motion difference matte? at DVinfo.net

Nathan Quattrini · August 19th, 2007, 07:42 AM

I seem to remember some years ago learning about a matte that takes 2 video files and compares the motion in them, creating a matte from the pixels that are different (moving). Is there such a thing? Or is my memory making things up that I wish were possible?

Giroud Francois · August 19th, 2007, 07:59 AM

it is not possible since even between 2 frames, the same pixel will likely not give the same value.
Despite this fact , there are some programs that are able to track an object with or without reference background.
for a rough mask, this can work nicely, but the quality of a mask is in the borders, so from that point of view, it is most of time very difficult to obtain good results.
i nice program to use is MOKEY
http://www.mokey.com/products/mokey/

Jiri Fiala · August 19th, 2007, 04:34 PM

It is possible, and it's called Difference Matte. With some tweaking of the color space, denoising and blurring the clean plate and so on you can pull a somewhat usable mask. I did this in Fusion when I needed to key out a dancing person from a garage for additional color correction. Your shot has to be really static, with same lighting conditions and noise-free. Even then I had to make an animated garbage matte around the moving person, because the key wasn't too clean.

Try to avoid this technique.

Ben Winter · August 19th, 2007, 08:04 PM

I've never gotten the difference matte to work. Ever.

Nathan Quattrini · August 19th, 2007, 08:07 PM

intresting. Well i filmed it today to try so we`ll see what happens later when i get to editing. :D Any tips are helpful

Jiri Fiala · August 20th, 2007, 03:17 AM

What do you use as FX app? I did this only in Fusion, but Diff Matte exists even in Premiere (but I cannot imagine ever getting anything usable from it without extensive cleaning).

Nathan Quattrini · August 20th, 2007, 09:24 AM

I`ll e editing on CS3 eventually, premiere and after effects

Andrew J Morin · August 20th, 2007, 02:03 PM

I just recently learned how to use the "matte choker" effect in AE. Use with (any of ?) the keying effects; adjust those keys so that the maximum amount of your background keys-out, what usually happens is at some point parts of the foreground start to fade too. The choker then goes in and magically locates those little transparent islands and gets rid of them. Does a nice job on edge blending as well.

At least on my miniDV-painfully-cheap-green-screen footage...

andy

Glenn Chan · August 20th, 2007, 02:14 PM

Quote:

I've never gotten the difference matte to work. Ever.

I've gotten it to work for me... shot HD resolution to an Avid (DNxHD codec/compression), downres to SD and deinterlaced by discarding a field.

The camera was a full-sized Panasonic HD camera... HDC-900 I think (it is not a very common camera; it is not the HDX900).

August 19th, 2007, 07:42 AM	#1
Nathan Quattrini Major Player Join Date: Jan 2007 Location: Warwick, Rhode Island Posts: 740	motion difference matte? I seem to remember some years ago learning about a matte that takes 2 video files and compares the motion in them, creating a matte from the pixels that are different (moving). Is there such a thing? Or is my memory making things up that I wish were possible? __________________ Cinematography Site

August 19th, 2007, 08:04 PM	#4
Ben Winter Trustee Join Date: Jun 2005 Location: Hollywood, CA Posts: 1,675 Images: 1	I've never gotten the difference matte to work. Ever. __________________ BenWinter.com

August 19th, 2007, 08:07 PM	#5
Nathan Quattrini Major Player Join Date: Jan 2007 Location: Warwick, Rhode Island Posts: 740	intresting. Well i filmed it today to try so we`ll see what happens later when i get to editing. :D Any tips are helpful __________________ Cinematography Site

August 20th, 2007, 09:24 AM	#7
Nathan Quattrini Major Player Join Date: Jan 2007 Location: Warwick, Rhode Island Posts: 740	I`ll e editing on CS3 eventually, premiere and after effects __________________ Cinematography Site

August 19th, 2007, 07:59 AM	#2
Giroud Francois Inner Circle Join Date: Feb 2004 Location: switzerland Posts: 2,133	it is not possible since even between 2 frames, the same pixel will likely not give the same value. Despite this fact , there are some programs that are able to track an object with or without reference background. for a rough mask, this can work nicely, but the quality of a mask is in the borders, so from that point of view, it is most of time very difficult to obtain good results. i nice program to use is MOKEY http://www.mokey.com/products/mokey/

August 19th, 2007, 04:34 PM	#3
Jiri Fiala Major Player Join Date: Feb 2007 Location: Brno Czech Republic Posts: 453	It is possible, and it's called Difference Matte. With some tweaking of the color space, denoising and blurring the clean plate and so on you can pull a somewhat usable mask. I did this in Fusion when I needed to key out a dancing person from a garage for additional color correction. Your shot has to be really static, with same lighting conditions and noise-free. Even then I had to make an animated garbage matte around the moving person, because the key wasn't too clean. Try to avoid this technique.

August 20th, 2007, 03:17 AM	#6
Jiri Fiala Major Player Join Date: Feb 2007 Location: Brno Czech Republic Posts: 453	What do you use as FX app? I did this only in Fusion, but Diff Matte exists even in Premiere (but I cannot imagine ever getting anything usable from it without extensive cleaning).

August 20th, 2007, 02:03 PM	#8
Andrew J Morin Regular Crew Join Date: Dec 2005 Location: Chicago, IL Posts: 140	I just recently learned how to use the "matte choker" effect in AE. Use with (any of ?) the keying effects; adjust those keys so that the maximum amount of your background keys-out, what usually happens is at some point parts of the foreground start to fade too. The choker then goes in and magically locates those little transparent islands and gets rid of them. Does a nice job on edge blending as well. At least on my miniDV-painfully-cheap-green-screen footage... andy