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Activity Forums DaVinci Resolve Low luminance levels: what are mv values and how to adjust them (in DaVinci)?

  • Low luminance levels: what are mv values and how to adjust them (in DaVinci)?

    Posted by Wilfred Lovell on May 22, 2023 at 9:03 pm

    Hi,

    I have been asked to provide a video according to broadcast standards. The file failed QC due to low (luminance) levels, more precisely because of 0.5 mv instead of 0.7 mv for a few shots.

    I’ve been playing around with the scopes a bit, but to be honest I’m a bit lost.

    Any idea what they want exactly? I’m not quite sure what the mv values are and how to adjust/fix them.

    Thanks!

    Michael Gissing replied 10 months, 2 weeks ago 3 Members · 6 Replies
  • 6 Replies
  • Riccardo Luppi

    May 24, 2023 at 6:54 am

    Hey mate, what you should do is grade normally, export you file in 10but 422 and re-import it in DaVinci. Then go into your settings, colour management, and check the “broadcast legal” checkbox at the bottom of the page.

    Then re-export the file to whatever format the network required.

  • Wilfred Lovell

    May 29, 2023 at 11:21 am

    Hi Riccardo!

    Thank you very much for your answer!

    Actually about the Broadcast color safeness I was aware before I delivered the file to the Broadcaster. I exported it according to IRE 103 (SMPTE) … so i thought Im gonna be fine.

    But it seems they are complaining about a few explicit talking head shots … these shots are bit dark but its more a lightning production issue. Anyways the Broadcaster cant except it that way and I think I need to increase the brightness for a few scenes. I am myself a full-time video editor but have to admit my color grading skills are a bit limited.
    I would just like to know how to adjust these MV values (and what exactly are MV values anyway?!). And where to adjust them in davinci?

    Im thankful for any reply!

  • Riccardo Luppi

    May 29, 2023 at 6:13 pm

    Hey mate, so the mV are a scale that little has to do with how we normally describe luminance in film. it refers to the voltage of the signal acquired by the sensor. That said, the 0.7mV refers to the black level they are expecting, but they should have a sheet that states also the IRE level they are expecting. That is what you should ask. Cause once you have that, you can set a line in your waveform at that value and simply make sure that nothing goes below it.

  • Wilfred Lovell

    May 29, 2023 at 8:32 pm

    Hi Riccardo,

    first of all: I really appreciate your help!! 😊

    There is a screenshot attached of one of the scenes the broadcasters complains about. I checked it with the scopes and if I understand it correctly, the black levels are actually clipped.

    Also I set the scale (y-axis) [waveform scale style] to mV – so it shows me 0 mV (being black) to 700 mV (white).

    In my naiveté and stupidity, I tried to set my (low) reference levels to 0.7 mV – which, hoever, makes no sense at all with a scale of 0 – 700 mV. Because in this case, the line for low reference does not move at all …

    Excuse my lack of knowledge, I am a full time video editor and cutter but regards color grading I often reach my limits …

    Cheers!

    W.

  • Wilfred Lovell

    May 29, 2023 at 8:55 pm

    Hey Riccardo 😉

    So I thought a little bit further … and now I understand your hint regarding the IRE values … if I set the scale to percentage (IRE) … then I can work with a specified percentage value rather I can set my low reference line to that percentage value. And then adjust the color wheels (Lift)? Do I undestand this correctly?

    Thanks again

    W.

  • Michael Gissing

    May 31, 2023 at 2:34 am

    The important thing is how to make the images look good and be broadcast compliant. Worry less about the waveform as that is just a tool for compliance to troubleshoot. Without seeing the image it looks like there are some very bright spectral highlights in your otherwise dark image. Increase gain and gamma with the color wheels or try pushing up brightness with curves. You can trim back the highlights or let them clip, depending on what it looks like. Highlight trimming can be done with curves, the highlight adjustment on the color wheels or the HDR color tool. The tech reject might talk about Mv and IRE levels but in the end it is what the image looks like. Resolve will clip to broadcast spec

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