[MMDetection](https://github.com/open-mmlab/mmdetection) aka `mmdet` is an open source object detection toolbox based on PyTorch. It is a part of the [OpenMMLab](https://openmmlab.com/) project.
## Installation
### Install mmdet
Please follow the [installation guide](https://mmdetection.readthedocs.io/en/3.x/get_started.html) to install mmdet.
### Install mmdeploy
There are several methods to install mmdeploy, among which you can choose an appropriate one according to your target platform and device.
You can use [tools/deploy.py](https://github.com/open-mmlab/mmdeploy/blob/1.x/tools/deploy.py) to convert mmdet models to the specified backend models. Its detailed usage can be learned from [here](../02-how-to-run/convert_model.md).
It is crucial to specify the correct deployment config during model conversion. We've already provided builtin deployment config [files](https://github.com/open-mmlab/mmdeploy/tree/1.x/configs/mmdet) of all supported backends for mmdetection, under which the config file path follows the pattern:
There are two of them. One is `detection` and the other is `instance-seg`, indicating instance segmentation.
mmdet models like `RetinaNet`, `Faster R-CNN` and `DETR` and so on belongs to `detection` task. While `Mask R-CNN` is one of `instance-seg` models. You can find more of them in chapter [Supported models](#supported-models).
**DO REMEMBER TO USE**`detection/detection_*.py` deployment config file when trying to convert detection models and use `instance-seg/instance-seg_*.py` to deploy instance segmentation models.
- **{backend}:** inference backend, such as onnxruntime, tensorrt, pplnn, ncnn, openvino, coreml etc.
- **{precision}:** fp16, int8. When it's empty, it means fp32
- **{static | dynamic}:** static shape or dynamic shape
- **{shape}:** input shape or shape range of a model
Therefore, in the above example, you can also convert `faster r-cnn` to other backend models by changing the deployment config file `detection_onnxruntime_dynamic.py` to [others](https://github.com/open-mmlab/mmdeploy/tree/1.x/configs/mmdet/detection), e.g., converting to tensorrt-fp16 model by `detection_tensorrt-fp16_dynamic-320x320-1344x1344.py`.
When converting mmdet models to tensorrt models, --device should be set to "cuda"
```
## Model specification
Before moving on to model inference chapter, let's know more about the converted model structure which is very important for model inference.
The converted model locates in the working directory like `mmdeploy_models/mmdet/ort` in the previous example. It includes:
```
mmdeploy_models/mmdet/ort
├── deploy.json
├── detail.json
├── end2end.onnx
└── pipeline.json
```
in which,
- **end2end.onnx**: backend model which can be inferred by ONNX Runtime
- \***.json**: the necessary information for mmdeploy SDK
The whole package **mmdeploy_models/mmdet/ort** is defined as **mmdeploy SDK model**, i.e., **mmdeploy SDK model** includes both backend model and inference meta information.
## Model inference
### Backend model inference
Take the previous converted `end2end.onnx` model as an example, you can use the following code to inference the model and visualize the results.
```python
from mmdeploy.apis.utils import build_task_processor
from mmdeploy.utils import get_input_shape, load_config
Besides python API, mmdeploy SDK also provides other FFI (Foreign Function Interface), such as C, C++, C#, Java and so on. You can learn their usage from [demos](https://github.com/open-mmlab/mmdeploy/tree/dev-1.x/demo).
