Prediction with ONNX Models

Similar to the steps in the quick start guide using an OpenVINO IR model format. Model Server accepts ONNX models with the same versioning structure. Similar to IR, place each ONNX model file in a separate model version subdirectory. Below is a complete functional use case using python 3.6 or higher.

Download the model:

curl -L --create-dir -o resnet/1/resnet50-caffe2-v1-9.onnx
tree resnet/
└── 1
    └── resnet50-caffe2-v1-9.onnx

Note that the downloaded model requires an additional preprocessing function. Preprocessing can be performed in the client by manipulating data before sending the request. Preprocessing can be also delegated to the server by creating a DAG, and using a custom processing node. Both methods will be explained below.

Option 1: Adding preprocessing to the client side

Option 2: Adding preprocessing to the server side (building DAG)

Get an image to classify:

wget -q

Install python libraries:

pip install -r

Get the list of imagenet classes:


Option 1: Adding preprocessing to the client side

Start the OVMS container with single model instance:

docker run -d -u $(id -u):$(id -g) -v $(pwd)/resnet:/model -p 9001:9001 openvino/model_server:latest \
--model_path /model --model_name resnet --port 9001

Run inference request with a client containing preprocess function presented below:

import numpy as np
import cv2
import grpc
from tensorflow_serving.apis import predict_pb2
from tensorflow_serving.apis import prediction_service_pb2_grpc
from tensorflow import make_tensor_proto, make_ndarray
import classes

def preprocess(img_data):
    mean_vec = np.array([0.485, 0.456, 0.406])
    stddev_vec = np.array([0.229, 0.224, 0.225])
    norm_img_data = np.zeros(img_data.shape).astype('float32')
    for i in range(img_data.shape[0]):
        # for each pixel in each channel, divide the value by 255 to get value between [0, 1] and then normalize
        norm_img_data[i,:,:] = (img_data[i,:,:]/255 - mean_vec[i]) / stddev_vec[i]
    return norm_img_data

def getJpeg(path, size):
    with open(path, mode='rb') as file:
        content =

    img = np.frombuffer(content, dtype=np.uint8)
    img = cv2.imdecode(img, cv2.IMREAD_COLOR)  # BGR format
    # format of data is HWC
    # add image preprocessing if needed by the model
    img = cv2.resize(img, (224, 224))
    img = img.astype('float32')
    #convert to NCHW
    img = img.transpose(2,0,1)
    # normalize to adjust to model training dataset
    img = preprocess(img)
    img = img.reshape(1,3,size,size)
    print(path, img.shape, "; data range:",np.amin(img),":",np.amax(img))
    return img

img1 = getJpeg('bee.jpeg', 224)

channel = grpc.insecure_channel("localhost:9001")
stub = prediction_service_pb2_grpc.PredictionServiceStub(channel)

request = predict_pb2.PredictRequest() = "resnet"
request.inputs["gpu_0/data_0"].CopyFrom(make_tensor_proto(img1, shape=(img1.shape)))
result = stub.Predict(request, 10.0) # result includes a dictionary with all model outputs

output = make_ndarray(result.outputs["gpu_0/softmax_1"])
max = np.argmax(output)
print("Class is with highest score: {}".format(max))
print("Detected class name: {}".format(classes.imagenet_classes[max]))

It shows the following output:

bee.jpeg (1, 3, 224, 224) ; data range: -2.117904 : 2.64
Class is with highest score: 309
Detected class name: bee

Option 2: Adding preprocessing to the server side (building a DAG)

Create a configuration file with DAG containing two sequential nodes: one being the image transformation node and one DL model node resnet. The job of the image transformation node will be to preprocess the image data to match format required by the ONNX model resnet50-caffe2-v1-9.onnx.

The example configuration file is available in image transformation custom node directory.

Image transformation custom node library building steps can be found here.

Prepare workspace with the model, preprocessing node library and configuration file.

$ tree workspace

├── config_with_preprocessing_node.json
├── lib
└── models
    └── resnet50-caffe2-v1
        └── 1
            └── resnet50-caffe2-v1-9.onnx

Start the OVMS container with a configuration file option:

docker run -d -u $(id -u):$(id -g) -v $(pwd)/workspace:/workspace -p 9001:9001 openvino/model_server:latest \
--config_path /workspace/config_with_preprocessing_node.json --port 9001

Use a sample client to send JPEG images to the server:

$ cd model_server/example_client

$ python3 --grpc_port 9001 --input_name 0 --output_name 1463 --model_name resnet --batchsize 1

Below is the client output including performance and accuracy results:

Start processing:
        Model name: resnet
        Images list file: input_images.txt
Batch: 0; Processing time: 21.52 ms; speed 46.47 fps
         1 airliner 404 ; Correct match.
Batch: 1; Processing time: 17.50 ms; speed 57.14 fps
         2 Arctic fox, white fox, Alopex lagopus 279 ; Correct match.
Batch: 2; Processing time: 14.91 ms; speed 67.05 fps
         3 bee 309 ; Correct match.
Batch: 3; Processing time: 11.66 ms; speed 85.76 fps
         4 golden retriever 207 ; Correct match.
Batch: 4; Processing time: 12.88 ms; speed 77.66 fps
         5 gorilla, Gorilla gorilla 366 ; Correct match.
Batch: 5; Processing time: 14.34 ms; speed 69.74 fps
         6 magnetic compass 635 ; Correct match.
Batch: 6; Processing time: 13.14 ms; speed 76.12 fps
         7 peacock 84 ; Correct match.
Batch: 7; Processing time: 14.48 ms; speed 69.04 fps
         8 pelican 144 ; Correct match.
Batch: 8; Processing time: 12.71 ms; speed 78.71 fps
         9 snail 113 ; Correct match.
Batch: 9; Processing time: 17.23 ms; speed 58.03 fps
         10 zebra 340 ; Correct match.
Overall accuracy= 100.0 %
Average latency= 14.5 ms

Node parameters explanation

Additional preprocessing step applies a division and an subtraction to each pixel value in the image. This calculation is configured by passing two parameters to image transformation custom node:

"params": {
  "mean_values": "[123.675,116.28,103.53]",
  "scale_values": "[58.395,57.12,57.375]",

For each pixel, the custom node subtracts 123.675 from blue value, 116.28 from green value and 103.53 from red value. Next, it divides in the same color order using 58.395, 57.12, 57.375 values. This way we match the image data to the input required by the ONNX model.