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Overview of the SynthDet Unity Project

This project utilizes the Unity Perception package for randomizing the environment and generating ground-truth on each frame.

Ground truth generation

To generate ground truth, the Perception Camera is used, which is a pre-built component available in the Perception package. This special type of camera accepts a list of Labelers, each of which is capable of generating a specific type of ground truth. To speed up your workflow, the Perception package comes with several common labelers for object-detection and human keypoint labeling tasks; however, if you are comfortable with code, you can also add your own custom Labelers. SynthDet uses Labelers for 2D bounding boxes, object count and pixel count information, semantic segmentation, and reporting of metadata on various randomized parameters.

To see the list of Labelers attached to your Perception Camera, select the Perception Camera GameObject in the Scene Hierarchy window.

Domain randomization

The Perception package comes with a randomization toolset that makes it easy to coordinate simulations in which environments are continually randomized. Simulations are coordinated by Scenarios, which run a set of Randomizers in a deterministic order. Each Randomizer is then tasked with randomizing a certain aspect of the environment. Randomizers are flexible and extensible, making it easy for users to create their own custom randomization strategies.

To check out the list of Randomizers used in the SynthDet project, select the Scenario GameObject inside the SynthDet Scene. The Inspector window will then look like this:

Besides the list of Randomizers, you also see several properties for the Scenario. The Random Seed set here is the seed used for all randomizations that happen throughout the Scenario, in all Randomizers. If you only use the provided randomization toolset for generating random values throughout your project's C# code, you are guaranteed to have identical outputs between simulations that use the same exact Randomizers and Random Seed value. Each Scenario comprises a number of Iterations and each Iteration can be run for a number of frames. Randomizers can be scripted to perform operations at different times, including when the simulation first starts, the start or end of each Iteration, or on each frame of each Iteration. Total Iterations and Frames Per Iteration control how many Iterations the Scenario performs and how many frames each Iteration runs for.

In the above screenshot, the UI for all Randomizers is collapsed. Most Randomizers come with properties and parameters that you can modify. To modify a Randomizer, you just need to expand its UI by clicking the small triangle icon to the left of its name, like below:

Here is what each Randomizer in SynthDet does:

  • BackgroundObjectPlacementRandomizer
    • The background consists of a large number of primitive shapes with randomized positions, rotations, textures, and hue offsets. The purpose of this background is to act as distraction for the machine learning model. This Randomizer has the task of instantiating and positioning these primitive shapes.
  • ForegroundObjectPlacementRandomizer
    • This Randomizer instantiates and positions the foreground objects. These are the grocery objects, for which we generate bounding boxes.
  • ForegroundScaleRandomizer
    • Assigns random scales to each of the foreground (grocery) objects.
  • ForegroundOccluderPlacementRandomizer
    • Another distraction for the model comes in the form of shapes that are placed between the camera and the objects that are to be detected (the grocery objects). These occluders are randomized in position, scale, texture, and hue offset. This Randomizer is tasked with instantiating and positioning them.
  • ForegroundOccluderScaleRandomizer
    • Randomizes the scale of the foreground occluder objects.
  • TextureRandomizer
    • Randomizes the textures of the background shapes and foreground occluder objects.
  • HueOffsetRandomizer
    • Randomizes the hue offset of the background shapes and foreground occluder objects.
  • RotationRandomizer
    • The background shapes, foreground occluder objects, and one of the four directional lights present in the Scene are rotated randomly using this Randomizer.
  • UnifiedRotationRandomizer
    • This Randomizer assigns a random rotation to all foreground (grocery) objects. The difference between this and RotationRandomizer is that here, the same rotation is applied to all target objects.
  • VolumeRandomizer
    • Randomizes the contrast, saturation, and blur of RGB output images.
  • LightRandomizer
    • Randomizes the Directional Light object in the Scene.