SimonMW
lvl.2
Flight distance : 361263 ft
United Kingdom
Offline
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ge0se already answered for me. You get maximum tonal range by using the default gamma, not the log gamma.
Look at it like this. With an 8-bit colour system like you have on the Inspire 1 recordings, you have 256 graduations of each colour. By using a log gamma you are trying to compress the full DR range of the sensor into a small bit-space by re-allocating and prioritising certain areas of the brightness curve. One particular area that this causes problems in is highlights and shadows, which are at a lot of risk of banding issues in 8-bit colourspace due to tonal compression, since the log gamma curve allocates less of the brightness curve to these areas. Such subtle graduation doesn't play well with the H264 compression either.
With Log gamma if your camera chip is capable of, say, 12-bit colour pipeline with a DR of, say 12 stops, and your recording system is 8-bit colour H264 with a recording signal DR of 5 stops, then you are trying to not only quantise 4096 graduations of colour down into 256, but you are also trying to compress via a log curve 12 stops of DR into a picture that can be displayed within 5-stops of brightness. Hence the reason why log gamma footage looks flat.
When you grade that log footage, you are effectively stretching much of that tonal range back out again so that the picture looks normal on most displays again. The banding may not be as noticeable on the ungraded Log gamma footage, but will become apparent when it is graded.
To effectively use log gamma you really need 10-bit recording ability so that you have 1024 graduations to play with compared to 256. Cameras like the A7S are 8-bit, but they are also very low noise, which gives them a distinct advantage, although even that camera is still at risk of tonal compression issues.
Some of this can be countered by properly exposing for log gamma, and taking account of the tonal compression in the highlights. This means using an exposure that "looks" wrong on the monitor and histogram, and will appear dark. Not many people have the confidence to do that or understand how the camera is remapping the different brightness areas to the recorded file. Although it still remains that the compression system on the Inspire and the S/N ratio makes using Log gamma troublesome, and it is much better to get the location recording as close as possible to the desired final result. |
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