A7s S-Log2 grading challenge: would it be possible?

[apefos]

In the video below, there is an interesting use of S-Log2. It allows to show the background without clipping, but after grading, it introduces clipping in the background, not too much, but it clips. I was wondering if thee is a way to recover the contrast and gamma of the image, mainly in the shadows, without clip the highlights in background... Maybe a custom curve or a custom 3D LUT... See:

 

[AaronChicago]

Try using a qualifier, or a mask to keep the highlights down on the window.

[Andrew Reid]

First obviously you'd need the original S-LOG files not the graded Vimeo clip then try the EOSHD "dynamic" LUT and see how it handles the highlights

 

http://www.eoshd.com/content/13161/grading-sony-a7s-s-log-2-eoshd-cinematic-looks-download

[apefos]

Thanks @Aaron @Andrew I will take a look into these solutions!

[andrgl]

Masks are tricky (but produce the best results). I second Aaron's suggestion of using qualifiers.

 

edit: the qualifiers for the shadows+highlights is very subtle, I suggest looking at the image in tabs

original contrast - '>

shadows+highlights preserved - '>

 

[sunyata]

You're probably better off just tweaking this manually, as Aaron mentioned you can use a roto, or a comp using something like average, but here are some useful links:

 

Here's wolfcrow's A7s S-Log2 LUT. <= good preservation of shadow details.

 

Andrew's LUT's worked well for gamma conversion, but both of these appear to be also doing color transforms, so if you want to do colors separately, you can make the LUT for just the log to rec709 part on the Arri website, I found these settings to work, [set knee to 2, shoulder to 3, for better shadow details] or you can make your own. You will still need to add a gamma function after this, and you can fine tune levels.

 

Then a couple different A7s color transforms help to bring back color.

 

Not over-saturated:

 

Sony's F35 to HDW-F900 gamut conversion.

 

   1.30624    -0.233075    -0.073165

  -0.126851   1.17838      -0.051526

   0.00012    -0.085649     1.085529

 

More saturated:

 

S-Gamut to sRGB gamut conversion (If you're shooting S-Gamut) taken from the Nuke 8 colorspace node.

 

    1.87785       -0.794119     -0.0837315

   -0.17681        1.35098       -0.17417

   -0.0262054   -0.148442      1.17465

 

Link to these two 3D LUT's saved as cube files .

[richg101]

had a play, and even the low bitrate downlaod files gave enough headroom to get smoother highlights when grading the untouched s-log.  simple curves gave more highlight information than the non s-log.  Technicolour couldnt make this stuff look nice.

 

 ultimately, nothing cinematic would ever be shot like this.  there would be fill light.  this type of material (a fat woman talking about something political (or about vegan food) has no need for wide dynamic range anyway.  

 

I think the main point this topic makes is that shooting wide dr is pointless unless the subject material demands or benefits from it.  Shoot Neutral creative style and leave the s-log till it's needed...