7 Replies Latest reply on Mar 6, 2011 3:40 PM by AngLorenzo

    How do the video scopes work?

    AngLorenzo

      And I mean that in a certain technical sense. I know how to read and interpret them but I've come across an issue that I couldn't find any answer to.

       

      It looks like 0 IRE and 100 IRE are mapped to 0 and 255 on the RGB scale and thats fine for color grading or referencing material that goes to the web, but any digital video destined for YUV output is 16-235 (well 235 for nominal white) which comes out to 6.9 and 92 IRE... not exactly marks on the scope scale that are intuitive. Does Premiere map to YUV correctly when burning to tape? Or does it do some voodoo and compress 0-255 to the YUV range? I guess I'm just trying to relate to how it deals with these values.

       

      Currently I'm conforming all of my footage in AE because it's color managed and I can slap on the REC 709 profile and call it a day, but I would love to expand my skill and understanding.

        • 1. Re: How do the video scopes work?
          Jeff Bellune Adobe Community Professional

          Since you mention Rec. 709 in AE, I assume you're using HD footage?

           

          Testing export of color bars and clips with super-white values in an HD sequence from Pr with various codecs and various flavors of YUV, it looks like Pr clips the luma at 100 IRE and at 0 IRE.  Are you seeing something different?

           

          -Jeff

          • 2. Re: How do the video scopes work?
            AngLorenzo Level 1

            Well Jeff, thats the issue. It'll read color bars, but if you export a screenshot of the color bars then black is RGB 0 and white is 255 - there is no "super black" as this is clipped... theres no way to calibrate the scopes or the colorbars to "broadcast legal" versions. I just recently sent this in as a feature request, but I'm trying to confirm for my needs if I'm not blatantly missing someting.

            • 3. Re: How do the video scopes work?
              Jeff Bellune Adobe Community Professional

              I guess I don't understand what you want, or what (if any) issue you're having with Pr.  If we're talking NTSC broadcast video, do you have the Setup (7.5 IRE) box checked on the YC Waveform monitor?

               

              Here's a link to a Bob Donlan article on Premiere's scopes, the Levels filter, and legal NTSC broadcast video:

              Legal Matters « Bob Donlon’s Adobe TV Blog

               

              Beyond that, I can't help.  My knowledge of the subject stops right there.

               

              -Jeff

              • 4. Re: How do the video scopes work?
                AngLorenzo Level 1

                Well not really an "issue", more so seeing if I'm missing something. I suppose let me put it a different way:

                 

                - PPro's scopes use the full RGB scale as its range which makes their scopes not very intuitive to read. Broadcast legal luma on most scopes is 100IRE, on PPro's it's ~92.

                - Final Cut Pro uses the 16-235 scale which maps to YUV (or more accurately YCbCr) which makes it more intuitive to read. Broadcast legal luma reads 100IRE.

                 

                Is there any way (lacking a software feature) to make the scopes behave more like FCP?

                 

                To add to your knowledge, the Setup switch for the 7.5 IRE is irrevelant because the addition of that 7.5IRE gain is only used during transfer to some analog mediums (like VHS), and the switch emulates that boost. But with that in mind, even that setting only reads truly accurate if PPro acted like FCP. This article made it super clear to me: http://www.kenstone.net/fcp_homepage/video_levels_nattress.html

                • 5. Re: How do the video scopes work?
                  Jeff Bellune Adobe Community Professional

                  Sorry; I won't be adding to my knowledge based on how FCP does things.    Any time I see FCP used as a reference, I try to politely bow out of the conversation.

                   

                  -Jeff

                  • 6. Re: How do the video scopes work?
                    Jim_Simon Level 8

                    I get what he's talking about.

                     

                    If you create color bars and look at them on the waveform monitor, black comes out to either 0 or 7.5 IRE depending on the checkbox, and white comes out as 100 IRE.  This is as it should be.

                     

                    But if you export a frame of that, you can see that black is set at 0 RGB, not the correct 16, and white is set at 255 RGB, not the correct 235.  This seems to happen with and without GPU acceleration.  It happens with PNG frame exports or DV exports.  It happens with both SD and HD.

                     

                    It does seem as if Premiere Pro hasn't correctly mapped the video to the RGB scale here.

                    • 7. Re: How do the video scopes work?
                      AngLorenzo Level 1

                      Jeff, as much as I curse FCP... it does do a handful of things right (My favorite saying is that "even a broken clock is right twice a day").

                       

                      But even the Adobe Blog article is wrong.... take a black image at 16 black and put it on the timeline and use the scope (with setup unchecked) and it reads under 7.5... it needs custom mapping