Built-in Operators and Extensions

The units of work of Holoscan applications are implemented within Operators, as described in the core concepts of the SDK. The operators included in the SDK provide domain-agnostic functionalities such as IO, machine learning inference, processing, and visualization, optimized for AI streaming pipelines, relying on a set of Core Technologies.

Operators

The operators below are defined under the holoscan::ops namespace for C++ and CMake, and under the holoscan.operators module in Python.

Class	CMake target/lib	Documentation
AJASourceOp	`aja`	`C++`/`Python`
BayerDemosaicOp	`bayer_demosaic`	`C++`/`Python`
FormatConverterOp	`format_converter`	`C++`/`Python`
HolovizOp	`holoviz`	`C++`/`Python`
InferenceOp	`inference`	`C++`/`Python`
InferenceProcessorOp	`inference_processor`	`C++`/`Python`
PingRxOp	`ping_rx`	`C++`/`Python`
PingTxOp	`ping_tx`	`C++`/`Python`
SegmentationPostprocessorOp	`segmentation_postprocessor`	`C++`/`Python`
VideoStreamRecorderOp	`video_stream_recorder`	`C++`/`Python`
VideoStreamReplayerOp	`video_stream_replayer`	`C++`/`Python`
V4L2VideoCaptureOp	`v4l2`	`C++`/`Python`

Given an instance of an operator class, you can print a human-readable description of its specification to inspect the inputs, outputs, and parameters that can be configured on that operator class:

C++
Python

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            std::cout << operator_object->spec()->description() << std::endl;

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            print(operator_object.spec)

Note

The Holoscan SDK uses meta-programming with templating and std::any to support arbitrary data types. Because of this, some type information (and therefore values) might not be retrievable by the description API. If more details are needed, we recommend inspecting the list of Parameter members in the operator header to identify their type.

Extensions

The Holoscan SDK also includes some GXF extensions with GXF codelets, which are typically wrapped as operators, or present for legacy reasons. In addition to the core GXF extensions (std, cuda, serialization, multimedia) listed here, the Holoscan SDK includes the following GXF extensions:

bayer_demosaic
gxf_holoscan_wrapper
opengl
stream_playback
ucx_holoscan

Bayer Demosaic

The bayer_demosaic extension includes the nvidia::holoscan::BayerDemosaic codelet. It performs color filter array (CFA) interpolation for 1-channel inputs of 8 or 16-bit unsigned integer and outputs an RGB or RGBA image. It is wrapped by the nvidia::holoscan::ops::BayerDemosaicOp operator.

Note

The BayerDemosaicOp will be converted to a native operator in future releases.

GXF Holoscan Wrapper

The gxf_holoscan_wrapper extension includes the holoscan::gxf::OperatorWrapper codelet. It is used as a utility base class to wrap a holoscan operator to interface with the GXF framework.

Learn more about it in the Using Holoscan Operators in GXF Applications section.

OpenGL

The opengl_renderer extension includes the nvidia::holoscan::OpenGLRenderer codelet. It displays a VideoBuffer, leveraging OpenGL/CUDA interop.

Warning

This codelet is deprecated, and will be removed in a future release in favor of a the holoviz operator.

Parameter	Description	Type
signal	Input Channel	`gxf::Handle<gxf::Receiver>`
width	Width of the rendering window	`unsigned int`
height	Height of the rendering window	`unsigned int`
window_close_scheduling_term	`BooleanSchedulingTerm` to stop the codelet from ticking after all messages are published	`gxf::Handle<gxf::BooleanSchedulingTerm>`

Stream Playback

The stream_playback extension includes the nvidia::holoscan::stream_playback::VideoStreamSerializer entity serializer to/from a Tensor Object. This extension does not include any codelets: reading and writing video stream (gxf entity files) from the disk was implemented as native operators with VideoStreamRecorderOp and VideoStreamReplayerOp, though they leverage the VideoStreamSerializer from this extension.

Note

The VideoStreamSerializer codelet is based on the nvidia::gxf::StdEntitySerializer with the addition of a repeat feature. (If the repeat parameter is true and the frame count is out of the maximum frame index, unnecessary warning messages are printed with nvidia::gxf::StdEntitySerializer.)

UCX (Holoscan)

The ucx_holoscan extension includes nvidia::holoscan::UcxHoloscanComponentSerializer which is a nvidia::gxf::ComponentSerializer that handles serialization of holoscan::Message and holoscan::Tensor types for transmission using the Unified Communication X (UCX) library. UCX is the library used by Holoscan SDK to enable communication of data between fragments in distributed applications.

Note

The UcxHoloscanComponentSerializer is intended for use in combination with other UCX components defined in the GXF UCX extension. Specifically, it can be used by the UcxEntitySerializer where it can operate alongside the UcxComponentSerializer that serializes GXF-specific types (nvidia::gxf::Tensor, nvidia::gxf::VideoBuffer, etc.). This way both GXF and Holoscan types can be serialized by distributed applications.

HoloHub

Visit the HoloHub repository to find a collection of additional Holoscan operators and extensions.