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Could someone explain what I should be doing here….
I read this tutorial on masking/rotoscoping and I cannot seem to understand what the author wants me to do as far as creating hard frames. Should I just make my video clip lower field first even if it is already set lower field first?
Here is a paragraph from the tutorial.
Before any masking takes place you need to merge your fields together so you have hard progressive frames. This gives the footage a more cinematic look as it creates 30 pieces of information per second as apposed to video
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3 Replies
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Also, should I be creating .tga files from DV in order to make great masks of sports players or is just masking them in DV just as good?
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Each frame of interlaced video footage contains two different images taken in different moments. The reason for this comes from an old necessity for solving tv flicker. That’s why, when you see footage you may find that there are kind of horizontal lines where objects move, because even and odd lines belong to the first or second halfframe (field). Depending on the system, NTSC, PAL, etc, the odd lines may be before or after the even lines, that’s why you must sometimes tell the program whick the first field is, the “lower” or “upper”, or your exported move will flick annoyingly, regardless of having effects on it or not.
Additionally, you can choose “deinterlace fields”, also called “motion detect”. That will merge the two fields so that they will contain just one image each frame. Data of still objects merge and data of moving objects are vertically blured by one pixel. (there are more complex ways to do that). What interests you right now is the fact that if you rotoscope an object that has two different positions in the two fields, the mask won’t cut the object properly, as there will be only as much as a single mask for each two different fields. So the best choice for you probably is to choose that deinterlace option in the “interpret footage” window. That way, what you see when you put the mask there is what you get when you export.
There could be talked much more about this, but I think that will probably be enough for what you need to do.
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“Lower field dominant” is probably the wrong term, though this usage is common. It should be “lower field first”. In other words:
Your video card chooses to place the field that occurs first in time below the field that occurs second in time. The first field would then be lines 2,4,6, etc. while the second field would be lines 1,3,5, etc. Hence, “lower field first”.
To paraprhrase thehardmenpath, you should choose “separate fields” in the interpretation box, and choose “lower field first”, since that is how your video card created the fields. You are now telling AE to separate fields so you can do the next step: Create a comp at the same size and pixel aspect ratio as your clip, but with double the frame rate. For NTSC this would be 59.94 fps, for PAL it would be 50 fps.
You need to do this if you expect to render to fields (at the regular frame rate) at the end of it all. If you don’t, then the mask will move a little strangely, because it will only be drawn on every frame, not every field. Do you see?
However, if you expect to exercise your aesthetic choice to render to frames (not fields), then masking in your regular frame rate (29.97 or 25) is quite fine.
And yes, masking in DV is fine. The degradation happened when the original DV file was created, so rendering to TGA before masking won’t make it better. 🙂
Hope that helps,
Steve
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