So first off, important context - I'm using these awesome film sims exactly as I do on Fuji, for no-edit JPEG shooting. This is mostly irrelevant for video shooting that's still going to be graded afterward. With that in mind...
I have a question on the logic behind the knee settings. I've noticed in the ~10 profiles I've tried out, all but one(forgot which one, but it had auto knee) of them have knee settings that result in them not coming even close to hitting full white value. In fact, there are sims that use profiles that already top out at 100 IRE, but still have aggressive knees applied, which ends up cutting max luminance off way, way under the actual 255 white clip point.
So I'm just curious what the process has been for creating the knee settings. Knee is intended for profiles that max over 100 IRE as a way to have control over how that data is brought under 100 IRE. I'm guessing it's about matching the dynamic range and highlight roll off of the film stock, but at least for no-edit photo shooting, this isn't a good way to go about it because it leaves you with images that will never hit max brightness no matter how brightly they're exposed.
What I've done for my own photo shooting is to set zebras at 100%, then go through the profiles and adjust the knee slope until zebras appear (in the case of profiles that max at 100 IRE like Cine2, is requires a linear slope/knee off, i.e. +5). This yields better dynamic range and images that actually hit full brightness, while still maintaining the most knee possible from the intended knee point to help highlight roll-off.
First of all, thank you for your question, is a really good one.
A simple answer to it is, soft Highlight Roll-off and Preservation of details.
After years of color editing I came to the conclusion that in my editing workflow I always end up soft clipping the highlights in post.
And actually, most of the times I will keep the highlights under 896 or even under the 768 mark (if you are using scopes)
Here are some quick overexposed shots with the Cine1 Gamma set at Knee Auto and Knee 75%+1
Let's compare the differences.
Gamma Cine1
Knee Auto 100% Mid (Default for Cine1)
Gamma Cine1
Knee Manual 75% +1 (exaggerated Knee)
As you can see, Highlight retention is better on the Second Image
Knee Auto 100% Mid
Knee 75% +1
Notice how the Orange bricks are shifting towards green and loosing details when shot at 100% Mid?
On the manual settings the highlights are softer, less green shifting in the orange bricks and more details are preserved out of the box.
The color of the brick is very similar to the color of Human Skin, just imagine doing portraits and the brigther parts of the face shifting towards green just like in the images presented above. Not very pleasant.
This was shot on a Sony RX100 VI which is an older sony camera, newer models should have fixed the green hues shifting, but still by using a custom knee value like 75% +4, you will get softer transitions in the highlights.
Also check the copes to see how Knee on Manual settings helps distribute details evenly in the highlights, rather than crushing them completely
Knee Auto 100% Mid
Knee manual 75% +1
The differences is more pronounced in the Blues, because the blue skies are clipping the most.
To be noted I would not use 75% +1 because it's too aggressive on color picture profiles, it's just for exampling the results.
Pushing the Knee settings has to be very subtle, as you can see, some of the skies seem a little bit crushed because of the hard settings. Maybe a +3 Slope would have helped in that matter.
Each Gamma has a different max output and can be push more or less in order to get natural results. For example, Still Gamma can be pushed to 75% +4 while Movie Gamma can be pushed down to 75%+3 or even +2
Some gammas can take this kind of setting, and some look better at higher values.
I've chosen the settings very carefully after testing them myself in real life situations.
If you'd like to reach higher white points, you can definitely change the knee settings, it's not a deal breaker.
remember, if you set the Knee level to +5, no matter what is the procentage of the slope, 75-105%, the Knee will be disabled, meaning you will have full data with pure white highlights.
If you plan on color correction, disabling the Knee this might be the best choice, to offer a full range of data to the editing process. Gammas like Cine1 can actually record superwhites, meaning over 100 IRE, which can be easily recovered in post.
Another excellent example of how knee can save information:
75% +1
Knee Auto 100% Mid
And one example when Knee is set too strong>>
Knee Auto 100% Mid
Knee Manual 75% 0
Last example shows how a strong knee setting can actually destroy the image. You can see the skies are becoming gray, and the roll off is starting to be affected by a strong knee effect.
For color profiles I found 75% +2 to be ok, but most commonly 75% +4 to be the minimum setting I would personally go. For BnW you can crush the whites even more.
One good example is the Chroma Fade Sony Film Simulation which has 75% -2 and it looks really nice being compressed, but only because it's a Black n White Film Simulation.
Samples of Chroma Fade Sony Film Simulation
Hope this helps. :]
Improvements are always welcome, so if you ever feel that some knee settings on particular film simulations should be adjusted, your feedback would be very much appreciated.
Just make a new post on the forum showcasing your results,
Thanks and have a lovely day! :D
Really excellent explanation and examples, especially looking at the individual channel clipping, which I didn't think to do since I'm mostly working in Lightroom. Much apprecaited!