3 Replies Latest reply on Jan 3, 2011 12:54 AM by Sengstack

    7.5-100 IRE still valid?

    Sengstack Level 1

      If a video is destined to be viewed on a PC monitor, an NTSC TV set via a DVD player, HD via Blu-ray, or HD via broadcast (cable, satellite or antenna), is setting the black level to 7.5 IRE and the white level to 100 still valid?

       

      The P Pro Help file notes in a couple places that it's good to use a 7.5 IRE black level to ensure levels are within broadcast standards. But, most videos made these days are not for broadcast. And, as I understand it, we're talking only NTSC broadcast for North America standard definition TV sets (Japan NTSC standards allow for 0 IRE). What about HD broadcasts? And 7.5 IRE translates to lightened shadows.

       

      On the other end of the scale, what about 100 IRE for white output? 100 IRE translates to something darker than pure white in the RGB space of PC monitors.

       

      The P Pro Waveform monitor will not let you raise the white levels past about 107 IRE (the scale goes to 120). And you can't lower the black levels below -8 or so (the scale goes to -20 IRE).

       

      In any event...should video editors set different Black and White IRE levels depending on the playback platform?

       

      Jeff Sengstack

        • 1. Re: 7.5-100 IRE still valid?
          Jon-M-Spear Level 4

          My understanding is not so much whether playback is for an LCD or conventional CRT monitor (as that may be out of the broadcaster's control), but whether it is an anlogue or digital signal.  IRE is only relevant in the analogue domain.

           

          With analogue, NTSC pedestal is 7.5 IRE (black) and 100 IRE (white).  PAL = 0 and 100

           

          DV follows ITU-R Rec. 601  and stores video in Y'CbCr.  As such, the Y' (luma) levels should be set at 16 RGB (black) and 235 RGB (white).

           

           

          See:

           

          http://help.adobe.com/en_US/premierepro/cs/using/WSCE1EF46C-AB40-45f9-BAD8-D790421BD01A.ht ml

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          • 2. Re: 7.5-100 IRE still valid?
            Sengstack Level 1

            This is a wrinkle I hadn't considered. So pardon me for asking a couple follow-up questions:

             

            Is it correct to say that these days all TVs (CRT or LCD) receive signals via cable, satellite or antenna which, I think, are all digital. So IRE 7.5 does not apply to them?

             

            If so, what is delivered via analog these days? Not much I'm guessing. So, are you saying that IRE 7.5 is irrelevant?

             

            To clarify the other point you made: DV, by virtue of its color space, needs levels of 16 and 235 set as the last step before final output to ensure a full contrast ratio in digital playback. Correct?

             

            What about HD (ITU-R BT.709) or RED?

             

            Thanks.

             

            Jeff

            • 3. Re: 7.5-100 IRE still valid?
              Jon-M-Spear Level 4

              It's hugely complex but it's largely about the origins of the SOURCE material; analogue or digital, rather than how the material is to be viewed (there are a huge amount of caveats to that statement, but I won't linger!!!).

               

              BetaSP is analogue, for example, and Red is digital.  However, they're both digital once they're been converted to an NLE system, and either could be played back on a CRT or LCD monitor, so the replay device is a red herring (so to speak).

               

              Waveform monitors embedded in NLE editing applications are notoriously bad with digital material.  It is an analogue tool.  built-in NLE waveform monitors cannot determine the accuracy of the analogue>digital conversion.  Therefore, they do not have a correct black/white reference point.  The black pedestal is only the waveform monitor's interpretation of where it thinks 0/7.5 IRE should be.

               

              As a general rule of thumb for setting digital levels; set your preview/program monitor black and white levels and chroma accurately using the NLE's colour bars. Once these are correctly calibrated, use the Y'CbCr parade to double-check RGB levels (16 and 235).

               

              Obviously, certain networks may have specific requirements.  When I produce video for conference play-in, I always check with the Technical Producer whether he wants it output to a particular spec.   However, by following the above guidelines during the edit, you will have material of consistent quality (levels etc) in your sequence  - to which global adjustments can be made, if required.