Bright top and bold contrast

[Nicolas Hanson]

I met a senior colorist from Nightshift in Paris that mainly works with fashion commercials and fashion in motion films. See told me that one of her techniques to achieve a bold contrast and at the same time a very bright top was to 'bend the top' with the lift control inside a node with a 3D Lut applied. I have found that it's a huge difference in the way the highlights respond from working on this node compared to the next one in the tree. It feels like I can push the brightness forever without clipping them and still retain a bold contrast. Can someone explain what is going on? 

[Andy Minuth]

I am not 100% sure, if I understand how this technique works.

But when you grade before a typical Log-to-Video-LUT is applied, You are benefitting from the soft highlight rolloff. Which means, your grade is sent through a s-curve, that becomes very flat in the highlights. So when you make the image brighter, the result will not clip easily, but only when you push it very hard. Basically you can make the image brighter and darker without clipping in the blacks or whites or loosing the general contrast. The contrast in the highlights will be reduced of course, because of the flatter curve in the LUT.

I hope this makes a bit sense  

[Nicolas Hanson]

Thank you for explaining this to me, but how can the great be sent through a s-curve if the correction is applied before the LUT? Isn't that exactly the same as doing the corrections without a LUT at all?

[Andy Minuth]

First the corrections are applied, then the LUT. You are looking through the LUT while grading.

Just put a grading operator before and after a LUT and observe the behavior on the waveform as you change the brightness in each one of them. You will notice a big difference. If you use a gradient from black to white (left to right) as source image, you can see the s-curve on the waveform.

[Nicolas Hanson]

Now I understand, thank you very much for your help.