An Alpha Matte is a black and white piece of footage that instructs a program what is transparent or opaque. Think of a family photo – say you took that photo of you and your family in your living room, but you wish you could place them in a more exciting environment. By creating an alpha matte you can instruct a program, such as Adobe After Effects, to only see you and your family and make the background completely transparent. Thus, allowing you to insert a new and exciting background – outer space, the jungle, Paris, etc. I will show you how to create an alpha matte using Silhouette FX in three simple steps:
– Setting up a New Session
– Creating the Alpha Matte
– Exporting the Alpha Matte
SETTING UP A NEW SESSION
When you first open Silhouette FX you will need to import the footage you intend to roto – this may be a video clip or a sequence of JPEGs or DPX images. For this example I will be creating an alpha matte from a single image. To import the footage go to FILE > IMPORT > MEDIA, and then navigate to the desired footage and select OPEN.
You will notice the footage is then added to your PROJECT PANEL for visual reference. At this point, you need to open a new session with this media before you can start to create your matte – think of a new session as a new composition if you are more familiar with an Adobe After Effects pipeline. To create a new session, simply go to SESSION in the top toolbar and select NEW SESSION (or hotkey COMMAND + N). An info window will pop up allowing you to name the session and adjust any settings needed. For this training exercise, keep all the default settings and leave only ROTO checked as the available Node.
CREATING THE ALPHA MATTE
Now that you are ready to create the alpha matte you will notice a set of tools located on the upper left hand side of the canvas window.
About halfway down that list you will see an icon that looks like a dot with a curved line and an x – this is the X SPLINE TOOL. Just beneath that is the BEZIER TOOL.
Both tools are sufficient in completing this task. If you use Photoshop you most likely already know all the subtleties and tricks behind them. I find the X Spline tool better suited for rotoscoping human anatomy. However, if you intend to export your matte to composite into NUKE, there tends to be some ingest errors as X Splines are not supported in NUKE and, in turn, attempts to be converted into faulty Beziers.
To use either tool simply click and select it from the tool set, navigate over the canvas image and click to create an ANCHOR POINT. Move your mouse and click again to create a second ANCHOR POINT. Now you’ll notice a line is connecting the two points. Continue to click around to create your desired shape and finish by returning to the first anchor point you created. Click on it one final time to close and create an OBJECT.
OBJECTS you create are then stored in the OBJECT LIST window located to the right of your screen.
You will also notice in the lower right of the OBJECT LIST window is a ‘+” icon – if you click on it you will create a LAYER. You can highlight shapes and drag and store them in these layers you create. Layers are helpful to help sort all of the objects you create for quick reference and control.
It’s good to break your image down into a series of objects instead of trying to outline the entire subject with one giant outline. It is easier to make adjustments to isolated shapes.
EXPORTING THE ALPHA MATTE
Once your alpha matte is finished, you are ready to export. Simply go to SESSION > RENDER SESSION (or hotkey COMMAND + R).
You will be presented with a Render Options window. To ensure you are getting just the alpha matte, uncheck COLOR and make sure ALPHA is the only format checked. For format type, use the drop down menu to select TIFF. Change the range to CURRENT FRAME. Finally, to finish under output, you can select the three dots next to DIRECTORY to be able to set your render destination, input a FILENAME, and hit APPLY.
You have now successfully created and exported your alpha matte. From here, you can import the matte into another software program, such as Adobe After Effects, and combine the matte with the original image in order to eliminate the background and continue to composite as needed.