GstInference with TinyYoloV2 architecture

GstInference
Introduction
Getting started
Getting the code Building the plugin Quick Starting Guide
Supported architectures
InceptionV1 InceptionV2 InceptionV3 InceptionV4 TinyYoloV2 TinyYoloV3 YoloV2 ResNetV1 MobileNetV2 MobileNetV2 + SSD AlexNet
Supported backends
TensorFlow Tensorflow-Lite Coral from Google Caffe TensorRT ONNXRT ONNXRT ACL ONNXRT OpenVINO
Metadata and Signals
GstClassificationMeta GstInferenceMeta Signals
Overlay Elements
Inference Overlay
Utils Elements
InferenceFilter InferenceCrop InferenceDebug InferenceBin
Legacy pipelines
PC NANO TX2 Xavier IMX8
Example pipelines
Example applications
Classification Detection Hand Pose Recognition
Benchmarks
Model Zoo
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Description

TinyYOLO (also called tiny Darknet) is the light version of the YOLO(You Only Look Once) real-time object detection deep neural network. TinyYOLO is lighter and faster than YOLO while also outperforming other light model's accuracy. The following table presents a comparison between YOLO, Alexnet, SqueezeNet, and tinyYOLO.

Model	Top-1	Top-5	Ops	Size
AlexNet	57.0	80.3	2.27 Bn	238 MB
Darknet	61.1	83.0	0.81 Bn	28 MB
SqueezeNet	57.5	80.3	2.17 Bn	4.8 MB
Tiny Darknet	58.7	81.7	0.98 Bn	4.0 MB

TinyYOLO results are also very similar to YOLO's. The following image compares both results:

TinyYOLO results vs YOLO results

Architecture

The YOLO detection network has 24 convolutional layers followed by 2 fully connected layers. It uses alternating 1×1 convolutional layers to reduce the feature space between layers. The convolutional layers are pretrained on the ImageNet classification task at half the resolution (224 × 224 input image) and then the resolution is doubled for the detection training.

YOLO architecture

Tiny YOLO operates on the same principles as YOLO but with a reduced number of parameters. It has only 9 convolutional layers, compared to YOLO's 24.

TinyYOLO architecture

GStreamer Plugin

The GStreamer plugin uses the pre-process and post-process described in the original paper. Please take into consideration that not all deep neural networks are trained the same even if they use the same model architecture. If the model is trained differently, details like label ordering, input dimensions, and color normalization can change.

This element was based on the ncappzoo repo. The pre-trained model used to test the element may be downloaded from our R2I Model Zoo for the different frameworks.

Properties

Property	Value	Description
backend	Enum (0,1)	0: ncsdk 1: tensorflow
model-location	String	Path to the model to use
object-threshold	Double [0,1]	Objectness threshold
probability-threshold	Double [0,1]	Class probability threshold
iou-threshold	Double [0,1]	Intersection over union threshold to merge similar boxes

Pre-process

Input parameters:

• Input size: 416 x 416
• Format RGB

The pre-process consists of taking the input image and transforming it to the input size (by scaling, interpolation, cropping...) and dividing each pixel channel value by 255.

Post-process

Output parameters:

• Grid dimensions: 13x13
• Grid cell dimensions: 32x32 px
• Number of classes: 20
• Labels: ["aeroplane", "bicycle", "bird", "boat", "bottle", "bus", "car", "cat", "chair", "cow", "diningtable", "dog", "horse", "motorbike", "person", "pottedplant", "sheep", "sofa", "train", "tvmonitor"]
• Anchors: [1.08, 1.19, 3.42, 4.41, 6.63, 11.38, 9.42, 5.11, 16.62, 10.52]
• Number of boxes per cell: 5
• Box dim: 4 [x_center, y_center, width, height]
• Objectness threshold: 0.08 (configurable)
• Probability threshold: 0.08 (configurable)
• Intersection over union threshold: 0.30 (configurable)

The post-process of the YOLO network is a lot more complex than the pre-process:

• Convert the tensor to have shape = 13x13x5x25 = grid_cells x n_boxes_in_each_cell x n_predictions_for_each_box
• The 25 predictions are: 2 coordinates and 2 shape values (x,y,h,w), 1 Objectness score, 20 Class scores

Each resulting box needs to be scale by an anchor and the grid size. The post-process considers only probabilities that surpass the user-defined objectness threshold (0.08) and class probability threshold (0.08). Then it extracts the boxes from the final part of the array corresponding to the probabilities above the threshold. An example result can be seen in the following image:

First step of TinyYOLO postprocess

Now an algorithm is needed to remove or merge duplicated boxes. We use the intersection over union metric to determine that 2 boxes that surpass a configurable intersection over union threshold (0.35) on this metric are considered the same object. Then, we keep the object with the highest probability and remove the other one. The final result can be seen in the following figure:

Final step of TinyYOLO postprocess

Examples

Please refer to the TinyYOLO section on the examples page.