Plus and minus values in PP settings EX1r

[David Morgan]

It's unclear to me what is meant by the plus and minus value settings in the following:

PP knee slope: After turning off Auto Knee, which direction do you go if you want compression, Plus or minus?

[Alister Chapman]

A plus value for the knee slope increases the amount of knee compression, minus value is less knee compression. Be careful with too high a positive setting as you might never reach peak white (depends on knee point). It's best set up with a waveform monitor.

I tend to use the standard slope and then just adjust the knee point to suit. My typical setting for the knee point is 85.

[David Morgan]

yes, I set my knee point to 85. I'm using a +5 compression. It's a subtle effect. Question is, what does plus mean? Is it related to IRE units? i.e. +5=5 IRE units or?

[Alister Chapman]

I don't think the slope number has any meaning, just plus or minus, more or less.

About the only PP setting that has a real value is the knee point (IRE).

[Chris Medico]

And if you choose a low knee point try to keep skin tone highlights out of that range if possible.

Highlight compression on skintones really stands out.

[Walter Brokx]

Slope value does have it's effect.
It's comparable with compressing or expanding audio (this is a technique that changes the dynamics of the sound, not to be confused with saving compressed data).

With audio +2 would mean that sound above the knee-value gets compressed at a 1:2 ratio. 2 dB above knee results in 1 dB above knee. 4 -> 2 (etc).
With +4 this means that 4 dB above knee will be 1 dB above knee.

I guess the EX-camera's use the % values.
Setting the knee to 85 means the above 85% the slope changes.
+2 probably means the slope is dicreased at a 1:2 rate.

Heavy slope values will lead to loss of detail and large monochrome surfaces.

I made a backlight-profile to be able shoot shadowy architecture and still have some details in the sky.

[Russell Heaton]

Hello Walter

Would you consider sharing the backlight profile? I could use a profile like that and whilst I could probably come up with something over time, it doesn't make sense to reinvent the wheel. I'm sure that others would be interested in your profile as well.

Cheers

Russ

[Alister Chapman]

Originally Posted by Walter Brokx

I guess the EX-camera's use the % values.
Setting the knee to 85 means the above 85% the slope changes.
+2 probably means the slope is dicreased at a 1:2 rate.

Heavy slope values will lead to loss of detail and large monochrome surfaces.

Knee Point is the actual IRE value of the knee onset point. It's not quite the same as the % value as the EX cameras can record up to 109%. The Knee is a soft knee so there is a small amount of compression just below the knee point with full compression reached at the knee point.

The slope level setting modifies the default knee slope which is around 1:2.5 at zero (I need to check this on a WFM), there appears to be no direct relation ship to the slope compression and the number used, it is purely a modifier. I don't think +99 would mean 1:99 and I'm not sure what -99 would mean?

To avoid loss of detail and large monochrome surfaces, if you adjust the slope you should really be adjusting the Knee Sat Level for colour and Knee Aperture for detail, although this is hard to get right due to the compressed nature of the image above the knee point.

[Walter Brokx]

Thanks for the IRE info!
I already thought it has a soft knee.
Maybe you are right that 2 doesn't mean 1:2, but it's still clear that higher values have more effect.

Negative values would mean that lightness will be amplified above the knee.
I never tried it, but it will probably produce weird images with clear posterizeng when you use high values.
-99 will probably blow out the signal above the knee, lol.


About the backlight profile:
take ur favourite profile, copy it and change knee and slope.
I believe I set knee to around 87
And slope to 20.
But when the image needs it, I change it.
It's just a way to prevent blownout skies. Be carefull when people show up in the brighter areas: they will look terrible, lol.

[Alister Chapman]

Negative values mean a less steep slope than sony standard. So -20 is less compression than zero, but the actual value is unclear.

The EX1 and EX3 normally record unto 109 IRE. This is Superwhite and is the brightest white that a digital camcorder complying to normal 8 bit or 10 bit video specs can record.
If your using a slope of +20 you don't want to bring the knee point lower than 88 as you will be over compressing and the highlights and won't ever reach 109 IRE. Bring it down to 87 and peak white only gets to 108, at 85 you get 106 and at 80 just 101 ( although this is one way to create a broadcast safe profile). So with the knee at +87 with the slope at +20 you are not making use of the full data and brightness range available to you. Better to set the knee to +89 or higher when the slope is +20.

You really need to set up knee values with a Waveform Monitor to make sure you don't over compress. A lot depends on whether your working to the almost now standard Superwhite at 109 IRE or the broadcast safe 100 IRE. 100IRE on a computer monitor looks like a slightly grey white.