Creating clean plates to use for difference matte

i’m working on a rather huge rotoscoping project, so naturally i’m looking for ways to ease the pain…
i’ve stumbled across that youtube video “lobster remove” demonstrating mokey’s powers…
would i be geting acceptable results using the lobster free video in a difference matte with the original video, to get just the moving lobster? or is this just crazy talk?
i’m using mocha ae right now but i’d switch to pro, if clean plates could be used that way for difference mattes

well it’s good to know that useing a composed clean plate for a difference matte isn’t impossible … guess that’s what i actually wanted to know …
i’ve watched a few youtube videos showing difference mattes, so i’ll prepare to deal with creating garbage masks to get the result i want…
as for the project … i’ve to get rid of the whole background, so the roto work has got to be as accurate as possible…
spending my time learing about rotowork i’m under the impression that hard (sometimes frame by frame) work gets you the best results…
thanks for you reply …

i totally agree… frame by frame is last resort … i’ m used to track noses and jaws by now :slight_smile:
i don’t quite understand what knots are supposed to be … is it bezier splines you are referring to?
for hair in close up shots i’ll use a still image masking program called fluid mask… gonna be painful :slight_smile:
by the way is there any reason i should switch from mocha ae to moch pro (besides mokey for the clean plate idea)?

You can get a difference matte this way, but keep in mind you will run into the same issues with any difference matte, such as grain, lighting and colour shifts.
For example, if you removed a surfer standing on a beach and their skin tones matched that of the sand, you would probably run into problems.
It will definitely get you most of the way for some shots, but you won’t always get a clean difference.
You can try out Pro on trial mode, so you can always give it a shot to see if it works for you.

—Quote (Originally by JuergenProksch)—
spending my time learing about rotowork i’m under the impression that hard (sometimes frame by frame) work gets you the best results…
—End Quote—
That’s why we developed mocha: To make the hard work easier! But you’re right, sometimes frame by frame is unavoidable. You take each shot as it comes. :slight_smile:

Well, it depends on your needs. We have the lens, insert, and remove tool in mocha pro, and you can see a breakdown here of what each version has that the others do not: Boris FX | Mocha Pro 2022.5
The lens tool looks at straight lines in a shot and tries to build a camera warp off of that for straightening out a shot or adding elements backin with warp.
The insert tool is a handy tool that makes screen replacement work faster and easier, with previews and A over B rendering with motion blur right in mocha pro.
The remove tool is self explanatory, it removes objects and wires, et all, from scenes as long as you have a clean-plate, can make one, or can at some point see behind the object.
Hope that helps!

Keying a process. even with the best green screens, you almost always need to combine different keys.
Difference keying rarely works in any usable way. some times, if you’re lucky, you can get an arm or face or some hair detail.
It also depends on what is going behind the roto’d foreground. if you’re adding a few things to the background here and there, you don’t need much of a matte, but if you’re replacing the bg completely, then its a lot more work.
Helps if you are doing the final composite, too. If you can make adjustments and color corrections you can hide harsh edges and feather things together.

well, frame by frame is a last resort. Selective tracking is always best.
I use mocha almost entirely for the tracker. forearms, shoulders, chest, thighs, side of the face, top of the head, ear… breaking down the talent into a skeletal hierarchy will always give you the best results.
A full replacement should give you some room for skipping some detail. it’s an art. just add a couple wrinkle details on the arm or waist.
Start with frames that have fewer details and add knots as you go and only when Absolutely necessary. Mocha does a great job of maintaining the shape of the curve.
If you’re not exporting to another compositing app, you can even turn off knots.
finally, the hair. Exhaust ever possible keying method first: color, luma, inverted luma, diff.
If you’re still not there, you can track hair patches back onto the head. That’s a whole different process completely.