Announcement

Collapse
No announcement yet.

Green screen advice BMPCC, exposure, WB, gray card

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Green screen advice BMPCC, exposure, WB, gray card

    Hello,

    I've seen a few threads here on green screen but was wondering if anyone had some general tips on shooting green screen with this camera. It's the 1080p sensor so no extra resolution to work with but I'd like to get things exposed properly at least.

    The main issue I have with this camera so far is shooting film profile, WB, and exposing correctly. I don't have scopes on my field monitor, what I've been doing is ETTR, set zebras at 95% and stop down to just below them. It seems to work out ok sometimes, and other times not, can't seem to narrow down what I'm doing wrong when it doesn't work.... As far as WB, the preset temps leave a lot to be desired so I usually have to adjust in post if it's shot indoors or has any mixed color temps.

    I've tried my best to tweak my AC7 monitor to match to the camera's display "video" profile (recording film, displaying video in BMPCC) but I can never really get a perfect match, it's close.

    If I were to expose based on what I'm seeing in the monitor, (a film (log) ProRes HQ HDMI output adjusted to match video "look,") is this the wrong way to go about it? Can anyone recommend how to effectively use an 18% gray card in this situation? Thanks!

  • #2
    Sell the smallHD and buy a proper monitor that has scopes r at least rent one. I own the ikan d5w and there's no way in the world I would shoot without scopes on this camera, there's a reason scopes exist in the first place....

    Secondly people have shot on Green Screen with SD cameras, then 720p and 1080p. The Pocket camera has a better compressed codec than almost any video camera before it, being beat by only the top cinema cameras. If you need something with more resolution than rent a RED, if there's no budget then make it happen with what you have.

    Here's an excellent monitor buy smallHD that you could at least rent for the weekend and produce your project
    http://www.lensrentals.com/rent/vide...led-sx-monitor

    Ultimately what you want to do is just light evenly, I would suggest you use a light meter and you will not have any problems. Shooting Green Screen in a control environment is actually very easy, we have all of these tools available for us......

    Comment


    • #3
      First, you do not have to sell your monitor
      As mentioned the most importatnt thing is to have the greenscreen lit evenly (and without mixed color temperature lights). If you have a smartphone, there's a great little apps to help you with this:

      Android
      https://play.google.com/store/apps/d....greenscreener

      Apple
      https://itunes.apple.com/ca/app/gree...604935529?mt=8

      WB according to your light source but you'll have enough room to be off the 'right' WB. If your monitor is close to the camera's screen, if the green looks green to you you'll be fine. When raw is there for the Pocket it'll get even easier.

      Comment


      • #4
        Originally posted by stip View Post
        First, you do not have to sell your monitor
        As mentioned the most importatnt thing is to have the greenscreen lit evenly (and without mixed color temperature lights). If you have a smartphone, there's a great little apps to help you with this:

        Android
        https://play.google.com/store/apps/d....greenscreener

        Apple
        https://itunes.apple.com/ca/app/gree...604935529?mt=8

        WB according to your light source but you'll have enough room to be off the 'right' WB. If your monitor is close to the camera's screen, if the green looks green to you you'll be fine. When raw is there for the Pocket it'll get even easier.
        Cool little app there man.

        Comment


        • #5
          Green Screener looks great. Thanks

          Comment


          • #6
            Thanks a lot for the tips, and the app looks really helpful I will definitely try that next time.

            Even with chroma pumped all the way up on the monitor, the green screen doesn't really ever get "green" like it would without the film profile, stays pretty gray. While I objectively know the color is in there, it's a little bit unnerving. So in the end just worked for decent even lighting, without knowing the IRE or color... Came out ok, but I'd definitely feel more comfortable if I could at least see a preview of something closer to final on set.

            Comment


            • #7
              Y'know, for the best keys, you really have to test with what you have or will be using - camera, codec, lights, and software.

              In Keylight, if you open a new window of your footage (with render set to "off") and set Keylight to "status", you can hold down option and move the cursor all around the green until "status" shows the most black. While this is a great way to find the "best" green, two things become immediately apparent: even in a well-lit screen, there's a lot of variance (maybe at the pixel level), and... keylight "prefers" some greens over others.

              So finding the best green exposure for your camera in a given WB situation with a given keyer is pretty critical... testing is the best way to get there. Problem is, doing this without a waveform monitor or exposure level indication makes it hard to repeat. "F 5.6 at 1/60th" can be all sorts of things... knowing the exposure level is really helpful.

              That said, I just pulled a test key with a Nikon D7100 that kinda blew my mind for a DSLR (that camera's pretty amazing)... but the best thing you can do is shoot a big frame - 2.5k, 4k, etc.

              Comment


              • #8
                I recently did a bunch of blue screen shots using the false color feature on the DP4, grey card, and light meter. I'm just starting to work on them but so far they look good. The person being keyed had a Halloween costume that had that mesh see through material and even that is looking pretty good. Here's how I setup them up. Don't know if it is the correct way but it worked for me, so maybe it will be helpful for someone else. The usual tips apply, even lit screen, distance between your subject and screen, some back light to help with spill, not wearing clothing the same color as your screen... My lenses are Nikon so I have to use a Nikon G to EF adapter, which means I don't have any f stop markers for exposure. I use the false color view on the DP4 to set exposure. From previous testing with my camera setup, lenses, and a grey card / color chart I know that my light meter reading or skin tone area is when the grey card turns orange. For setup I will use a light meter and then set / check exposure with the false color.

                I had a 10 x 14 or so blue screen. I lit it with two fluorescent soft boxes from the sides close to the screen. I also had one 2x4 fluorescent panel maybe 6 feet or so further down from the blue screen on one side to help even out the center of the screen. Checking with the spot meter function on my light meter I was getting a consistent f4 across the screen. For the person in front of the screen I used two tungsten 650 Fresnels and a tungsten 300 for a back light. I tried to keep the front lights from spilling too much on the blue screen. I didn't have anything to control the fluorescent soft boxes so the person was also getting some light from them. I tried to get the subject lit a little hotter than the blue screen so set them to f2.8. Then I double check the blue screen with the spot meter to make sure it is still consistent. When viewing the scene with just the blue screen and grey card on the DP4, the screen was a solid purple and the card was a solid orange. For WB I set the camera to 3200 for the tungsten. The fluorescent lights are daylight balanced, but since I was using a blue screen I let them go uncorrected. Then I bring in the person. I did any exposure adjustments on the camera to make her skin orange in the DP4, double check the scene, see if any zebras or yellow areas are showing up, and then start shooting.

                I was shooting in raw film mode, (BMCC) so I don't worry about how it looks in the camera LCD screen or the DP4 color wise. I know if my exposure is good and WB is close it will be good. Now if someone could give me some tips for keying / masking blurred hair that would be very helpful right now!
                Tim Veal
                http://sandstoneproductions.net
                My blog

                Comment


                • #9
                  Originally posted by vealti View Post
                  Now if someone could give me some tips for keying / masking blurred hair that would be very helpful right now!
                  That kind of thing should be doable with a good keyer, if you tweak the settings in the right way. It's possible you might have to apply different settings to different parts of the keyed image to get it right.

                  No idea if you're in FCP X, but this might help (discussing how spill suppression can help with hair edges):

                  http://www.macprovideo.com/hub/final...n-better-keyer

                  …and then follow it up with this (discussing how to recover foreground elements with an extra duplicate of the original clip):

                  http://www.macprovideo.com/hub/final...er-keyer-again
                  Iain Anderson, Apple Certified Trainer
                  http://trainingbrisbane.com

                  Comment


                  • #10
                    IMHO, having a waveform monitor makes lighting the screen fairly straight forward. If you have a thin even line across the monitor you're good to go. Line thickness is important as it indicates top to bottom evenness. A fat line means uneven light vertically so what keys well at the top of the picture won't key as well at the bottom. You want a thin line. While you can do it with a meter, the WF monitor makes it go much quicker.Checkout this iPhone app http://www.adamwilt.com/cinemeter/

                    Comment


                    • #11
                      It's possible to do GS / BS shoots with just a meter, but either a scope or false color make a huge difference. Using a still camera to set the exposure on a cinema cam seems like a crazy workaround. I can't imagine any clients seeing that without becoming panicked about good exposure. At a minimum, a light meter seems like a safer, more professional way to go. Personally, I have a DP7 with false color and a 17" with waveform running on most of my keying shoots. The scope just works great, but the false color is excellent at identifying exactly where luminance variance is occurring on the screen.

                      When I read above that people are doing GS by finding 100 on the zebras and backing off, red flags begin to go off. Good keying depends on good saturation, and saturation goes down as luminance goes up. For most small-medium spaces, green screen should be roughly 1 stop below key and blue screen at least another .5-1 stop down. My first blue screen shoot with the BMCC raw bore this out exactly. The screen was 1.5 stops down from key but I still had to lower the raw exposure a bit to get the key to pop with one click across multiple clips.

                      Good luck!

                      H

                      Comment


                      • #12
                        Mark Christensen's After Effects books have the best breakdowns of keying difficult shots I've ever seen. The CS5 book added some great tips for picking your green, so if a more recent version isn't out yet, his CS5 book is worth every penny. Keep in mind you may need to split a hard key into several pieces/layers and key things independently, use some animated masks, etc.

                        They're also great books, very readable and kinda fun if you're geeky about AE. Got mine on Amazon.

                        Comment

                        Working...
                        X