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#1 Ken Minehan

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Posted 08 September 2005 - 02:35 AM

Hey guys, i was wondering, how the DCC function affects the dynamic range. What is the finction of DCC? Is it recommended if so for what circumstance?
Thanks guys. I am having trouble looking for info on this.
Hope you can help.
Cheers
Ken
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#2 Tim J Durham

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Posted 08 September 2005 - 07:31 AM

Hey guys, i was wondering, how the DCC function affects the dynamic range.  What is the finction of DCC?  Is it recommended if so for what circumstance?
Thanks guys.  I am having trouble looking for info on this.
Hope you can help.
Cheers
Ken

<{POST_SNAPBACK}>

DCC (dynamic contrast control) turns on and off a pre-set white clip. When you shoot for broadcast, the FCC requires that the luma and chroma signals add up to no more than 130 IRE (if I recall correctly), so if you have a blown out portion of your scene, you can engage the DCC and it will bring the white clip point down, saving you some chroma info.

If you are not shooting for broadcast, all it's doing is reducing your dynamic range and you may or may not want that. Sometimes it makes the highlights look posterized if not set-up carefully.
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#3 Ken Minehan

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Posted 09 September 2005 - 01:41 AM

DCC (dynamic contrast control) turns on and off a pre-set white clip. When you shoot for broadcast, the FCC requires that the luma and chroma signals add up to no more than 130 IRE (if I recall correctly), so if you have a blown out portion of your scene, you can engage the DCC and it will bring the white clip point down, saving you some chroma info.

If you are not shooting for broadcast, all it's doing is reducing your dynamic range and you may or may not want that. Sometimes it makes the highlights look posterized if not set-up carefully.

<{POST_SNAPBACK}>


Thanks Tim. That is very helpful.. I shot something with the DCC on. I couldn't work out why the Shot looked so hazy. I think it was due to the DCC.
Cheers
Ken
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#4 Tim J Durham

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Posted 09 September 2005 - 08:50 AM

Thanks Tim.  That is very helpful..  I shot something with the DCC on.  I couldn't work out why the Shot looked so hazy.  I think it was due to the DCC. 
Cheers
Ken

<{POST_SNAPBACK}>

Hi Ken,
It's unlikely that the DCC was responsible for "hazy" looking video. What might happen if you have the DCC set improperly is the highlights would cluster and look like one blob as opposed to
having the subtle differential shades. I'd have to see your video to determine what made it "hazy" looking, but it would not be the DCC.
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#5 Tim J Durham

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Posted 09 September 2005 - 08:52 AM

Hi Ken,
It's unlikely that the DCC was responsible for "hazy" looking video. What might happen if you have the DCC set improperly is the highlights would cluster and look like one blob as opposed to
having the subtle differential shades. I'd have to see your video to determine what made it "hazy" looking, but it would not be the DCC.

<{POST_SNAPBACK}>

Actually, even if you DO have the DCC set properly, you'll get some clustering at the clip level. That's why, unless I'm shooting for broadcast, I don't use it.
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#6 Alvin Pingol

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Posted 13 September 2005 - 03:49 PM

I've also found that at times, DCC will give false colors to the highlights, which can look really odd. I now leave it off for the majority of my shoots.

EDIT: I was referring to my SD camera; didn't notice the HD thread but it's still video nonetheless...
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#7 Mike Brennan

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Posted 25 September 2005 - 06:41 AM

DDC has nothing much to do with white clip.
It is a floating knee point, compressing highlights.
It outperforms most users trying to input manual knee settings on location.
Leave it on.
Be carefull when using it with knee saturation.
Be carefull that it doesn't clamp quickly and noticibly.


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#8 Tim J Durham

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Posted 25 September 2005 - 09:18 AM

DDC has nothing much to do with white clip.
It is a floating knee point, compressing highlights.
It outperforms most users trying to input manual knee settings on location.
Leave it on.
Be carefull when using it with knee saturation.
Be carefull that it doesn't clamp quickly and noticibly.
Mike Brennan

<{POST_SNAPBACK}>

Yes, my description of what the DCC is actually doing was lacking. You can't say it "has nothing much to do with the white clip point" though either. Here is a more thorough description (which cannot be had from Sony or Panasonic):

Here is a short description of what is going on in the Knee circuitry with the F900 /3 camcorder. Basically, there is a circuit for condensing or compressing the more than 100% video levels output from the CCD's. It tries to push down the signal derived from any overblown highlights, to a level that can be successfully recorded to tape. In other words, it tries to push the signal down so it is below the white clip point, which is usually around 100% (or perhaps a little higher). The white clip point is a high frequency filter that completely cuts off the signal at a specified level (usually between 100% and 108%).

A completely automatic knee circuit/s is controlled by the exterior DCC switch on the side of the camcorder (DCC = Dynamic Contrast Control). When DCC is switched ON, an automatic knee circuit is set in operation . It completely overrides any setting made for point, slope and clip in this menu, and acts as a fully automatic knee circuit (or "auto knee"). The higher the signal in, the more this automatic circuit tries to compress the signal, and compensate for overexposure of the highlights. Originally designed for ENG type applications, it tries to compress overblown highlights to below 100% in an effort to make it suitable for the normal parameters for broadcasting television. However, when the DCC switch is turned OFF, this activates the Manual Knee according to the parameters set in this particular menu (Paint #6). This allows for a a fixed level of compression within a fixed time frame.

TIP: Auto Knee, or DCC (Dynamic Contrast Control), can offer a greater degree of compression for extreme highlights. Many people cringe at the thought, but it is sometimes better to let DCC take control of your highlights ..... but I must emphasize, only in certain lighting scenarios. It is not always the case, but sometimes DCC can out perform a carefully established manual knee settings, and simply make the extreme highlights in your image look better and more pleasing to the eye. So DCC is not necessarily just an ENG thing, as it can also be a useful tool for dramatic shooting as well. DCC works best where you have one predominent highlight element that is widely separated in level from the other highlights in the image, for example an open window looking at a bright sunlit exterior, or a naked light bulb. However, if all your highlight elements are closer together, then both manual knee and auto knee tends to make all your highlights go muddy looking, even those below 100%. If in doubt, I suggest you switch between auto knee and manual knee before you roll, and see which one looks better in the highlights. You might be surprised ..... well sometimes.

Having said that, I mostly prefer to turn all Knee circuits OFF completely, so no manual or auto knee compensation at all. Aesthetically speaking, I really dislike the look of knee compression most of the time, and would rather let the highlights burn out "naturally" (in a similar way as is often done with exposing film). Knee compression usually makes your extreme highlights go muddy looking and lacking a certain inner brilliance. So exactly the opposite of how burning out highlights should look logically speaking, or how you'd expect them to look intuitively. Just to give you an idea, I might shoot without knee compression say, 70% or 80% of the time, with manual knee control about 15% or 20% of the time, and with auto knee or DCC activated less than 5% of the time. Of course, these ratios might change significantly with the project, and especially with the type of lighting encountered.

Note: If the Knee is set to OFF in the camera menus (in either Paint #1 or Paint #6), then the manual knee circuits are disable, and there will be no knee compensation made to the signal. However, the operation of this menu is tied to the position of the DCC switch on the side of the camcorder. As soon as the DCC switch is activated (or switched ON), it overrides the OFF setting in the camera menus and turns the the knee circuits ON. Further, it overrides any and all setting in the manual knee menu, and activates the automatic knee circuitry. The operator has no control over how this circuit tries to compress the video signal that is 100% and above. But when the DCC is subsequently turned OFF, the manual knee is left ON, and the manual knee circuits will be in operation (even though they were turned OFF originally).

http://jkor.com/peter/F900paint.html

So atleast I knew "why" I did/didn't want to use it. And if you watch on a waveform while you switch it on/off, it is (can be) lowering the white clip point but is also doing more than that. So
I stand (somewhat) corrected.
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#9 Dimitrios Koukas

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Posted 25 September 2005 - 09:27 AM

The DCC can be really helpfull when u have to deal with really contrasty scenes like windows in the background, that you actually want to see what is going on out there, and also have not so much light inside or no ND to the windows to compensate.
It reacts more like a film, adding more details at the highlights.
In case you have an rcu or ccu, it is better to control the latitude of your image by the knee point knob.Like the other dp's here said, it compresses the signal down, same function that the knee does if u see it on a waveform monitor.
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#10 Mike Brennan

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Posted 02 October 2005 - 06:42 AM

Yes, my description of what the DCC is actually doing was lacking. You can't say it "has nothing much to do with the white clip point" though either. Here is a more thorough description (which cannot be had from Sony or Panasonic):

http://jkor.com/peter/F900paint.html

So atleast I knew "why" I did/didn't want to use it. And if you watch on a waveform while you switch it on/off, it is (can be) lowering the white clip point but is also doing more than that. So
I stand (somewhat) corrected.



We may be stuck on two differnet interpretations of the word "clip" so we are both right:)

They way I see it is
White clip is the ire output limit (to tape) that is defined manually.

Jeff Cree says tape will record 109 ire but reccommends 106ire as tops.
Transmission systems cope with 100ire
Sony says that ccd saturation occcurs at about 130ire, perhaps 2 stops over 100ire.

Without knee everything above whatever the white clip is set to 130 will be lost to tape.
With manual knee we can adjust the slope and knee point that compression kicks in but limit output to white clip (say) 106%
With DCC slope and knee point are dynamic but happens to white clip?

Sure the dcc may pull levels down below 106% so on a scope it looks like clipping but perhaps you are seeing 130ire saturation bought below 106%?

It doesn't mean levels above the peak are clipped, just that they are are pulled down below the output level.
The clip level is unchanged as the dcc seems to always limbo under it....


As an humourous aside, the source of your quote is from a website that contains direct copies of Sony's Jeff Cree's Santas Fe powerpoints.
For 2 years the website owner didn't even credit his source, preffering to take credit for the info screenshots and all, himself, despite protestations from Sony.
So to say the expaination of how knee works is hard to come by from Sony is under the circumstances ironical.




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#11 Tim J Durham

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Posted 02 October 2005 - 09:26 AM

Mike,
I accept your definition of white clip, you have pretty accurately described my interpretation of what goes on when you switch on the DCC.

I would love to be able to get info from the horses mouth so-to-speak. If Sony would make it available in an easier way than to take one of their engineers out to dinner, I would ALWAYS quote Sony (engineering dept, atleast. NOT the marketing hoards). Doing a google search for Sony info rarely brings up a www.sony.com link. That's THEIR own fault as far as I'm concerned.

This doesn't excuse the guy with the website from plagiarizing proprietary info, however. So I will refrain from quoting him again.
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#12 Phil Rhodes

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Posted 02 October 2005 - 11:36 AM

...and this is why we have Viper.
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