17 Replies Latest reply on Mar 22, 2010 3:44 AM by mshushan

    Green Screen using AVC-Intra 100 ugly

    mshushan

      Been using the hpx300 for approx two months mostly in 720p with great results. Just wraped our first true HD green screen shoot using avc-intra 100 at 24p with the intent of producing a white background mac-ad type, 5 min talking head corporate piece in SD. I had the camera mounted at 90 degrees to capture the 1920 pixels of subjects head-to-toe so I could then manipulate individual zoom and placement in post within a SD timeline. I've got two issues: one is that the images in post seem noisy, and any movement, as in subjects walking across screen, is a total mess - I say seem because all recording and playback on location looked just fine on a 1920x1200 monitor via blackmagic i/o box. I normally do basic editing in premiere with much help from AE for composting and color correction etc. Keylight has always worked great in the past. I must have something wrong with settings in the avc-intra HD content? Secondly, workflow is a bit convoluted... Keylight doesn’t apply in premiere, and AE doesnt do avc-intra. The workaround is to export avc-intra premiere timeline to AE and key that.  In theory it should work just fine, but again my images are just noisy. Could this PR to AE workflow degrade image quality?  Any suggestion greatly appreciated! Thanks, Matt

        • 1. Re: Green Screen using AVC-Intra 100 ugly
          Level 4

          Hi,

           

          I've read that HD is not a good format for greenscreen in some circumstances.... and also that 24fps is not good generally...because in the case of having marks on the greenscreen ( for camera match moves specifically ) any " blur " will lose the lock on those marks...( points you make for match move )...

           

          This site has a lot of info about greenscreen stuff and I think the HD format info I got about greenscreen ( not camera match move stuff, but greenscreen in general ) I got from using google and typing something like " best format for greenscreen "....

           

          http://www.hollywoodcamerawork.us/greenscreenplates.html

           

          Good luck

           

          Rod

          • 2. Re: Green Screen using AVC-Intra 100 ugly
            Level 4

            A crazy thought...if you're looking at a reshoot...

             

            take a sample and try to convert to sd ( experiment with different fps etc ) before import to premiere and what's not green ( due to 90 degree vertical frame you'll have black space in frame ) key out using color key stuff in premiere ??

             

            Rod

            • 3. Re: Green Screen using AVC-Intra 100 ugly
              Level 4

              Another guess...when shooting greenscreen you want a sharp outline of person and 24fps with movement isnt so great...I think they recommend 60fps but 30fps is probably more common...60 for match move.....anyway, your iso probably changes shooting hd instead of sd ( equivalent to adjusting 180 degree shutter on film camera ? ) and playing back on location would probably look smooth and good but not the same as in editor...

               

              Boy, good luck with this one..

               

              Rod

              • 4. Re: Green Screen using AVC-Intra 100 ugly
                pebalsamo Level 2

                If you haven't already done so you should also check out the Premiere forum on the DVX board.

                 

                http://www.dvxuser.com/V6/forumdisplay.php?f=21

                 

                Phil

                • 5. Re: Green Screen using AVC-Intra 100 ugly
                  Curt Wrigley Level 4

                  HD is actually a much better format to key than SD.  The more pixels at the edge of the matte the better.  And AVC Intra is 4:2:2 color space is better to key than 4:1:1 of DV SD (for example)

                   

                  I assume you have the latest update?  AVC INtra support was recently added with the 4.2 update to Pr.

                   

                  http://tv.adobe.com/watch/davtechtable/premiere-pros-42-update-and-native-p2-avcintra-edit ing/

                  • 6. Re: Green Screen using AVC-Intra 100 ugly
                    mshushan Level 1

                    Morning Curt,  I am in a real pickle:  Just finished the 3rd day of a 4 day

                    shoot capturing 85 of 100 subjects for a corporate piece.  All video on site

                    looked great via sdi out to 24 inch monitor - but here in post its just

                    horrible.  Looks like real noisy DV footage in premiere, final cut, and

                    after effects. Being that this same cameras' 720p has looked great all

                    along, and now my first 1080p 24 is horrid - I either have settings totally

                    wrong or a defective camera.  Please see attached frame for reference. Thank

                    You!

                    • 7. Re: Green Screen using AVC-Intra 100 ugly
                      Level 4

                      Interesting problem...

                      I'm thinking the increased number of pixels in HD if they are blurry during movement of subject isn't "better" than "lesser" number of pixels ( SD ) if due to ISO and fps the SD is sharper... but I don't remember where the references to HD greenscreen shooting is located on web...can't find the articles to share...sorry...

                       

                      Rod

                      • 8. Re: Green Screen using AVC-Intra 100 ugly
                        Curt Wrigley Level 4

                        1080p 24 is a standard preset, so you should be OK.

                         

                        Its disturbing that you have the same problem with FCP; as FCP handles it a completly different way; by creating an intermediate pro res file.

                         

                        I have heard of a case where downloading extra codec packs from the quicktime site has smurfed up Pr.   If you had access to another machine (MAC OR PC) with Pr this would be easy to elliminate.

                         

                        Assuming you are using the correct preset; your footage should look great.

                        • 9. Re: Green Screen using AVC-Intra 100 ugly
                          Level 4

                          Please see attached frame for reference

                           

                          didnt come through...can you try again?

                          Rod

                          • 10. Re: Green Screen using AVC-Intra 100 ugly
                            shooternz Level 6

                            I would be keen to see a screen grab of the raw footage.

                             

                            Also...what Project Preset are you using with what Playback  Preview CODEC?

                             

                            I have been caught a couple of times by the Playback  Preview CODEC.  Note - not all Presets have Preview CODEC options.

                            • 11. Re: Green Screen using AVC-Intra 100 ugly
                              Level 4

                              Poster must be busy shooting more stuff....

                               

                              Found some info on that " hollywood camera " site.....

                               

                              ------------

                              IS HD REALLY HD- GREENSCREEN ISSUES

                               

                              These plates were all shot with an HVX-200, mostly with the 100 MBps DVCPROHD codec. This was good enough for us for Visual Effects For Directors because we had specific needs, but we don't consider them good enough for full film production.

                              Here's why:

                              • COLOR SAMPLING: We      prefer all green screen to be 4:4:4, so every pixel has a unique color.      4:2:2 only updates the color every second pixel, but green screen      desperately depends on a sharp, accurate, scientific color transition.      With 4:2:2, you're operating in half resolution. But if you downsize, like      we downsized to 720x480, you're at full resolution again. So because we're      delivering in SD, the plates are 4:4:4 for us. They'll just be 4:2:2 for      you if you're delivering for an HD movie.
                              • PIXEL ASPECT: When      a camera is listed as 1920x1080 HD, that's really stretching the truth.      You'll see that all our plates are in 1280x1080, which is the original      camera resolution, meaning that the plate has to be stretched 150% on the      X-axis to be in the right aspect. In other words, you're only operating at      66% resolution on the X-axis. Did someone say "smearing"?
                              • NOT EVEN 4:2:2: By      the time 1280 has been stretched to 1920 to make up for the 1.5:1 pixel      aspect ratio, 4:2:2 has been stretched out too, basically becoming      4:1.5:1.5
                              • LENS RESOLUTION: Nobody      besides DPs really thinks about the fact that a lens has a resolution.      Zoom lenses are made of many lens elements in a clever configuration, and      each element introduces some blur. That's why top-notch DPs like to use      prime-lenses cut from diamonds from King Solomon's mines, because if the      lens limits the resolution, it doesn't really matter how well you record      the signal after that. Some people have come to the conclusion that the      HVX-200 is really a 720p camera, because the 1080p resolution doesn't      really come through. We tend to agree, but we don't want to start a      religious war, and will say that it's just our personal experience. On top      of that, we've used a $500 wide-angle adapter on some shots, which really      butchers the pixel resolution, so even though we're recording at 1080p,      we're really not. But 1080p allowed us to record with the 100 MBps      DVCPROHD codec, which meant that we still got a very respectable resized      SD signal out of it.
                              • BAYER PATTERN: Most      cameras use a Bayer pattern on the chip, so that every pixel is EITHER      Red, Green, or Blue — but not at the same time. A full Red-Green-Blue      pixel is derived mathematically by interpolation. It's no wonder that some      organisations are starting to call for an objective standard for what      really constitutes a pixel, because a Bayer pixel is definitely not a real      pixel — more like half a pixel. By the way, there are twice as many Green      pixels than Red or Blue in a Bayer sensor, so you're far better off using      green screen than blue screen on video.
                              • HALO: Even      with the internal sharpness generator completely disabled, the HVX-200 has      a clear black fringe several pixels wide on the right side of actors on      green screen. Panasonic vehemently denies it, but it's very easy to see.      In this      picture, notice that white areas get a fringe, but darker areas, like      her legs or hair, don't. Panasonic's explanation has been that it's just a      shadow from the lighting (huh?), but the halo is on the KEY side — so the      only plausible explanation is a quantum singularity localized to the actor      which bends light as it passes by her body. We think it comes from the      Bayer pattern, but we're not sure. And Panasonic shouldn't feel bad. A Nikon      D80 does it too.
                              • HEAVY COMPRESSION: Even      though it seems like a lot that we're recording at 100 MBps in the      DVCPROHD codec, if you calculate the bit-rate per true output-pixel, we're      actually still compressing at a whopping 15:1.
                              • NOISE: Video      cameras in this price range tend to have rather high noise, and on top of      that, they're usually 8 bits per color channel. This can result in some      highly visible shadow noise that almost pixellates when the brightness is      just on the edge of a bit-threshold. You can see some of our plates doing      this.

                              An HVX-200 and all its brothers and sisters in its price range simply don't have the horsepower for full pixel, high dynamic range, high resolution, uncompressed production that you need to do truly professional green screen. Green screen is ultimately a scientific process, and is one of the most demanding things you can do with your camera. Regular live-action images are MUCH easier for your camera to handle, so for regular filmmaking, your camera is fine, don't feel bad.

                              We have nothing against the HVX-200 or its brothers or sisters — come on, we shot a whole DVD set about visual effects on it — but it's important to really understand what the limitations are. It's fine to own your own camera for regular filming. For green screen, you should consider renting the very best you can afford — and make every decision right, which is where we come in.

                              Thanks for reading!

                               

                              Rod

                              • 12. Re: Green Screen using AVC-Intra 100 ugly
                                Curt Wrigley Level 4

                                You must read this with perspective.   Compared to cameras shooting 4:4:4 color space, HDV or 4:2;2 cams are certainly not as good.  But they are much better than SD DV video.

                                • 13. Re: Green Screen using AVC-Intra 100 ugly
                                  shooternz Level 6

                                  ...and for a real world perspective...I shoot a lot of very successful keys  - shot 720p HVX  (and even posted up some samples in a recent post).   The color space does make a huge difference.

                                   

                                  @the OP.   and FWIW... Last week I shot a character on green screen with the specific intention of keying in a White BG.   It was my preference to do it that way because as a D.P... I feel that I never get the "white" I want from shooting on Digital Cameras.  (Its kind of fake compared to what I can achieve and I am used to , when shooting 35mm film).

                                   

                                  Look forward to seeing your frame grab.

                                  • 14. Re: Green Screen using AVC-Intra 100 ugly
                                    Level 4

                                    pebalsamo, thanks for that link...it's pretty cool...looked through some of the threads..

                                     

                                    Curt, thanks for the clarification on those specs....  at least the poster has some facts to get started looking into his prob, even if those facts are not the whole story...I sorta thought I had heard that  "in some circumstances" HD wasn't great for greenscreen...

                                    Do you know anything about the FPS issue re: blur with movement on screen ?

                                     

                                    Shooternz, thanks for that info....does that mean you shot film recently instead of video?  What camera did you use ? iso, fps, etc

                                     

                                    Rod

                                    • 15. Re: Green Screen using AVC-Intra 100 ugly
                                      shooternz Level 6
                                      Shooternz, thanks for that info....does that mean you shot film recently instead of video?  What camera did you use ? iso, fps, etc

                                       

                                       

                                      Sorry ...I might have been confusing in my post.

                                       

                                      I do still shoot fim (less and tless though) but what I was tring to say that because I had the same requirement as the OP ...character on clean white bg... I shot HD digital and chose to use a key rather than a live white BG.  By key inserting the bg in , I get control of the white "look".    Digital camera white is not the same as  "film white" IMHO.

                                      • 16. Re: Green Screen using AVC-Intra 100 ugly
                                        Level 4

                                        shooternz,

                                        Thanks...I will keep in mind ...if I ever shoot anything...

                                         

                                        Rod

                                        • 17. Re: Green Screen using AVC-Intra 100 ugly
                                          mshushan Level 1

                                          Hey Rod, I need to thank you for all your efforts here. Turns out that I

                                          have some sort of issue within the camera with the Avc Intra codec -- I am

                                          shipping it out to Pani tomorrow. Their tech folks were very responsive and

                                          helpful. We needed to use the camera to finish up this particular shoot --

                                          used 720 without issue, looks great. 

                                           

                                          Thanks, Matt