Having just finished 3 workshops at Cinegear and a full day F5/F55 workshop at AbelCine one thing became apparent. There is a lot of confusion over raw and log recording. I overheard many people talking about shooting raw using S-log2/Slog3 or people simply interchanging raw and log as though they are the same thing.
Raw and Log are completely different things!
Generally what is being talked about is either Raw recording or recording using a log format such as S-Log2/S-log3 using component or RGB full colour video. Raw simply records the raw, image data coming off the video sensor, it’s not even a color picture as we know it. It is just the brightness information each pixel on the sensor captures with each pixel sitting beneath a colour filter. It is an image bitmap, but to be able to see a full colour image it will need further extensive processing. This processing is normally done in post production and is called “de-bayering” or “de-mosaicing” and is a necessary step to make the raw useable.
S-Log, S-Log2/3, LogC or C-Log is a signal created by taking the same sensor output as above, then processing it in to an RGB or YCbCr signal by de-mosiacing in camera and then applying a log gamma curve. It is conventional video but instead of using a “normal” gamma curve such as Rec-709 it uses an alternate gamma and just like any other conventional video format it is full colour. S-Log and other log gammas can be recorded using a compressed codec or uncompressed, but even when uncompressed, it is still not raw, it is component or RGB video.
So why the confusion?
Well, if you tried to view the raw signal from a camera shooting raw in the viewfinder without processing it, it would not be a colour image and it would have a very strange brightness range. This would be impossible to use for framing and exposure. To get around this a raw camera will convert the raw sensor output to conventional video for monitoring. Sony’s cameras will convert the raw to S-Log2/3 for monitoring as only S-Log2/3 can show the cameras full dynamic range. At the same time the camera may be able to record this S-Log2/3 signal to the internal recording media. But the raw recorded by the camera on the AXS cards or external recorder is still just raw, nothing else.
UPDATE: Correction/Clarification. There is room for more confusion as I have been reminded that ArriRaw as well as the latest versions of ProResRaw use Log encoding to compact the raw data and record it in a more efficient way. It is also likely that Sony’s raw uses data reduction for the higher stops via floating point math or similar (as Sony’s raw is ACES compliant it possibly uses data rounding for the higher stops).
ArriRaw uses log encoding for the raw data to minimise data wastage and to squeeze a large dynamic range into just 12 bits, but the data is still unencoded data, it has not been encoded into RGB or YCbCr. To become a useable colour image it will need to be de-bayered in post production. Sony’s S-Log, S-Log2/3 Arri’s LogC, Canon’s C-Log as well as Cineon are all encoded and processed RGB or YCbCr video.