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Old 05-09-2012, 01:30 AM - Thread Starter
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I would like to know more about black levels.

Is the 7.5 IRE spec actually part of the NTSC signal on the source DVD/VHS/LD or is the 7.5 IRE added to the NTSC signal by the device that is outputing the signal, in this case a DVD/VHS/LD player?

If i had a PAL player that can play NTSC tape/disc at the original 3.58 spec (not conversion to 4.43) will this output the NTSC singal with 7.5 IRE or not because my player is PAL? In the latter case, would it mean that although playing it as 3.58 it wont be outputing the NTSC video with the correct black level?

If its the playing device that 'adds' the 7.5IRE to the NTSC signal, does that mean i would better off to use a native NTSC device that 'adds' the 7.5 IRE so that the black level is right if my PAL device only plays NTSC 3.58 but not with the correct black level?
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Old 05-09-2012, 05:54 AM
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Here's a great article on black level that describes the problems we see, how analog and digital black levels are often confused, effects on calibration discs, PAL/NTSC differences, etc.

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Old 05-09-2012, 06:22 AM
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Another good thread talking about black levels:
http://forum.videohelp.com/threads/201765-IRE-settings
From what I understand 0 IRE is the standard for DVD, N. American players add +7.5 IRE to their SD outputs to conform to the standard of our TVs line inputs. Not positive about VHS(or video tape in general) but my guess is the actual analog signal may be +7.5 on the tape for N. American use but I bet one of the two links say for sure.
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Old 05-09-2012, 07:14 AM - Thread Starter
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Off to read those articles above now
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Old 05-09-2012, 01:08 PM
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Here's some more info. It discusses using AviSynth with VideoScope to display the luma values. I was having a problem with washed out blacks in this example.

http://forum.videohelp.com/threads/2...TV-Safe-Colors

Later I used VideoScope because blacks looked crushed when recording with a Magnavox DVD recorder and VideoScope verified this. It did take a bit of time to do this but it is interesting to see what the actual levels are.
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Old 05-09-2012, 08:58 PM - Thread Starter
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Well i have not finished reading all those articles but i just started getting totally confused by it all, way over my head, and it was only getting worser. I could not even say if its only DVD affected by this or VHS too? or if if the 7.5IRE is added by the machine or is present on the disc/tape.
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Old 05-09-2012, 11:08 PM
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I used to know the answer to this but can't remember without checking some reference. I think what jjeff said is correct.

jjeff wrote: From what I understand 0 IRE is the standard for DVD, N. American players add +7.5 IRE to their SD outputs to conform to the standard of our TVs line inputs. Not positive about VHS(or video tape in general) but my guess is the actual analog signal may be +7.5 on the tape for N. American use

I think that's right but Cyclone should do research to confirm.

I don't like the article jjeff posted though. I quit reading it after a few sentences because of this.

Blame lazy engineers from a long time ago. Because of this, all of our equipment is different from Japanese stuff.

That is not true and the poster did not do his research. The 7.5 IRE set up was there for a reason. Can't remember exactly why but it had something to do with setting up broadcast and production gear. I believe the Japanese used the 7.5 IRE until equipment got better for set up and you didn't need it anymore. That's just me from memory, not researched fact.
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Old 05-10-2012, 07:14 AM
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Quote:
Originally Posted by Super Eye View Post


“””Blame lazy engineers from a long time ago. Because of this, all of our equipment is different from Japanese stuff.”””

I agree, that quote isn't very professional but like most everything else from a forum it wasn't written by a professional but rather people like you and I. You kind of have to take the bad with the good. Overall the thread contains some valuable information but as you pointed out it also contains some "opinions" which may or may not be correct. I also believe Mike99's thread contains a lot of valuable information but like Cyclone82, most of it is over my head and somewhat confused me more than not
To answer Cyclone82's question, from re-reading the thread it looks like tape(or analog for N. America in general) is stored as +7.5 IRE. As long as your TV is calibrated for that you'll get good black levels. If your TV is calibrated for the rest of the world and you play back such a tape your image will be too light. The opposite is true for playing a non N. American tape on a N. American TV, the image will be slightly dark.

I believe to avoid part of the problem these different standards caused, when DVD came along N. America went along with 0 IRE on the actual DVD but to retain compatibility with older equipment the players needed to add 7.5 IRE to their SD outputs. At the same time?? when HD outputs came along N. America took the advantage to get with the rest of the world and use a 0 IRE level for everything(input, storage and output). Note my last sentence is just what I'm speculating makes sense, their could be other reasons we changed to 0 IRE but what I said makes sense to me, I'm open to corrections.
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Old 05-10-2012, 07:26 AM
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As that article linked in Post #2 says:

On the internet, there is a lot of confusion concerning "7.5 IRE setup". A great deal of this confusion arises because the issue can be confused as a single problem. The problem can be seperated into the following issues:

-Not all equipment follows engineering standards. Most DV equipment fails to covert from digital to analog properly.

-Confusing terminology. In some articles, analog units are erroneously used to describe digital levels.

-Fake digital setup. Some equipment can try to compensate for the setup problem by recording non-standard levels.

-Confusing settings labelled 7.5 IRE. The waveform monitor and vectorscopes in some editing applications try to simulate analog levels. Because the software does not know your analog levels, you have to tell the software what your levels are in order to achieve a correct simulation.

This article will try to clear the confusion and misconceptions concerning 7.5 IRE setup.

To understand the issue, it first helps to understand what your video levels should be (i.e. the standard levels).

Analog - composite Digital - DV, DVD (8-bit formats)
  Black Level White Level Black Level White Level
NTSC (except for Japan) 7.5 IRE 100 IRE 16 (Y') 235 (Y')
NTSC (Japan) 0 IRE 100 IRE    
PAL 0 IRE 100 IRE    

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Old 05-10-2012, 10:40 AM
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I *THOUGHT* I understood this problem, until this thread. Now I am really in the dark/light/dark about it.

Luke

Evil is charming and beautiful. It makes you doubt yourself. It asks for one small compromise after another until it whittles you down, and it functions best when no one believes in it.-JOA
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Old 05-10-2012, 03:47 PM
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Quote:
Originally Posted by wajo View Post

As that article linked in Post #2 says:

On the internet, there is a lot of confusion concerning "7.5 IRE setup". A great deal of this confusion arises because the issue can be confused as a single problem. The problem can be seperated into the following issues:

Wajo, do our Maggys have any hidden IRE setup available?
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Old 05-10-2012, 03:58 PM
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Quote:
Originally Posted by profhat View Post

Wajo, do our Maggys have any hidden IRE setup available?

I'm not sure... there's no mention of "black level" or "lighten" in the manual and nothing in menus, but there is the HDMI > RGB Mormal/Enhanced setting (mentioned here) that does seem to affect brightness.

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