User Manual

Domain of Definition and
Region of Interest
As a compositing environment, the Fusion page uses the standard compositing conventions of
Region of Interest (RoI) and Domain of Definition (DoD) to dramatically improve performance.
Domain of Definition (DoD)
In compositing, the Domain of Definition, frequently abbreviated to DoD, refers to a rectangular
region that defines what part of an image actually contains data. DoD makes the concept of an
image’s actual frame somewhat flexible, since rendering is no longer limited to the actual width
and height of the image. This has two effects on the way Fusion renders images.
Firstly, nodes will no longer be required to render portions of the image that will not be affected
by the node. This helps the renderer to optimize its performance. Secondly, Fusion can now
keep track of and apply a node’s effect to pixels that lie outside the visible portion of the image.
For example, consider the output of a Text+ node rendered against a transparent background.
The text occupies only a portion of the pixels in the image. Without Domain of Definition, you
would be required to process every pixel in the image needlessly. With a DoD, you are able to
optimize effects applied to the image, producing faster results and consuming less memory in
the process.
The following image shows an image with the DoD outlined.
The DoD is shown as two XY coordinates indicating
the corners of an axis-aligned bounding box (in pixels).
For the most part, the DoD is calculated automatically and without the need for manual
intervention. For example, all the nodes in the Generator category automatically generate the
correct DoD. For nodes like Fast Noise, Mandelbrot, and Background, this is usually the full
dimensions of the image. In the case of Text+ and virtually all of the Mask nodes, the DoD will
often be much smaller or larger.
The OpenEXR format is capable of storing the data window of the image, and Fusion will apply
this as the DoD when loading such an image through a Loader node and will write out the DoD
through the Saver node.
When using the Fusion page in DaVinci Resolve, clips from the Edit page timeline or Media Pool
will typically have the DoD default to the full image width of the source media. The exception is
media stored in OpenEXR format.
The DoD is established as soon as the image is created or loaded into the composition. From
there, it passes downstream, where viewers combine it with their Region of Interest in order to
determine exactly what pixels should be affected by the node. As you work, different nodes will
automatically shrink, expand, or move the DoD as they apply their effect to an image, causing
the DoD to change from node to node.
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