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Composite hookup?


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#1 Andy Yeomans

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Posted 19 April 2007 - 06:35 PM

When hooking up my FX1 to my high-def TV through the composite hookups (RGB), am I getting a true high-def image on the screen or in there a loss in resolution through the cables? The image seems to sometimes fluctuate, but it could just be me.

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#2 David Bradley

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Posted 19 April 2007 - 08:55 PM

the fluctuations you describe may relate to the crappy mpeg 2 compression featured on the FX1. The image is HD in that it consists of 1080 lines of vertical resolution but it uses intraframe compression. HDV encodes only the differences between pixels (in fact, only the differences you can see). This compression can cut the data rate by 80 percent. That's a 5:1 compression ratio, which reduces an initial bitrate of roughly 124 Mbps to a recorded bitrate of 25 Mbps (DV rate) after compression.
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#3 Andy Yeomans

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Posted 19 April 2007 - 11:13 PM

Damn, I didn't realize the compression was that extreme! So when filming with a Viper or Sony 900 in uncompressed mode, would I be getting the rate of 124Mbps?

Are there cameras that have a higher rate than that?

What would be the compression ratio for VideoStream (RGB) mode on the Viper?

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#4 Matt Sandstrom

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Posted 20 April 2007 - 05:31 AM

the component (!) output is supposedly before the mpeg compressor, so you should get the full hd. analog cables don't have bitrates, but depending on the cables used you can get interference of all sorts. what exactly is wrong with the image on the monitor?

/matt
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#5 Andy Yeomans

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Posted 20 April 2007 - 10:28 PM

I was doing some sky tests with F/Stop, ND Filters and white balance, and while comparing the results it would seem that I would gather random noise in the image with similar stops and filters but different white balance.

Am I getting noise based on white balance? I was testing while balancing through different gels.

Edited by Andy Yeomans, 20 April 2007 - 10:29 PM.

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#6 Matt Sandstrom

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Posted 21 April 2007 - 07:13 AM

do you have agc turned off? even if it was the hdv codec, a locked down shot of a sky wouldn't show any artifacts. and a cable problem would cause the same amount of noise throughout.

/matt
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#7 Andy Yeomans

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Posted 22 April 2007 - 03:57 PM

I couldn't find a way to turn the AGC off, only a way to minimize it. I asked in a previous post but got no responses. Here is what I did to limit it:

After going into the picture profile of which I already saved, I adjusted the setting for the AE Shift to the max of +7. From what I can tell, the exposure does not shift when going from light to dark areas. Also I set the AGC (Auto Gain Control) Limit to 0dB...even though I have the camera in manual mode I don't want to take any chances in adding gain automatically.

If you know of a better way to fix this, please let me know, that would be much appreciated.

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#8 Michael Collier

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Posted 23 April 2007 - 04:40 AM

noise induced by white ballance is common, I mean after all its just an ajustment to the data coming out of the chip. Any change in that regard can highlight noise. Noise comes from an EMI base in the chip that randomly charges pixels, this noise is a constant. However manipulations will show this base noise level. the more you amplify a chanel the more noise.

when whitebalancing, certain chanels are boosted depending on the light you balance under, so it stands to reason that the more extreme balance you request, the more noise (IE a balance under 1/2ctb filter would have less noise than 1 ctb.)

It sometimes cannot be avoided to use whitebalance (when under floros for example) but you can get your camera as close as possible with glass filters to reduce the work the electronic white balance does. ENG cameras have their filter wheels, but prosumer cameras don't have any wheel. I have not yet found a reliable answer as to weather these cameras are nativly balanced at 3200k or midway bewteen 3200 and 5600, but almost every CCD or CMOS chip comes nativley in tungsten balance (a distinction resulting from the dyes used in the bayer mask)

Bottom line if noise from white balance is a concern, do everything you can to filter it to the correct light and use your presets (preset tungsten is usually best with 85 filter under daylight) glass filters induce no noise, though it will cut the sensitivity of the chips.

also note that these white balance noise problems are worse in prosumer cameras, since their DSP is in a lower byte-width (usually 10 or 12 max, pro cameras run in 14 or 16 bit)

hope that helps
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#9 Andy Yeomans

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Posted 24 April 2007 - 10:01 PM

This is really good information, thank you.

Now for another question:

How do I calibrate my CRT monitor to view footage from the camera AS IS?

I remember adjusting an lcd and following the steps of adjusting the brightness and contrast all the way up. Because there is a big difference when watching footage from an lcd and the same stuff on a CRT, the image always seems to be brighter on the lcd and closer to what is real.

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#10 Matt Sandstrom

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Posted 25 April 2007 - 06:40 AM

you calibrate it like an sd monitor, by outputting bars then adjusting the brightness until the black is just barely crushed, then using the blue only function and tweaking the color until you see four bars of the same intensity.

crt hd monitors are insanely expensive though. if you have one chances are you're renting it and then you can have the rental company calibrate it for you. the crt hd tv's aren't really hd since their masks only have like 500 lines.

/matt
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#11 David Bradley

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Posted 25 April 2007 - 04:55 PM

Andy

Use SMPTE bars to properly configure your monitor.

-Use the camera to display SMPTE bars on the monitor
-turn the colour off or all the way down.
-note the 3 thin bars at the bottom right of the monitor known as PLUGE bars; adjust brightness or luminance until the left most bar is as black as the middle bar. You should still be able to distinguish the middle bar from the right.
-Turn the colour back to the middle.
-Press the blue only button on the monitor (if it has one) or use a blue filter such as wratten 80A layered until you can see no other colour but blue.
-Adjust the colour until the bar in the top left is exactly the same tonality as the bar on the very right of the spectrum. (there may be a reference below the bars to assist.)

I wouldn't rely on the rental house to calibrate the monitor as you need to re-adjust it every time there is a significant change in temperature or it has come under an impact of any kind. During video shoots when the the DP and the Director rely upon the monitor it is proper to have an assistant recalibrate the monitor every half hour / hour. Make sure it is shielded from light when calibrating.
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