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andrewmsmith
andrewmsmith
Participant
September 27, 2018
Answered

Using Roto Brush for two separate objects in the same clip

  • September 27, 2018
  • 2 replies
  • 4206 views

I have a clip with two people in it and I'd like to Roto Brush each of them separately.  Since Roto Brush works in the layer panel that seems to limit it to one object per file.  I tried adding the second person after completing the work on the first person, however, Roto Brush wanted to connect them / add the background to the selection after a few foreground selections.  Adding a second copy of the Roto Brush effect to the footage in the layer panel seemed to confuse the system and affect the work that had already been done for the first person.

Obviously, if this were just an effect on a footage layer it would be easy to duplicate the layer, but the paint tool workflow that Roto Brush uses appears to make this task difficult.  Does anyone have any suggestions for how to do this without making a second copy of the source footage and importing it separately?

Andrew

    Correct answer Rick Gerard

    Rotobrush is finicky, doesn't like low contrast edges, requires a lot of patience, and some shots are just more trouble and take more time than doing the roto by hand. That said, there is nothing keeping you from propagating two separate masks in the same shot. When they cross each other they can be divided again, it just takes time and careful adjustments. If you want to use two copies of the footage and cut each out separately it will probably take you a little bit longer, but there's nothing that says you can't do that. The only problem with that is that Rotobrush is resource intensive and unless the shot is just under 10 seconds long, you should freeze the roto as soon as it is finished then render a digital intermediate using a suitable production format of the footage with an alpha channel. At the very least you should pre-compose any layer that you plan to Rotobrush, open the pre-comp and run Rotobrush on the footage. You should not have other layers with effects applied in a comp that is using rotobrush and it's extremely important that you freeze the roto as soon as it's done.

    Show us the shot and maybe we can suggest a little simpler workflow but the way you are describing it all you can do is make sure you are only processing frames you will use in the final edit and follow the recommended workflow in the Help files.

    2 replies

    Mylenium
    Mylenium
    Legend
    September 27, 2018

    Well, as Rick said, it's likely you are simply using the wrong tool. some tracking and masks may be much better, but without seeing the footage, nobody can tell you exactly what you would need to do.

    Mylenium

    R
    Community Expert
    Rick GerardCommunity ExpertCorrect answer
    Community Expert
    September 27, 2018

    Rotobrush is finicky, doesn't like low contrast edges, requires a lot of patience, and some shots are just more trouble and take more time than doing the roto by hand. That said, there is nothing keeping you from propagating two separate masks in the same shot. When they cross each other they can be divided again, it just takes time and careful adjustments. If you want to use two copies of the footage and cut each out separately it will probably take you a little bit longer, but there's nothing that says you can't do that. The only problem with that is that Rotobrush is resource intensive and unless the shot is just under 10 seconds long, you should freeze the roto as soon as it is finished then render a digital intermediate using a suitable production format of the footage with an alpha channel. At the very least you should pre-compose any layer that you plan to Rotobrush, open the pre-comp and run Rotobrush on the footage. You should not have other layers with effects applied in a comp that is using rotobrush and it's extremely important that you freeze the roto as soon as it's done.

    Show us the shot and maybe we can suggest a little simpler workflow but the way you are describing it all you can do is make sure you are only processing frames you will use in the final edit and follow the recommended workflow in the Help files.

    andrewmsmith
    andrewmsmithAuthor
    Participant
    September 27, 2018

    Thank you Rick and Mylenium for the quick and helpful responses.  Sometimes you just need someone who's more familiar with a tool to confirm its features and limitations.

    Andrew

    PS - The shot is of two martial artists in a dojo so their white clothing and the light colored mat and wall color are the low contrast challenge.  Lots of motion blur too.

    Roland Kahlenberg
    Roland Kahlenberg
    Legend
    September 27, 2018

    Use two source copies; one for each subject you want to roto. It's much easier if you work with the tools as they were designed.

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