A Note to self while working on the fades for the BBC. … It was proving impossible to find the correct LUT for the camera the production team used. In the end we did it all by eye. …. Of course once the production had finished the correct LUT files were found …

A LUT is needed when working on digital film images. I.e.The RAW frames from the sony F35 camera are normally encoded in sonys s-log color space. A LUT converts the image into a new color space. If you view RAW digital film images without a LUT they can appear very flat and washed out

You can convert when you capture data from the camera. BUT if you are working in 10bit space then you need to keep the data as s-log. If you convert the images to 10bit linear you lose data, that may show up as artifacts when the images are graded. This means that that a technical grade to linear colour space when you import the footage will loose data if you save your files as 10bit linear dpx files.

DDC/CI is a proticol that allows the graphics card to talk to the monitor. This allow you to setup Hardware LUTs that are faster than software LUTs

In theory this means that my geForce card will talk to my NEC multiSync LCD2490WUXi2 which supports 12-bit internal programmable lookup tables (LUTs) for calibration.

A viewer LUT is used to display the image in linear color space. Bare in mind that all Monitors apply there own gamma to the image. This could be rec709 sRGB, Adobe RGB color space, or ….

Wikipedia … ‘sRGB uses the ITU-R BT.709 primaries, the same as are used in studio monitors and HDTV,[1] and a transfer function (gamma curve) typical of CRTs. This specification allowed sRGB to be directly displayed on typical CRT monitors of the time, a factor which greatly aided its acceptance.’

So to get from the the RAW camera data to something what we see in reality then we need to ..
Convert s-log to Linear then Linear to the Monitor colour space

So we need a camera LUT AND a monitor LUT to view the image correctly … (and a properly calibrated monitor…)

so…. from the Sony f35 white paper

The formula representing the S-Log curve is as follows.

y = (0.432699 * Log10(t + 0.037584) + 0.616596) + 0.03

where t ranges from 0 to 10.0, representing 0 to 1000% input light level to a camera.
Multiply y by 100 to get the percentage.

The reverse curve is expressed as follow.

Y = Power(10.0, ((t – 0.616596 – 0.03) / 0.432699)) – 0.037584

where t has a range of 0 to 1.09, representing the camera output code of 0 to 109%.
Multiply Y by 100 to get the percentage.

The formula repesenting the Rec709 curve is

Lin_to_Rec709
Y = if x <= 0.018 then ( x * 4.5 ) else ( 1.099 * (x^0.45) ) – 0.099

Rec709_to_Lin
Y = if x <= 0.081 then ( x / 4.5 ) else ( (x + 0.099) / 1.099 ) ^ (1 / 0.45)

…. hmm so now i just need to plug the maths together and make it all work.