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Old January 18th, 2003, 08:13 AM   #1
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0 vs 7.5 IRE

I've been using 7.5 as my cam set-up IRE. It was the default setting and Michael from 24p.com had some logical reasons for preferring 7.5 with a master ped down between -6 to -8. However, seems like many are using an IRE of "0". Can anyone explain why this would be preferable to 7.5?


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Old January 18th, 2003, 09:43 AM   #2
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As a starting point I suggest you read Adam Wilt's article on setup and DV. This will give you a good background on what goes on with setup in North America (this is not a PAL issue).

So, after reading Adam's page the only time 7.5 IRE is required, is for broadcast. When I design projects for web, DVD, VHS or virtually anything else I drop IRE to 0 to expand my contrast range and depth. I can now use a range of colors from 0 to 255, rather than 16 to 255. I would be especially interested in expanding my range if I were going to film. Film can certainly handle the increased range.

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Old January 18th, 2003, 02:08 PM   #3
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And actually you can ALWAYS leave it at 0 IRE because the machines they introduce the video into the workflow with will automatically raise it to 7.5. If you record it with setup it will wash out all of your blacks when they upconvert it to 7.5 again because the decks already add setup to digital video. Digital video NEVER has setup. Only U.S. broadcast video has setup so I would let the broadcasters add it.
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Old January 19th, 2003, 06:24 PM   #4
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It depends on how the setup is added. If they just "crop" anything lower than 16 and anything higher than 235 - or whether they compress the full 0-255 range into legal settings.

Since I am not sure who uses what at what point in the chain, I make sure everything is proper with 16 RGB being setup to 7.5 IRE and the same for 100 = 235.

IF... I ever have a need to go back to film, I can then stretch back evenly 0-255.

Also - the camera never shoots down to 0 RGB regardless of setting. Chips shut down around 3 RGB.

7.5 Setup with -8 Master Pedestal creates 16RGB and 7.5 IRE on a waveform/vectorscope for pure black (lens cap on)

0 setup and -6 Master pedestal creates the same black levels as 7.5 with -8.

The difference between 0 and 7.5 only lowers 2 IRE on the scopes and not the expected 7.5.

So - after all these tests, I have a known value starting point with 7.5 setup and -8 pedestal for black.

Using that as a guide, I will use MAster Pedestal settings of less than -8 for more detail in shadow as needed depending on the scene.

That is what I go with this setting. But everyone needs to find their own "starting" point with the camera and then create the images they want from there. There is no real wrong setting - just a lot of differrent looks from a variety of controls.


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