3 Replies Latest reply on Apr 12, 2012 1:26 PM by Fevmac

    Roto Brush - Refining the Matte




      I’ve been having a problem trying to finish a Project I’ve made using the roto brush tool. I’ve created the segmentation using the roto brush tool, I’ve froze it and then I´ve used the regular brush tool to touch it up.


      So far all went ok, I’ve put a good amount of hours in making the effect, and to finish I just needed to Reffine the matte using “Effect controls tab”, and that’s whem things went bad.


      As soon as I’ve selected the “Refine Matte” box I’ve lost the segmentation on some frames. The segmentation was not lost completely, whem I look on the alpha chanel for example, instead of having the “black and white” contrast between the person I’ve selected and the background, all the background turns to gray.


      Whem I see previews of the clip in the timeline, those frames where the background turned to gray get some kind of weird blur with the colors of the person’s clothes.


      Here are some screenshots comparing the good and bad frames.



      Good frame


      Alpha Good.jpg


      Bad frame


      Alpha Bad.jpg



      Good frame


      Preview Good.jpg


      Bad frame


      Preview Bad.jpg


      It’s possible to see in the images that the touch ups I’ve made with the regular brush tool are there. I’ve also tested and I can erase the “gray/blur” areas using the regular brush, but that way I’ll have to go thru the video frame by frame again, and I’m hoping there’s a better way to do this.

      I really need this help, and I appreciate any tip that can help me with this.


      Thanks for the time and good will!

        • 1. Re: Roto Brush - Refining the Matte
          Mylenium Most Valuable Participant

          Nothing wrong, I'd say. The Alpha was never clean in the first place and refining the matet simply responds to some artifact that you may not see, but technically are already there like tiny fractions of non-transparent pixels with just 0.1% opacity or something. You could try and render the raw clip out to a format which supports Alpha. The forced quantization might eradicate the offending pixel garbage and you can then apply any refinements to the re-imported clip. The same could be done by pre-composing teh Rotobrush result. and naturally, you might consider adding some garbage mattes/ masks somewhere in there to prevent stray pixels influencing your result. It's realyl just a workflow problem...



          • 2. Re: Roto Brush - Refining the Matte
            Fevmac Level 1

            first I want to thank you for the fast, and very helpfull reply!


            I've exported to FLV and imported the clip again and seens to work fine at first, but I would have to re aply roto brush to use the refine matte, and the pixel are still there even with compression. (With the compression they are visible)


            Whem you say to pre-compose the rotobrush result you mean theres a way I can erase those pixels before applying refine matte? Becose the workflow problem is non-visible until I use the effect.


            I used a black solid mask on the roto brushed person on my clip, but now instead of blurring the clothes colors the mask is blurred.


            thanks again for the help, if you can give me this final orientation I would be even more grateful!

            • 3. Re: Roto Brush - Refining the Matte
              Fevmac Level 1

              I did some extra research and it turns out I can use the "refine matte" without having to apply the roto brush, so thats problem solved for me


              Thanks again for the help! I really apreciatte it!