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  1. Member
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    Does anyone know what the luma level should be on static test patterns? or know how to read a vector/luma scope?

    Please bare with me as I'm not sure I'm asking the correct question, & I need to give a few details in my story.

    I capture analog NTSC video and just bought an Analog Devices EVAL ADV7842-7511 video decoder board for its 3D comb filter. Settings are CVBS-in and HDMI-out at 480i 10-bit 4:2:2 29.97fps.

    I've used many external comb filter devices and have noticed when using Component-out, the image always seems brighter than when outputting via s-video. The image is even brighter with this board.

    Testing with the Video Essentials laserdisc, and using the program that came with the capture card I can view a vector and luma scope. In this particular brightness test pattern the left-most vertical black bar, which is blacker-than-black should be set to the same black level as the background (may be difficult to see here).

    I can adjust the capture brightness of the signal and I've lowered close to what the pattern calls for. I noticed that the value on the luma scope chart falls to around zero when the brightness seems properly adjusted.

    Every capture program is different, but with the default brightness at 0, the luma chart value is about 10 and with the brightness lowered to -8, the luma chart value is 0.

    Question is should certain test patterns yield a luma value of zero when everything is properly adjusted? With different images and patterns the luma value jumps around as expected. It just seems when I adjusted the brightness down to where it's supposed to be, the luma value is zero. So this might be a good indication that I have adjusted correctly?

    Capture card is Osprey 827e and cap program is Ceylon, although I actually cap with VirtualDub but can access Ceylon to adjust color specs.
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  2. For YCbCr black level 0IRE is code value 16, for White 100IRE code value is 235. However U.S. NTSC video colour encoder shifting black level by +7.5IRE, in decoding process this +7.5IRE called pedestal is removed in decoder so 0IRE code value is 16. Problem is if your video decoder works in Japan mode where there is no pedestal thus you may see black level at +7.5IRE.
    It is common problem with NTSC - uncertainty related to pedestal removal - this is video decoder job and it should be done by capture device if properly configured. Trying to fix/correct pedestal after capture will lead to increased quantization noise as re-quantization from 92.5IRE to 100IRE scale is required.

    How to read - it is easy - i think you should move slider to desired line - meter showing single line (at snapshots line 1). To check vertical pattern at once you can rotate video by 90deg so you will see whole pattern shape.
    Last edited by pandy; 21st Jan 2019 at 16:06.
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    Are you saying it's best to capture at the correct YCbCr black level vs. adjusting it in post?
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  4. Originally Posted by clashradio View Post
    Are you saying it's best to capture at the correct YCbCr black level vs. adjusting it in post?
    I'm trying to say that those three vertical bars on left looks like under black, black, just over black for example -2.5IRE,0IRE,+2.5IRE IMHO without touching anything and with correctly set NTSC US you should see only 1 vertical bar +2.5IRE. If you start removing pedestal after capture then you will loose some quality.

    Below example of Pluge signal definition - i think you need to search for description of "your" Pluge signal.
    Click image for larger version

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    check also https://en.wikipedia.org/wiki/Picture_line-up_generation_equipment

    Perhaps SMPTE Pluge will fit your pattern
    Last edited by pandy; 21st Jan 2019 at 18:07.
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    Can I ask how you know the one pluge that you should see has a IRE value of +2.5?

    According to the Video Essentials laserdisc, the left pluge should be even with the black background in the SMPTE pattern, and same goes with "a pluge signal as viewed on a monitor". I'm just eye-balling the slider adjustment.

    Thanks for the ITU link.
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  6. With limited range YUV (Y = 16 to 235, U,V = 16 to 240) everything below Y=16 is supposed to render at the same shade of black as Y=16. You can still see the data on a scope or waveform monitor*. Everything above Y=235 is supposed to render as the same shade of white as 235.

    You generally want to capture with close to the correct levels. As an extreme example supposed you captured so that you only got two Y values, blacks at 234 and whites at 235. You could contrast stretch that to 16 and 235 to restore blacks but you will have lost all the detail between those two levels. So the closer you are to the correct levels the less problems you will have in post.

    * In practice some capture devices may crush blacks below IRE 0 or above IRE 100 (or thereabouts) so you may not see them once the signal has been digitized.
    Last edited by jagabo; 21st Jan 2019 at 21:41.
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  7. Member Cornucopia's Avatar
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    +1 what jagabo said.
    But if you MUST err (please do NOT), err just on the insides of the scale (flatter contrast) and not on the outsides (where you could/would crush/clip).

    Scott
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  8. Originally Posted by clashradio View Post
    Can I ask how you know the one pluge that you should see has a IRE value of +2.5?
    Have no idea but this can be measured - i don't know if NTSC PLUGE standard definition exist as i've saw various PLUGE from +-5IRE to +-2.5IRE, wiki says about PLUGE +-4IRE

    Originally Posted by clashradio View Post
    According to the Video Essentials laserdisc, the left pluge should be even with the black background in the SMPTE pattern, and same goes with "a pluge signal as viewed on a monitor". I'm just eye-balling the slider adjustment.

    Thanks for the ITU link.
    IMHO PLUGE idea is 3 level waveform to quickly adjust capture range - level lower than black (this is possible only in US NTSC where 7.5IRE pedestal exist) then black and then gray just above of black. Now it is tricky to say how properly setup your system - you should see things darker than black or not?
    If your decoder remove pedestal automatically then you should not see things darker than black...
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  9. The pluge is specified in SMPTE RP-219, along with the rest of the color bar signal, as well as explicit instructions on how to set up a monitor (4.3.1).

    http://car.france3.mars.free.fr/HD/INA-%2026%20jan%2006/SMPTE%20normes%20et%20confs/rp...9%20mirehd.pdf

    Below is a .bmp file with pluge patches at 12, 16 (invisible) and 20 per RP-219.

    http://www.chrisnology.info/videos/test_pattern_709.bmp

    7.5 IRE setup became obsolete years ago. Now black is digital 16 which equals 0 IRE.

    Forget Wikipedia. Their representation of SMPTE bars was inaccurate to begin with and the corrected representation was vandalized.

    Note that the primary and secondary colors consist of 16 and 180, e.g. yellow consists of R=180, G=180 and B=16. So-called "SMPTE color bars" have been bastardized and incorrectly explained all over the Internet by people, even software developers, who are ignorant of the actual standard.

    Why this matters is that the test equipment at professional video facilities, those Tektronix scopes that you and I can't afford, is calibrated to RP-219. If you submit content and the color bars are out of spec, in the worst case your content will be rejected. PBS and many of the on-line services such as Netflix are real strict about this.

    Your desktop computer monitor probably doesn't have a brightness control. I solved this by using a TV set with an HDMI input which is fed by my computer's video card. The TV receiver has a brightness control and now I can set up the blacks the way they are supposed to be.
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  10. I'm trying to say that those three vertical bars on left looks like under black, black, just over black for example -2.5IRE,0IRE,+2.5IRE IMHO without touching anything and with correctly set NTSC US you should see only 1 vertical bar +2.5IRE. If you start removing pedestal after capture then you will loose some quality.
    (this is possible only in US NTSC where 7.5IRE pedestal exist)
    No, Pandy. 7.5 IRE for U.S. video went out the window years ago. Blacks are 0 IRE (digital 16) in the U.S., Japan and almost everywhere else.

    In 2019 7.5 IRE = digital 32 and we know this is wrong. Per BT.709 black = digital 16.

    Really, you know better than that.
    Last edited by chris319; 6th Mar 2019 at 05:29.
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  11. Originally Posted by chris319 View Post
    Note that the primary and secondary colors consist of 16 and 180, e.g. yellow consists of R=180, G=180 and B=16.
    Thats for limited range RGB (used for creating pluge patterns). What is normally viewed on the screen by the end user is full range RGB where the primaries are 0 and 191. The conversion from YUV to RGB normally handles this.
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    Originally Posted by pandy View Post
    I'm trying to say that those three vertical bars on left looks like under black, black, just over black for example -2.5IRE,0IRE,+2.5IRE IMHO without touching anything and with correctly set NTSC US you should see only 1 vertical bar +2.5IRE.
    This.

    And after you have everything lined up, be prepared to mess with the Osprey image controls because tapes will be all over the place, to say nothing of how your VCRs are calibrated.
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  13. Originally Posted by jagabo View Post
    Thats for limited range RGB (used for creating pluge patterns). What is normally viewed on the screen by the end user is full range RGB where the primaries are 0 and 191. The conversion from YUV to RGB normally handles this.
    No, it's for compliance with SMPTE RP-219. As I explained earlier, the waveform monitors and vectorscopes in a professional video facility are calibrated for RP-219. Anyone who has worked in a professional facility for 5 minutes knows this. I'm talking about professional video distributed in YUV such as broadcast or on-line distribution to the public via Netflix, etc. As I also explained earlier, if your bars are out of kilter your content is likely to be rejected and they won't accept ignorance of the standard as an excuse.

    If you're talking about amateur video from Joe YouTube User or are only interested in viewing on a monitor or cinema screen and don't care about interchangeability, you probably don't even need color bars or care about video levels.

    You would benefit from reading the standard.
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    Originally Posted by chris319 View Post
    No, Pandy. 7.5 IRE for U.S. video went out the window years ago.
    Not if you're capturing analog NTSC video, which is what this thread is about.
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  15. Originally Posted by chris319 View Post
    I'm trying to say that those three vertical bars on left looks like under black, black, just over black for example -2.5IRE,0IRE,+2.5IRE IMHO without touching anything and with correctly set NTSC US you should see only 1 vertical bar +2.5IRE. If you start removing pedestal after capture then you will loose some quality.
    (this is possible only in US NTSC where 7.5IRE pedestal exist)
    No, Pandy. 7.5 IRE for U.S. video went out the window years ago. Blacks are 0 IRE (digital 16) in the U.S., Japan and almost everywhere else.

    In 2019 7.5 IRE = digital 32 and we know this is wrong. Per BT.709 black = digital 16.

    Really, you know better than that.
    No, no, no - digital black is always 16 - digital (analog?) NTSC encoder shifts black by adding 7.5IRE DC bias - It is very wrong to count 7.5IRE pedestal to digital data (this prevent for example transborder exchange - materials between Europe and US don't need to be adjusted as 16 and 235 are delivering always black and white) - pedestal is created at the output by additional circuitry. Also capture device should automatically detect pedestal and remove it before outputting data (and 7.5IRE IMHO was tailored to save RF transmitter power or perhaps to transmitter to push peak output power of the RF amplifier as video was broadcasted as negative AM modulation - darker received higher power - sync tip receive 100% power, by shifting video this can reduce average power more so amplifier may try to operate in non linear/saturated part for sync (something like class C) - same as 8-VSB - for US transmission range was very important - large country, large area to cover with RF signal, if you can save few tens of kW (RF amplifier operate with hundreds of kW).
    Commonly in digital composite NTSC encoder this is done by adding in digital adder circuit to incoming from video data, digital values representing sync pulses and pedestal and feeding this to for example 10 - 14 bit DAC to create linear analog signal - this is very convenient way of dealing with signal in digital domain. Look at this for example https://opencores.org/projects/graphiti - not the best DENC but is shows how things are done.
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  16. Member Cornucopia's Avatar
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    If it says "IRE" it's supposed to be analog. So don't confuse the two.
    Also, Analog BROADCAST went out the window, not analog video in general. There is still plenty of analog video out there, and will be for years to come.

    In analog land,
    0 IRE=Black everywhere except US NTSC, where it has been 7.5 IRE due to setup/pedestal.
    100 IRE = White EVERYWHERE.

    In digital (8bit) land,
    Y 16 = Black EVERYWHERE
    Y 235 = White EVERYWHERE
    unless you converted to PC Full setting, which is Y=0...Y=255, but that is totally NON-STANDARD with regard to analog conversions or pro video.

    Scott
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  17. If it says "IRE" it's supposed to be analog. So don't confuse the two.
    IRE units are used in digital. 0 IRE = digital 16; 100 IRE = digital 235.

    Analog BROADCAST went out the window, not analog video in general. There is still plenty of analog video out there, and will be for years to come.
    There are still low-power BROADCAST stations transmitting analog.

    Although Congress established a hard deadline of June 12, 2009, for full power TV stations to cease analog broadcasts and begin operating only in digital, and the Commission set a transition date of September 1, 2015, for Class A television stations to complete their transition, neither of these deadlines applied to low power television stations or TV translator stations (referred to herein as "LPTV stations"). Therefore, although all full power and Class A television stations have ceased over-the-air analog broadcasting, LPTV stations are continuing to transmit analog signals.
    https://www.fcc.gov/consumers/guides/low-power-television-lptv-service

    7.5 IRE setup was added as a buffer zone. If black were 0 IRE without setup, excursions below black might bother sync circuits. In digital this is why black and white are 16 and 235 and not 0 and 255. In ATSC, 0 and 255 are the sync levels.
    Last edited by chris319; 6th Mar 2019 at 16:05.
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  18. Member Cornucopia's Avatar
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    Originally Posted by chris319 View Post
    If it says "IRE" it's supposed to be analog. So don't confuse the two.
    IRE units are used in digital. 0 IRE = digital 16; 100 IRE = digital 235.

    Analog BROADCAST went out the window, not analog video in general. There is still plenty of analog video out there, and will be for years to come.
    There are still low-power BROADCAST stations transmitting analog.

    Although Congress established a hard deadline of June 12, 2009, for full power TV stations to cease analog broadcasts and begin operating only in digital, and the Commission set a transition date of September 1, 2015, for Class A television stations to complete their transition, neither of these deadlines applied to low power television stations or TV translator stations (referred to herein as "LPTV stations"). Therefore, although all full power and Class A television stations have ceased over-the-air analog broadcasting, LPTV stations are continuing to transmit analog signals.
    https://www.fcc.gov/consumers/guides/low-power-television-lptv-service

    7.5 IRE setup was added as a buffer zone. If black were 0 IRE without setup, excursions below black might bother sync circuits. In digital this is why black and white are 16 and 235 and not 0 and 255. In ATSC, 0 and 255 are the sync levels.
    Yes, we know why 7.5 setup was added. Water under the bridge.

    Yes, we know there are a few LPTV stations, but basically nobody is counting them. Certainly not you, who said in the earlier post that it went out the window. Regardless, my point there was that it doesn't matter about broadcasting, because some elements of analog video recording and playback are still with us for the present, and so still is 7.5 setup. I think you knew that and were just trying to obfuscate.

    But, look up IRE, it historically refers to Composite Analog Video.
    That xx IRE = yy digital Y is an equivalency. Thus 100 IRE = Full White, Full White = 235 Y, and by transitive property 100 IRE = 235 Y.

    Scott
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  19. Originally Posted by Cornucopia View Post

    Yes, we know why 7.5 setup was added. Water under the bridge.

    Yes, we know there are a few LPTV stations, but basically nobody is counting them. Certainly not you, who said in the earlier post that it went out the window. Regardless, my point there was that it doesn't matter about broadcasting, because some elements of analog video recording and playback are still with us for the present, and so still is 7.5 setup. I think you knew that and were just trying to obfuscate.

    But, look up IRE, it historically refers to Composite Analog Video.
    That xx IRE = yy digital Y is an equivalency. Thus 100 IRE = Full White, Full White = 235 Y, and by transitive property 100 IRE = 235 Y.

    Scott
    Yes, some analog NTSC video is still around.

    Did you have another point to make?
    Last edited by chris319; 6th Mar 2019 at 16:56.
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  20. Member Cornucopia's Avatar
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    The point that IF one continues to have to deal with analog US NTSC video (capturing, transferring, processing), one will continue to have to account for NTSC 7.5 IRE setup. And it should especially be done BEFORE the point of digitization.

    The other point being the OP was quite satisfactorily answered prior to your muddying detour. I donít think, or I sure hope, that wasnít your intention, but thatís what it amounted to. The OP made it clear in the 1st post that they were working with analog US NTSC sources and reference material.

    Scott
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  21. Originally Posted by Cornucopia View Post
    If it says "IRE" it's supposed to be analog. So don't confuse the two.
    Also, Analog BROADCAST went out the window, not analog video in general. There is still plenty of analog video out there, and will be for years to come.

    In analog land,
    0 IRE=Black everywhere except US NTSC, where it has been 7.5 IRE due to setup/pedestal.
    100 IRE = White EVERYWHERE.

    In digital (8bit) land,
    Y 16 = Black EVERYWHERE
    Y 235 = White EVERYWHERE
    unless you converted to PC Full setting, which is Y=0...Y=255, but that is totally NON-STANDARD with regard to analog conversions or pro video.

    Scott
    IRE is North America (and perhaps Japan - not sure on this but Japan is on safe side as they don't use pedestal) unique unit - in Europe nobody use IRE (but IMHO every video engineer knows IRE) - Europe use % instead IRE, where 0IRE = means 0% of nominal 700mV signal (i.e. 0 IRE=0%=0V) and 100% means 700mV (once again i think using IRE is more convenient/human friendly in US where 100% signal is 714.3mV). I agree with you on this - 16=Black and 235=White is everywhere by standard.
    Problem with pedestal begin in capture if your HW is unable to remove pedestal before digitalization and later captured data are output as 8 bit or if 8 bit ADC is used to capture signal and later trough digital processing pedestal is removed. Those two cases will produce suboptimal conditions for signal capture as we loose signal data.
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  22. The OP made it clear in the 1st post that they were working with analog US NTSC sources and reference material.
    This point has been made several times in this thread. Are you going to belabor it any further?
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