Mattes Overview

Because Previzion is capable of calculating the position information of the cine camera, it is also able to track mattes in real time.  This allows for a very powerful real time composite that has production quality finish.

Mattes in Previzion can be entered as 3D surveyed points and drawn mattes.  These can then be sorted, named, selected to be active or not, and assigned as “Garbage,” “Keep,” “Foreground” and “Despill.”

To activate all mattes, simply click “ENABLE” or use the hotkey “M” on your keyboard to toggle the “ENABLE” button.

To see the outlines of the mattes, click “SHOW” or press “N” on your keyboard to toggle “SHOW.”

Sorting Mattes

When dealing with multiple mattes in your Holdout Mattes list, you may use them in any combination as either a drawn or surveyed matte and sorted to achieve the desired effect.

To sort mattes, simply highlight the matte you need to move and, using either your up/down arrow keys or the up/down arrow buttons next to the Holdout Mattes list, move them to whichever order necessary.

Mattes are “seen” from bottom to top.

Toggle On/Off Individual Mattes

When dealing with multiple mattes, there may be cases where you may not use a matte or another.  Instead of removing an matte and then having to re-add it later, you can simply toggle it off.

To Toggle Individual Mattes On/Off, simple select the matte by highlighting it on the Holdout Mattes list.  At the bottom of the list, there is a checkbox to the left of “Name.”  If that box has an “X” in it, that matte is on.  If it is empty, it is off.

Naming Mattes

To help keep track of mattes, you may name then or rename them by selecting the matte from the Holdout Mattes list and changing the name in the “Name” input box at the bottom of the Mattes list.

Blur Matte Edges

In addition, Mattes can the have their edges blurred to create a more seamless result.

Values can either be entered by typing a number in or using the drag-slide and clicking and dragging up/down to the desired value.

A good non-intrusive ballpark figure for Blur Radius is 20-30 pixels.

Survey Mattes

Surveyed Mattes where each vertex has an X, Y and Z coordinate that is measured within the Intersense Constellation coordinates.  This allows for very powerful mattes that track precisely to real world objects that either need to be removed or kept in the composite.

Multiple mattes are most effective as surveyed mattes.  Typically, each corner of the green screen walls and floor are surveyed and made into their own matte.

We recommend surveying the green screen walls’ corners at the same time the fiducial markers are being surveyed so they are both on the same coordinate system.

Surveyed Mattes are limited to four vertices and, hence, quadrilateral shapes, like squares and rectangles.

Read the Survey Mattes Section to learn more about creating and editing Surved Mattes.

Drawn Mattes

Drawn Mattes is very quick and efficient tool that allows for areas and shapes to be quickly.  These can then be set to a known distance from the camera and, for most angles, creating a realistic matte that tracks with the composite.  Drawn mattes can have as many vertices as necessary or extend beyond the viewing area of the screen.

The limitation of survey mattes is that the can only be created as flat surfaces parallel to the camera sensor plane.

Read the Drawn Mattes Section to learn more about creating and editing Drawn Mattes.


Matte Types

Depending on the application, you may need to add a matte to remove keying from an area or adding a set piece back to the composite.  With that in mind, Lightcraft has implemented 4 types of mattes to handle most all applications:

  • Keep Matte
  • Garbage Matte
  • Despill Matte
  • Foreground Matte


Keep Mattes

This is the most commonly used matte on green/blue screen stages.  Keep Mattes are able to show what is inside its boundaries and discarding all that is outside of it.

Keep Mattes is the proper type to set your green screen walls as this is what allows for shots that start or end in a framing that goes beyond what the green screen covers.

That way, if the edge of the green screen is captured in the framing, it is not seen and it blends seamlessly with the areas that are covered by the green screen.

Garbage Mattes

Garbage Mattes are able to remove whatever is inside its boundries and show all that is outside them.

An application of this would be to remove an elements that is coming through the camera video that should not be in the shot, like a light, for instance.  You may draw a matte  around the given light and then set to that matte to “Garbage.”

That way, you can remove unwanted set elements from the shot without having to frame them out.  This works best when the element does not intersect or interact with set elements and people.

Despill Mattes

Despill Mattes overwrite the key making everything inside its boundaries solid, with no alpha and removes the given key color.  Anything inside a Despill Matte that is the color of your keyer is turned gray.

A good example of an application for Despill Mattes is setups that involve shooting out windows and doors on a real set where outside, is all green screen.  If the green screen yields too much green reflections on set elements like a shiny floor, normally everything that is green will be keyed and, thus, see-through with an alpha.  For these instances, you may draw a matte around the area that should not have any alpha and use it as a Despill Matte.

Foreground Matte

Foreground Mattes bypass all keyer, color correcting and despill setting and pass-through the original camera signal to everything that is within its boundaries. Foreground Mattes are similar to Despill Mattes, but with one key difference: it doesn’t turn everything gray that has the color of your keyer.

Using the same example as above, shooting out windows with green screen behind it, if there were to be a green plant, not overlapping the green screen on the set.   The plant would normally be turned gray.  To correct this and keep the green plant green, you may draw a matte around the plant and set that matte to “Foreground.”