Did NTSC-J always use 0 IRE black level setup?

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NewRisingSun
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Joined: Thu May 19, 2005 11:30 am

Did NTSC-J always use 0 IRE black level setup?

Post by NewRisingSun »

When calculating the NES palette using a NTSC palette generator, the question arises if one should assume a black level of 0 IRE or 7.5 IRE. Clearly, to follow the American NTSC standard, one should go with 7.5 IRE, which darkens the picture a bit. Japanese NTSC on the other hand is said to use 0 IRE setup, and since the NES is a Japanese console, assuming 0 IRE would be the correct thing to do, especially since the RP2C02 PPU does not seem to output black at a higher level than the blanking level.

But! A few websites (such as this one) claim that Japan switched from 7.5 IRE to 0 IRE setup only in 1985. Since the Famicom was released earlier than that, 7.5 IRE setup would then be the correct choice even for the Famicom.

I normally would not give too much credence to a few websites, but I noticed that some of my 1980's Anime VHS and Laserdiscs from Japan seem to use setup as well (black is at around 7.5 IRE, some even higher than that), so there might be some truth to the claim. Of course, bad black levels can always come from bad film transfers as well.

Unfortunately, I could not find any official standards body document that could clear this up. The earliest standards document I could find that mentions Japan is the third revision to Rec. ITU-R BT.470 from 1994, and that one just briefly states in the present tense that regarding the "Difference between black and blanking level", "In Japan values 0 (-0 +10) are used".

Does anyone have additional information regarding the question if or when Japanese NTSC changed from 7.5 IRE to 0 IRE black level setup?
lidnariq
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Re: Did NTSC-J always use 0 IRE black level setup?

Post by lidnariq »

Perhaps the comment about 1985 is that that is when Japan bothered to define a domestic standard at all? And before then it was more ad hoc ?
rocky02009
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Joined: Tue Nov 21, 2023 5:32 pm

Re: Did NTSC-J always use 0 IRE black level setup?

Post by rocky02009 »

I am in China. I used a cheap small TV to test the black level and found that no matter NTSC or PAL, signals below 7.5 IRE will be cut off.
rocky02009
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Joined: Tue Nov 21, 2023 5:32 pm

Re: Did NTSC-J always use 0 IRE black level setup?

Post by rocky02009 »

I have researched commonly used RGB to NTSC conversion chips and believe that the common practice is that the 7.5 IRE up-set is not added during conversion. In other words, assuming the black level of the NTSC signal output by the NES is 7.5 IRE, then the black level of the converted RGB signal is also 7.5 IRE. Vice versa.
Pokun
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Re: Did NTSC-J always use 0 IRE black level setup?

Post by Pokun »

My PVM has a setting for enabling the setup when in NTSC mode. I have it at 0 IRE since all of my NTSC systems are Japanese, but I don't really think there is a difference between the NA and Japanese versions of most video game systems? Even if I play my Famicom on it, I can't tell which one it is supposed to be anyway.
lidnariq
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Re: Did NTSC-J always use 0 IRE black level setup?

Post by lidnariq »

The N64 is entertaining, because earlier revisions (with separate VI-to-RGB and RGB-to-composite chips) use 0IRE, and later revisions use 7.5IRE.

This has no correlation - even a slight anticorrelation due to the later PAL launch - with physical consoles released in each of PAL-B&c, NTSC-J, PAL-M, and NTSC-M.
Pokun
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Re: Did NTSC-J always use 0 IRE black level setup?

Post by Pokun »

Are you saying even PAL N64 systems has the setup? They should all have the later video converter chips, except some French models.
If so my Bergsala N64 model has 7.5 IRE, what a shock! My Japanese 64 is one of those early ones that can be RGB-modded though, so I guess it's 0 IRE.
lidnariq
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Re: Did NTSC-J always use 0 IRE black level setup?

Post by lidnariq »

Yup, that's what I'm saying.
Pokun
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Re: Did NTSC-J always use 0 IRE black level setup?

Post by Pokun »

Heh, that's pretty interesting indeed. :)
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