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PostPosted: Fri Aug 18, 2017 10:15 am 

Joined: Thu May 19, 2005 11:30 am
Posts: 653
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?

PostPosted: Fri Aug 18, 2017 7:13 pm 

Joined: Sun Apr 13, 2008 11:12 am
Posts: 7532
Location: Seattle
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 ?

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