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 or people simply interchanging raw and log as though they are the same thing.
Raw and Log are completely different things!
Raw simply records the raw, unprocessed data coming off the video sensor, it’s not even a color picture as we know it, it does not have a white balance, it is just digital “1’s” and zeros coming straight from the sensor.
S-Log, S-Log2, LogC or C-Log is a signal created by taking the sensors output, processing it in to an RGB or YCbCr signal and then applying a log gamma curve. It is much closer to conventional video, in fact it’s actually very similar, like conventional video it has a white balance and is encoded into colour. S-Log etc can be recorded using a compressed codec or uncompressed, but even when uncompressed, it is still not raw.
So why the confusion?
Well, if you tried to view the raw signal from a camera shooting raw in the viewfinder it would look incredibly dark with just a few small bright spots. This would be impossible to use for framing and exposure. To get around this a raw camera will convert the raw sensor data to conventional video for monitoring. Many cameras including the Sony F5 and F55 will convert the raw to S-Log2 for monitoring as only S-Log2 can show the cameras full dynamic range. At the same time the F5/F55 can record this S-Log2 signal to the internal SxS cards. But the raw recorded on the AXS cards is still just raw, nothing else, the internal recordings are conventional video with S-Log2 gamma (or an alternate gamma if a look up table has been used). The two are completely separate and different things and should not be confused.
UPDATE: Correction/Clarification. OK, there is room for more confusion as I have been reminded that ArriRaw uses Log encoding. 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 and it does not have a white balance or have gain applied, all of this is added in post. Sony’s S-Log, S-Log2, Arri’s LogC, Canon’s C-Log as well as Cineon are all encoded and processed RGB or YCbCr video with a set white balance and with a Log gamma curve applied.