and storing the RAW data.

“RAW” gets a lot of credibility for its ability to contain “more information” but it has much more to do with the fact that when shooting RAW photos with DSLR’s or RAW video with camera like RED, the signals are stored using a linear gamma. i.e. data directly off the sensor which is linear based. Later in post processing once gamma correction is applied to match how we perceive light (more logarithmically) the data which represents the entire tonal range becomes skewed and biased towards the bright tones. So “more information” in this case is really only available in the bright tones and not so much the middle or dark tones.

Probably everyone has heard someone say when using a histogram keep the hill to the right. With linear based encoding there is good reason for that since you will use more of the data bits available to represent the overall image. Example:

Original scene:

What the sensor sees and how a linear signal looks using 5-bit representation (32-steps):

Gamma correction applied to same linear signal so we can view it:

(note the increased levels in the bright tones)

Not all RAWs are equal either. ARRIRAW shoots RAW but uses LOG to encode the signal. BMC is also doing something similar to LOG, and the new F5/F55 is not very clear to me yet but judging from Ben Allen’s latest article which indicated log is being applied in post processing, it leads me to believe Sony RAW is also perhaps using linear gamma to encode the information and later in post curves are applied.

So what is RAW really? A format that contains unaltered Bayer sensor information – but how it is encoded (ie. log or linear gamma) makes all the difference and becomes especially important for knowing how to handle exposure not only on different cameras but the overall and complete format itself being used.