One of the key benefits of a raw workflow is that normally you will be working at a higher bit depth, at least 12 bit if not 14 bit or 16 bit. This in turn allows the use of linear capture as opposed to the log capture normally associated with conventional video.
Don’t get me wrong, log capture and recording (even things like hypergammas and cinegammas are closer to log than linear) is very good and works remarkably well. But it is limited as it compresses highlight information. Each extra stop of over exposure with a linear recording will contain twice as much data as the previous, while with log each stop contains the same amount of data, so as a result each brighter stop only has half as much information as the previous. Log does allow us great scope when it comes to grading and post production image manipulation, but the higher up the exposure range you go, the less data you have to work with, so how much you can manipulate the image decreases with brightness. As our own visual system is tuned for mid tones this log behaviour goes largely un-noticed. But as modern sensors achieve greater and greater dynamic ranges log starts to struggle while linear copes much better.
It’s not until you try linear raw with a camera like the Alexa or F65 that you realise just how forgiving it is. In log mode the Alexa (and other log cameras like the F3) need to be exposed accurately. Over expose and you risk not only your highlights blowing out but also it becomes harder to get good looking skin tones as these may be up in the more compressed parts of the curve. However with linear, it doesn’t really matter if faces are higher up the range, jus as long as they are not actually at sensor overload.
When you shoot with a log camera it must be treated like any other conventional video camera. Exposure must be correct, you need to watch and protect you highlights, expose to the left etc. A camera shooting raw behaves much more like a film camera, you can afford to push the exposure higher if you want less noise, just like film.
But linear raw comes at a cost, mainly a time and storage cost. We have become very used to the simplicity of working with video. Modern file based workflows are fast and efficient. Raw needs more work, more processing, more storage (compared to compressed at least). But computers are getting faster, storage is getting cheaper. Right now I believe that raw is only going to be used by those that really do need and want the very best flexibility in post production while log will become more and more common for episodic and documentary production. But, the time will come when we can handle raw quickly and easily and then perhaps we will look back at legacy codecs and wonder how we managed. Although saying that, while we still broadcast and distribute programmes using backwards compatible legacy gamma with it restricted dynamic range for display on devices with only 6 stops of display latitude, a general shift to raw with all it’s extra overheads may never happen.
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