OT Knee settings for SONY PMW 350

Jay Gladwell wrote on 4/25/2010, 4:16 PM

That depends on several factors. For example, what gamma setting are you using?

farss wrote on 4/25/2010, 5:18 PM

Please keep this discussion going.
This is an area that still causes me some grief.

EX1, STD3 mostly.

Bob.

Jay Gladwell wrote on 4/25/2010, 5:59 PM

What kind of grief, Bob?

farss wrote on 4/25/2010, 7:01 PM

I switched Auto Knee Off and didn't change the default knee from whatever it is, 60% I think. End result was some very funky blown out highlight, think solarized, not good.

I understand why that happened and that I was a bloody fool for playing with a camera setting without testing and really understanding what I was doing before the shoot.

I shoot of lot of black on black and leave Auto Knee On and really watch my zebras (set Zebra 2 to 60%) and generally get good results all things considered however if I get a mixture of black skin and caucasian skin in the one shot get rather plastic looking skin tones on the caucasian skin. I'm fairly certain this is from the auto knee.

I really don't have the space on many shoots for a good HD SDI monitor, judging these things in the tiny EX1 viewfinder is not easy and I really don't get enough time to setup a camera before I have to roll so I need to either follow good advice (which can be well intentioned but completely bad for some shooting scenearios) or else test, test, test however that's not as easy as it sounds.

Bob.

megabit wrote on 4/26/2010, 12:47 AM

No way could your Caucasian skin tone be affected by standard knee setting, Bob - it's at 90.

farss wrote on 4/26/2010, 1:05 AM

No matey, in that case it was some silver wings on fairies in the full Australian sun.

Please don't laugh anyone, they were for real and rather cute and it was in the grounds of Government House.

So what I guess goes wrong with knee at 90% is by the time the 100% zebras kick in things could be getting ugly and sensor overload not far off. Lesson learned the hard way.

My problem from time to time is with Auto Knee On and mixed black and caucasian skin tone. Well maybe not, when I've read others complain about this 'plastic' looking skin the comment is to do with Auto Knee being On. I'm trying to think how to run some tests but none of the standard test charts seem to me to be of much help.

Bob.

megabit wrote on 4/26/2010, 1:09 AM

Bob,

One thing I'm not sure of is whether "Auto" applies to the slope, or the point itself.

If the latter, indeed funky stuff may happen with knee auto.

I never investigated it much (apart from testing some extremities), as I tend to use cine gammas, anyway.

Piotr

Jay Gladwell wrote on 4/26/2010, 5:18 AM

Bob, since you're using one of the Standard gammas, try adjusting your knee "Point" setting to somewhere in the 85 ballpark. That should help with the highlights without creating the funky solarized problem.

cspvideo wrote on 4/27/2010, 4:41 PM

All this dicussion is helpful!

And yes, to the first, question, knee is dependent upon other settings. I'm interested in hearing about what others are using and the advantages and disadvantages of their particular choices.

Thanks for all of the input to date.

Jay Gladwell wrote on 4/27/2010, 5:06 PM

"I'm interested in hearing about what others are using and the advantages and disadvantages of their particular choices."

In truth, what others do or don't do have no bearing on you and your preferences. What looks good to you may not look good to me, and vice-versa.

It sounds to me that you need to do some of your own research into the paint settings of your camera. You also need to determine what "look" most appeals to you.

I strongly encourage you to go to DVinfo and do some serious reading there in the EX forum. You need to learn this for yourself, rather than have someone spoon-feed it to you. It will make you a better videographer!

farss wrote on 4/27/2010, 7:44 PM

Found from DVInfo that is reasonably helpfull in explaining what things do:

A search at DVInfo should also find a series of posts from our very own Serena who went to considerable trouble to plot all the EX gamma curves. This is far better information that what Sony managed to supply with the camera.

One thing to keep in mind, I'll admit it took me sometime to get my head around this, is that the curves plot actual light to recorded levels. When Sony refer to 100% to 450% mapping to 100% to 109% the input value at 100% is where the 100% zebra diplay. Brighter values than what the camera 'sees' as 100% will map to the 100% to 109% values. These values are outside broadcast levels and you may (or may not) need to wrangle that in post. Putting anything other than specular highlights into that region can cause some funky outcomes as there's not too many bits to accurately describe the image. Take care with clouds for example.

What I see as the biggest problem futzing around with knee and slope is without a waveform monitor you can land youself in a lot of trouble. With extreme settings what might look great can bring you badly undone under slightly different lighting setups. Jay is spot on, too many times people have posted some magic soup that produced great images and then others try them and get horrid results.

Bob.

megabit wrote on 4/27/2010, 11:34 PM

I totally agree that changing defaults for knee only makes sense on a specific scene basis.

cspvideo wrote on 4/29/2010, 7:50 PM

Snarky Jay. Snarky.
I am fully aware it's a user preference setting. I was simply asking people what they were doing and why they liked it or disliked it. I was starting a discussion about rationale. Thanks for the counsel on how to become a better videographer.