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Black Level ?

post #1 of 14
10/31/09 at 1:30pm
Thread Starter 
It's been a while since I've thought about this & have a question.
Analog North American NTSC video has the black level at 7.5 IRE.
Digital video has the black level at 0 IRE for all countries.

What about component video? YCrCb is digital component and YPbPr is analog component. Does the video industry differentiate between the two & set YCrCb at 0 IRE black and YPbPr at 7.5 IRE black?

If so, then a typical Comcast Motorola DVR outputs HDMI black at 0 IRE and analog YPbPr component black at 7.5 IRE, is that correct?
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post #2 of 14
10/31/09 at 8:24pm
AIUI - and I may be wrong - the 7.5IRE black level is only technically valid for 480i NTSC composite/S-video and possibly 480i component.

AIUI 480p YPrPb component and above should all have black level at 0IRE - as the rest of the world does for all analogue video. HD video - 720p and 1080i should have no 7.5IRE set-up AIUI.

(Japan uses 0IRE with their analogue NTSC - 7.5IRE set-up really is a North American thing)

There have been a number of different standards for 480i/576i YPrPb levels in the past - ISTR that the early Beta SP (and MII?) VTRs I came across had labels detailing whether they had EBU component levels (versus other standards)?

My (no doubt flawed) memory is that analogue component outputs shouldn't have 7.5IRE set-up - but that some implementations may have?
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post #3 of 14
10/31/09 at 10:49pm
Thread Starter 
sneals2000,

Thanks for the reply. Once in a while I think about getting a component > S-video converter to use with my Comcast Motorola DVR. The DVR letterboxes the S-video output which I need to use if I want to record a program connected to my stand alone DVDR. From what I can tell, some converters only work with 480i but others work with several resolutions.

I emailed the supplier and asked about black level but never received a reply. If a converter is going to screw up the black level then no sense even trying it.

I'm getting mixed signals, no pun intended, when I tried to research the Internet about YPbPr black level. Articles typically talk about the differences and to make sure that you set up your equipment properly. But I did not find anything regarding an official spec.

Thanks again.
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post #4 of 14
11/1/09 at 9:46am
The EIA/CEA 770.2 consumer standard calls for 0% setup (black level) on YPrPb component video. A converter to S video should have the option to add 7.5% setup. Alternately the devices using the S video may have an option of using 0% setup.

My guess is that a STB is not adding setup as it's creating the analog from digital signals. I'll qualify this as a guess as I haven't seen definitive proof.
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post #5 of 14
11/1/09 at 10:10am
Quote:
Originally Posted by sneals2000 View Post

There have been a number of different standards for 480i/576i YPrPb levels in the past - ISTR that the early Beta SP (and MII?) VTRs I came across had labels detailing whether they had EBU component levels (versus other standards)?

My (no doubt flawed) memory is that analogue component outputs shouldn't have 7.5IRE set-up - but that some implementations may have?

There are differences in the chroma levels for the Beta and SMPTE standards for SD YPrPb. From what I was reading the Panasonic MII format may have used setup on the Y channel. In the US NBC was the only major network to use MII and I never heard many complementary words regarding that format. NBC is pretty much all Sony for production tape format and cameras.
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post #6 of 14
11/1/09 at 11:40am
Quote:
Originally Posted by TVOD View Post

There are differences in the chroma levels for the Beta and SMPTE standards for SD YPrPb.

Yep - I suspect the labels I was noticing were differentiating between Sony and EBU levels (I suspect the EBU and SMPTE levels were the same?)

Quote:


From what I was reading the Panasonic MII format may have used setup on the Y channel. In the US NBC was the only major network to use MII and I never heard many complementary words regarding that format.

Over here MII was used by at least two of the ITV franchises (now almost all merged) for local news. (Thames and Anglia). I was working in the Anglia region at the time and the BBC used Beta SP. It made sharing footage a total pain (as one or other operation had to hire a machine for the other format...)

The BBC (and NBC - and I think NHK) were also the main purchasers of the D3 1/2" digital composite format ISTR...

Quote:


NBC is pretty much all Sony for production tape format and cameras.

The BBC is pretty much universally Sony in studios (BVPE30 SD cameras and DigiBeta VTRs, HDC1500s HD cameras and HDCam/HDCam SR VTRs) - with a few Thomson 1657s and LDK100s still kicking around in the older un-refurbished 16:9 SD first generation studios. (Most 1657s have been replaced by E30s or HDC1500s)

On location Panasonics DVCPro HD is pretty popular as an aquisition format (as it is 1440x1080 at 25/50Hz, unlike the 1280x1080 30/60Hz variant) for low-to-mid range HD, with Sony DVCam (DSR 450s and upwards) popular for SD and for News. Both of these are relatively open formats - which is increasingly important these days.

HDCam SR and DigiBeta are the industry standard HD and SD delivery formats though in the UK pretty much - both Sony proprietary formats.
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post #7 of 14
11/1/09 at 2:48pm
Mike99, I'm not sure what kind of DVDR you have, but Panasonic DVDRs have a black level input adjustment. It's in the FUNCTIONS, SETUP menus. It allows 2 settings, NORMAL and DARKER. I personally use DARKER for recording from my CM-7000 CECB via S-video. Panasonics also have 2 settings for COMPONENT output, NORMAL and DARKER, I use normal for my one Panny that doesn't have HDMI output and I use component output.
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post #8 of 14
11/1/09 at 5:43pm
Thread Starter 
TVOD,

My HDTV does not have any way to select black levels, therefore even the lowly 480i must be using the same levels as 1080i. And selecting the output resolution on the Comcast DVR does not appear to affect the black level when viewed on the TV using a component connection.

I could feed a converter a 480i signal since it's going to end up at 480 anyway in order to record it with a stand alone DVD recorder. This may save a bit of picture quality since an inexpensive converter would not have to rescale the signal. Now the question is how does the converter affect the S-video output black level.

jjeff,

I have two Panasonic DVDRs & they do have adjustable black levels. Long time ago I played with them and set them back to the default settings which looked correct, at least for me. Neither of these have HDMI so I use component. Of course I could change a setting if need be when using a converter.

The Converter -

Thanks to kjbawc and jjeff in the DVD Recorders forum for the link.
http://www.dealextreme.com/details.dx/sku.22844

This converter, or ones that look like it, is sold by a few vendors. I thought I had an English link to the manufacturers web but do not. BTW, this is not the product that I had asked about black levels. This Lenkeng seems to be the least expensive converter out there and appears to work with many input formats.

It does not look like it has any switch selectable setting for black level. Of course I don't expect a lot considering the price. Since the converter is made overseas they may not even know that North America sometimes uses a different black level and therefore did not make it selectable.

Is it safe to presume that since S-video is not digital that it's black level in North America is different than in Japan?
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post #9 of 14
11/1/09 at 7:39pm
I assume that Japanese S Video doesn't use setup while the North American standard does. S Video is really composite video with separate paths for Y and C. One can y them together into an unterminated video input and the two sources (Y&C) will terminate each other.

The darker mode from what I've read is the 0% setup setting. If the CAV to S Video converter doesn't have a black level selection it may just pass the Y channel as is (with delay) and encode the chroma channels.
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post #10 of 14
11/2/09 at 2:19am
Quote:
Originally Posted by TVOD View Post

I assume that Japanese S Video doesn't use setup while the North American standard does. S Video is really composite video with separate paths for Y and C. One can y them together into an unterminated video input and the two sources (Y&C) will terminate each other.

That is my understanding - no set-up on Japanese NTSC, whether composite or S-video.

Quote:


The darker mode from what I've read is the 0% setup setting. If the CAV to S Video converter doesn't have a black level selection it may just pass the Y channel as is (with delay) and encode the chroma channels.

Yep - either it permanently adds the 7.5IRE set-up or it doesn't!

I'd expect any TV with a black level setting to be switching 7.5IRE set-up removal in and out. (Though if one setting appears darker than the other - wouldn't the darker setting be the 7.5IRE setting, as it will be removing the 7.5IRE set-up. If you feed this with a 0IRE feed you'll be crushing blacks?)

Thinking back - my first DVD player (a Samsung which would output DVDs both natively in PAL/RGB 50 and NTSC/RGB 60 for multistandard displays as well as optionally convert between 480i and 576i allowing permanent PAL/RGB 50 or NTSC/RGB 60 output for non-multistandard displays) - had a menu option to add 7.5IRE set-up to its video outputs - presumably for North America?
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post #11 of 14
11/2/09 at 4:39am
Of course the whole purpose for setup was for early TV's that couldn't handle 0 IRE black and caused them to do nasty things to the picture since it confused 0 IRE with the sync pulse. Setup has been an outdated spec for 50 years for NTSC and I celebrate its death in the digital age.
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post #12 of 14
11/2/09 at 8:24am
I thought the setup was to minimize the chance of getting retrace lines. By having the blanking lower than black I suppose it would be possible to get away with not having active blanking at all. I suspect it was one of those precautions that turned out to be unnecessary, much like the .1% reduction of scan frequency was done in case of beats between the sound and color subcarriers.
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post #13 of 14
11/2/09 at 3:24pm
Quote:
Originally Posted by foxeng View Post

Of course the whole purpose for setup was for early TV's that couldn't handle 0 IRE black and caused them to do nasty things to the picture since it confused 0 IRE with the sync pulse. Setup has been an outdated spec for 50 years for NTSC and I celebrate its death in the digital age.

I don't think that the earlier British 405 line system (in used in the UK since 1936 - with a break during the war) had black level set-up (though I may well be wrong)? Wouldn't you be looking for edge excursions below 0IRE for syncs?

That said, ISTR that it wasn't uncommon for video whizzing around 405 line studios to be without any syncs (on the assumption that everything was sync locked -which must have made timing stuff a bit fun...?)
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post #14 of 14
11/3/09 at 7:49am
Quote:
Originally Posted by sneals2000 View Post

I don't think that the earlier British 405 line system (in used in the UK since 1936 - with a break during the war) had black level set-up (though I may well be wrong)? Wouldn't you be looking for edge excursions below 0IRE for syncs?

Or more specifically transitions in the least positive part of the signal as video was commonly capacitive coupled and clamped, typically with a diode (I don't think feedback clamps were popular yet )

As for timing issues without sync pulses, it probably wasn't an issue as there likely were no timing adjustments like genlock phase. In fact it may have made things easier as black clamping could occur anywhere in the blanking inverval without having to be concerned about sync which required back porch clamping. Reference pulses were discrete until black reference became popular. This required H & V drive, sync, blanking and later subcarrier to all be distributed in parallel. Color encoders did have subcarrier phase adjustments. Later on it was common practice to external reference the downstream proc amp to ensure proper SCH phase, especially in edit suites. I wonder how many people working in TV now know what color framing is (my favourite part of PAL).

Ah the good 'ol days right after the planet thawed out.
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