Some footage...

FelixGER said:
That´s odd. In this document the knee slope is the exact opposite. Minus = steep and plus = gentle
Click to expand...

I believe the idea is you want to control the INTERSECTING point to the horizontal line. You're controlling how much illumination (X-Axis) you are getting WITHIN the confines of your white clip point (Y-Axis).

So find your Y-Maximum then adjust your horizontal movement along that Y-Maximum. So in the example Y-Maximum = 109%. Then that becomes your Y-Constant (Y-Maximum = Y-Constant). Now as you adjust your slope it will intersect at various points along that Y-Constant.

We are essentially constraining our equation (the slope) along that Y-Constant (White Clip Line) so that we get a White Clip Point (hence the intersection).

I think the trick is finding out how Sony has calibrated the knee such that where Knee = 0.

EDIT:
Some things that caught my eye (I'm hypothesizing here as I'm no expert):
- Sony notes that this is a proprietary implementation as Sony explicitly notes that this is only on "Sony Cameras" so other Knees use different equations.
- The main thing Sony wants you to know is that an INCREASING Knee value extends the use of the video camera's dynamic range. Sony managed to increase the dynamic range through COMPRESSION. So as Knee increases so does the dynamic range of the camera BUT only through compression so things like noise should be taken into consideration.
- Sony notes that as Dynamic Range of the camera increases, the risk of getting a washed out image also increases.
- Therefore the opposite is true, a lower Knee value decreases dynamic range but also decreases noise and colors should look more full as there is less risk of being washed out.
- The document also recommends the complementary aide of the "Knee Function" and "Knee Saturation" function. So what this tells me is that they've applied a similar Knee Function (equation) to other aspects of image quality to help aide the use of their knee for dynamic range. Kind of like a drug to aide in side effects of other drugs. Anyone see these complementary aides on the FS100?

QUESTION:
- How does Knee Point relate to Knee Slope and the White Clip Point?
 
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ectobuilder said:
I believe the idea is you want to control the INTERSECTING point to the horizontal line. You're controlling how much illumination (X-Axis) you are getting WITHIN the confines of your white clip point (Y-Axis).

So find your Y-Maximum then adjust your horizontal movement along that Y-Maximum. So in the example Y-Maximum = 109%. Then that becomes your Y-Constant (Y-Maximum = Y-Constant). Now as you adjust your slope it will intersect at various points along that Y-Constant.

We are essentially constraining our equation (the slope) along that Y-Constant (White Clip Line) so that we get a White Clip Point (hence the intersection).

I think the trick is finding out how Sony has calibrated the knee such that where Knee = 0.

EDIT:
Some things that caught my eye (I'm hypothesizing here as I'm no expert):
- Sony notes that this is a proprietary implementation as Sony explicitly notes that this is only on "Sony Cameras" so other Knees use different equations.
- The main thing Sony wants you to know is that an INCREASING Knee value extends the use of the video camera's dynamic range. Sony managed to increase the dynamic range through COMPRESSION. So as Knee increases so does the dynamic range of the camera BUT only through compression so things like noise should be taken into consideration.
- Sony notes that as Dynamic Range of the camera increases, the risk of getting a washed out image also increases.
- Therefore the opposite is true, a lower Knee value decreases dynamic range but also decreases noise and colors should look more full as there is less risk of being washed out.
- The document also recommends the complementary aide of the "Knee Function" and "Knee Saturation" function. So what this tells me is that they've applied a similar Knee Function (equation) to other aspects of image quality to help aide the use of their knee for dynamic range. Kind of like a drug to aide in side effects of other drugs. Anyone see these complementary aides on the FS100?

QUESTION:
- How does Knee Point relate to Knee Slope and the White Clip Point?
Click to expand...

Ooops!! I guess I got this one backwards. It's weird though, at positive values, my highlights were much quicker to blow out. Even to the point of having a cloudy sky at negative values and having only white at positive values.

Ya know what though, its possible that the LCD just couldn't display info that was there.

I gotta do a real test with this.
 
ectobuilder said:
QUESTION:
- How does Knee Point relate to Knee Slope and the White Clip Point?
Click to expand...

It's pretty simple as far as I can tell, knee point is the luma level at which knee gamma intersects with master gamma, and slope is the slope of the knee gamma. These adjustments are completely independent of one another whereas white clip point is dependent upon both of those. Basically knee point chooses the point at which knee starts modifying the master gamma curve and the slope adjusts the linear(?) compression or expansion of those values. If slope is set too high such that image highlights are expanded past 109%, then those details are clipped, and if slope is set lower such that clipped image data compressed to below 109%, then clipped values will be assigned to values below 109%.

It all seems a little silly to me since all I care about is maintaining a natural curve and controlling my white level, unfortunately there is no way to quite achieve this without some compromise. I'd rather just have a white level adjustment that sets 109% or 100% and compresses the entire gamma range to accommodate and highlight gamma adjustments like we have black gamma adjustments since having a point where your gamma curve flattens to accommodate a knee always looks pretty ugly. It is really beyond me why someone decided highlight portions of an image should be handled differently and should have hard angles and straight lines in the gamma curve. Hard angles and straight lines never look good in any part of a gamma curve, so why put one in the highlights, what if the user decides to overexpose more than a little of their frame?

What's interesting is that since knee cannot be turned off, gamma curves were probably built with that in mind. From what I can tell, setting knee point to 105% and slope to 0 is basically like turning the knee off and letting the gamma curve handle it the way it was designed. It does seem like the knee in this camera is a bit different from other cameras in that it seems softer at least when used with cinematone gammas, it maybe that rather than completely overriding highlight gamma and replacing it with a straight line it may just be taking the original gamma curve and compressing that a bit more, so the angles can be a bit softer. I've found that with cinematone1, setting knee point to 75% and slope to +1 gives exactly 100% white clip point without losing any highlight latitude and with a fairly subtle knee point perhaps because the adjustment is spread out over a longer part of the gamma curve. With any other setting, if you shoot a gradient and adjust the knee point, you can see the unnatural hard angle of the gamma curve at the knee point just move around and never really go away until you hit 105% @ slope 0.
 
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