S-Log2 gamma?

  • 3 Replies
S-Log2 gamma?
« on: 11 / April / 2014, 16:14:04 »
This is a real NonTechie question because I have no idea how difficult it is to implement.

Today I was very impressed with the Sony A7s Low Light (ISO 1600 to 409600) Demonstration Video
Sony A7s: Low Light Demonstration (ISO 1600 to 409600)

While I know the sensor can Not be duplicated, am wondering if the "S-Log2 gamma" can?

Am interested in any comments.

« Last Edit: 11 / April / 2014, 16:16:14 by genosmm »

Re: S-Log2 gamma?
« Reply #1 on: 11 / April / 2014, 16:18:55 »
After watching the low light video did some searching and found "Sony A7S Review -- First Impressions"
https://www.imaging-resource.com/PRODS/sony-a7s/sony-a7sA.HTM  where I saw "The Sony A7S also supports what's known as S-Log2 gamma, a tone curve borrowed from Sony's pro video recorder line that greatly expands the practical dynamic range of its videos. This special gamma function applies a strong logarithmic tone curve to the sensor's output, rolling off the highlight end of the curve to preserve highlight detail. Viewed without a corresponding tonal expansion, the resulting video will look very flat, but the dynamic range is expanded over linear encoding by 1,300%, providing enormous dynamic range that can be exploited in post-production."



Offline ahull

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Re: S-Log2 gamma?
« Reply #2 on: 11 / April / 2014, 17:44:29 »
Its not clear from the description, but I suspect the logarithmic tone curve is probably applied by hardware, to the output coming directly from the sensor. In other words, this is on chip correction of the raw analog values probably in the amplification stage before the signal hits the A/D converter.

In which case it would not be possible to emulate in software.

The correction may however be applied after the A/D stage (which I doubt), in which case it might be possible to process the raw output from the camera in a similar manner.

If it were possible to do this in software, you would require a camera capable of outputting raw video frames, and already able to produce extremely good low light performance.

Even the best canon P&S sensors really don't fall in to this category, the sensors are too small, and the noise levels are not comparable to this Sony, so the technique, if it could be applied, would still not produce results as impressive as the video, but it might provide some improvement over the standard off the shelf results. 

I suspect you may need to look for patents relating to the subject to figure out when and how this is done.

It is pretty impressive however. Thanks for sharing.
« Last Edit: 11 / April / 2014, 17:57:15 by ahull »

Re: S-Log2 gamma?
« Reply #3 on: 12 / April / 2014, 13:35:24 »

Thanks for your detailed answer.

Do you know if Canon still gets some of its P&S Camera Sensors from Sony?

Hope sometime in future Sony will be using this 7S technology in smaller P&S camera sensors and offer it to other mfrs like Canon.

another alternative is Canon develops better low light sensors.



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