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Corner pin and basic matte question

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Oliver PoolCorner pin and basic matte question
by on May 31, 2011 at 12:46:53 pm

Hi guys. If you have any pearls of wisdom to help a noob I'd be really grateful!

I am working on a video clip of a man holding a board. I want to project an animation onto that board as it moves around the screen. Obviously I need to corner pin using motion tracking, but there's more to it than that as the man's fingers are on top of the board, so I need to make sure that they are still visible too.

What is the best way to go about doing this?

So far I have used Rotobrush to select the visible area of board (i.e. the bit that isn't covered by the fingers), but although I have managed to isolate the board I can't then make that go transparent to allow my animation layer below it to show through. I had thought about using a mask but because of the fine detail on the fingers I assume that a mask wouldn't allow some of the background colour to show through around the fingers.

I'm sure the answer is something to do with matteing but I can't figure out the right way to do it.

I'm fairly new to this so please feel free to patronise!

ps I am using After Effects CS5.5.

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Cassius MarquesRe: Corner pin and basic matte question
by on May 31, 2011 at 2:05:51 pm

What color is the board? can you isolate either by color ou luminance? So it will become a matter of simple masking.

Post a screenshot, it will help.

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Oliver PoolRe: Corner pin and basic matte question
by on May 31, 2011 at 9:15:36 pm

Thanks Cassius. Dave yes, this is just a test, don't worry!

Here are screenshots, can you point to what I need to do? First screen shot is of the footage,

second one is of the matte I have made.

There's another layer which is the image I want to project onto the folder, which isn't visible in either.

As the board is coloured blue, I guess from what you say Cassius that it should be simple to mask it - but how to go about doing that seems to be too basic for all the tutorials I've looked at! Many apologies to make you go through such basic stuff, but it is massively appreciated.

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Cassius MarquesRe: Corner pin and basic matte question
by on May 31, 2011 at 9:35:36 pm

what I was trying to say is, use everything you have there to track the footage, either within after, or using mocha.

Then as the folder is blue I would use keylight (effects panel) to mask out the blue. just put this layer ontop of everything and this should put back your fingers without the need to rotoscope anything.

The "simple masking" I was referring was that if you had anything else blue going on, maybe you would need some loose masks on those to make it work. (e.g blue glasses and he had lifted the plate for a few frames)

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Dave LaRondeRe: Corner pin and basic matte question
by on May 31, 2011 at 4:06:30 pm

You may also want to look at Mocha, a really good motion tracker that comes bundled with AE. You'll want to run the Imagineer Systems tutorials appropriate for your Mocha version.

It's a good thing you left an area for the talent's hands. It will save you a lot of work, and I sincerely hope this is for a test and not for your final product.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

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Roland R. KahlenbergRe: Corner pin and basic matte question
by on Jun 1, 2011 at 2:14:18 am

Don't forget your markers on the board. I've seen lots of tutorials where markers are given a miss and the obvious result is slippage with the insert image. The slippage is obvious but for some reason even the tutorialist (word?) seem to be oblivious to the issue.

Mocha likes textures - so, use cut outs from old magazines as markers. Looks for images that aren't too busy. Those that provide obvious seperation without being too busy are good bets. I find ads in magazines generally provide the best option as there is usually some white or colored space within the add that surrounds a product.

Do no place the markers too close to the edge. Even with reflective surfaces, if the object to be tracked doesn't naturally provide for markers, placing your own markers are always a good way to ensure a more solid track.

Masking the fingers is always relatively easy - just ensure that the fingers do not more about during the shoot - just to make your post-job easier.


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Danny HaysRe: Corner pin and basic matte question
by on Jun 2, 2011 at 3:39:34 am

Too bad the board isn't green or blue. You could key out the green or blue and let the underlying video show through. Then you would only need to motion track it to keep it in the same place on the card.

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Oliver PoolRe: Corner pin and basic matte question
by on Jun 4, 2011 at 8:51:56 am

Thank you all so much for your help.

You've helped me discover Mocha - its motion tracking is awesome isn't it!

Can I ask one more question about masking the hands. Roland thanks for your help - you say masking the fingers is easy but I'm not quite sure how to do it. Just using keylight 1.2 to make the folder transparent hasn't been that great - should I be using a mask instead? If so, is auto-trace the way to go or is there some other technique that I'm missing?

Thanks again for the help, all. Much appreciated

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Michael SzalapskiRe: Corner pin and basic matte question
by on Jun 21, 2011 at 7:44:04 pm

I wouldn't use Auto Trace at all. You should either rotoscope using traditional methods or try the new Roto Brush. Resources for both things are here [link].

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(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

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Oliver PoolRe: Corner pin and basic matte question
by on Jun 24, 2011 at 5:36:25 pm

Thanks to all of your for your help. I've manged it - my test is here:

I've written out a more step by step guide for any other newbies who find this - clearly it'll be stating the obvious for any Creative Cow regular though:

1.Bring footage into composition, ensuring composition has same values as the footage (frame rate etc).
2.Make a duplicate of the footage in AE. This will be the backgrond. Call the top one “mask” or something.
3.Bring the animation into the composition, in between the two layers.
4.Motion track the folder using Mocha: Open Mocha. Open Project and it asks you to import some footage. At this point, make sure that the footage you work on and the composition in After Effects are the same, and have the same fps etc. First put a garbage matte thingy wide around the folder (to finish the matte, right click). Then click on “Surface” and it gives you 4 points – bring them to the corners of the folder. Then scroll back and forward through the timeline to check they are in the right places. If not, you can move them. Once that's ready, select “Export” and "copy to clipboard".
6.Back in After Effects, select the animation layer (making sure you're at the start of the clip) and press paste – that should paste the motion track onto the animation and the animation should now sit on top of the folder – if it doesn't, then reposition the anchor of the animation's layer until it does.
7.Now make the folder on the top layer see through. Use the “Linear colour key” effect to select the colour of the folder and make it disappear (or “key it out”), then use keylight 1.2 to tidy it up.
8.If there is some interference elsewhere in the picture use a wide mask around that and keyframe it so it follows the folder.
9. Add to render queue, and then down the bottom click output mode. H264 is best format for youtube apparently.

There we are.

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