Sony has been making waves with their lastest cameras and one of the most talked about is the Sony A7s. Everyone is talking about how great in low light the camera is and the fact you to shoot S-Log2 footage. All of that and the fact it is an affordable full frame camera that really seems to create stunning images is appealing to many.
What a lot of people aren't really talking about it what does working with SLog-2 really mean when you get to post? What does this mean for most people who haven't working with a Sony camera or been through post with any of Sony's SLog formats?
Please note that S-Log2/S-gamut footage has a different color gamut and color space then pretty much every display monitor you will look at. So in order to get the footage to look correct you will need to convert it to a Rec-709 color space which most display monitors use.
If you are not a colorist you might want to just apply a Rec-709 LUT in Premiere Pro so you can see the footage as it will look on a standard display monitor. What rocks about this is when you apply a LUT it is non-destructive meaning you don't change anything about the underlying footage. How cool is that?!
How S-Log2 was designed was to take a wide dynamic range (14 stops) and fit that into a camera that doesn't have a true 14 stop range. The real world result is the image you are capturing will look flat because the S-Log2 is more or less re-mapping the data to maximize the quality you can achieve in post.
When you apply a LUT and expand the S-Log2 footage back to a Rec-709 color space your footage will exceed the display capabilities of your monitor. You tend to loose data in the highlights as the overall image shifts brighter when you apply the LUT. Don't panic that your footage may appear overexposed and clipped. Your data is not lost. If you remember you are not changing the underlying clip so the data captured is there. For those that have tried to color grade your way out of clipped highlights this will be HUGE to you as this is not normally possible. Consider it voodoo magic that makes your life easier.
If you want a real world walk through of how to do all this read this amazingly in depth article from Alister Chapman. He will make all this super simple and walk you though the whole process.
Does this make you want to shoot with S-Log2 or S-Log3? Let us know. Happy shooting!
Using S-log2 from the A7S in post production
So what is a LUT? It’s a simple table of values that converts one set of signal levels to another. You may come across different types of LUT’s… 1D, 3D, Cube etc. At a basic level these all do the same thing, there are some differences but at this stage we don’t need to worry about those differences. For grading and post production correction, in the vast majority of cases you will want to use a 3D Cube LUT. This is the most common type of LUT. The LUT’s that you use must be designed for the gamma curve and colour space that the material was shot in. So, in the case of the A7s we want LUT’s that are designed for S-Log2 and S-Gamut. LUT’s designed for anything other than this will still transform the footage, but the end results will be unpredictable as the tables input values will not match the correct values for S-Log2.
One of the nice things about LUT’s is that they are non-destructive. That is to say that if you add a LUT to a clip you are not actually changing the original clip, you are simply altering the way the clip is displayed. If you don’t like the way the clip looks you can just try a different LUT.
If you followed the A7s shooting guide then you will remember that S-Log2 takes a very large shooting scene dynamic range (14 stops) and squeezes that down to fit in a standard video camera recording range. When this squeezed or compressed together range is then shown on a conventional REC-709 TV with a relatively small dynamic range (6 stops) the end result is a flat looking, low contrast image where the overall levels are shifted down a bit, so a well as being low contrast and flat the pictures may also look dark.
To make the pictures on our conventional 709 TV have a normal contrast range, in post production we need to expand the the squeezed recorded S-Log2 range to the display range of REC-709. To do this we apply an S-Log2 to Rec-709 LUT to the footage during the post production process. The LUT table will shift the S-log2 input values to the correct REC-709 output values. This can be done either with your edit software or dedicated grading software. But, we may need to do more than just add the LUT.
Read full article at XDCAM-USER.COM “Using S-log2 from the A7S in post production”
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