imageprocessing/motion/denseopticalflow/docs/usecase1.md

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# Copyright (c) 2019-2020, NVIDIA CORPORATION.  All rights reserved.

@page denseopticalflow_usecase1 Dense Optical Flow Workflow

@note SW Release Applicability: This tutorial is applicable to modules in both **NVIDIA DriveWorks** and **NVIDIA DRIVE Software** releases.

#### Initialization

NVIDIA<sup>&reg;</sup> DriveWorks includes a sample pipeline demonstrating the Dense Optical Flow module across multiple video frames. The following summarizes the sample's initialization steps:

Initialize the parameters for the module with default values:

```{.cpp}
    dwDenseOpticalFlowParameters params;
    dwDenseOpticalFlow_initDefaultParams(&params);
```

Select the processors for the corresponding stages to run on:

```{.cpp}
    params.processorNVENC = DW_PROCESSOR_TYPE_NVENC_0;
    params.processorPVA = DW_PROCESSOR_TYPE_PVA_0;
```

Set input image size dimensions:

```{.cpp}
    params.imageWidth = 1280;
    params.imageHeight = 800;
```

Initialize the Dense Optical Flow module:

```{.cpp}
    dwDenseOpticalFlowHandle_t dof;
    dwDenseOpticalFlow_initialize(&dof, &params, sdk);
```

Finally, the output image must be allocated by the application. This can be achieved by acquiring the required properties and 
using the dwImage API:

```{.cpp}
    dwImageProperties outputProperties;
    dwDenseOpticalFlow_getOutputImageProperties(&outputProperties, dof);

    dwImageHandle_t outputImage;
    dwImage_create(&imageOutput, outputProperties, sdk);
```

#### Process

DriveWorks accepts two images as input: a reference image, and a template image. These two are used to compute the motion vectors.

The input images must have the following format: `::DW_IMAGE_FORMAT_YUV420_UINT8_SEMIPLANAR`.

The output image has the following format: `::DW_IMAGE_FORMAT_RG_INT16. The R and G channels represent motion in the X and Y dimensions, respectively.

```{.cpp}
    dwDenseOpticalFlow_calculateOpticalFlow(outputImage,
                                            imageYUV420,
                                            imageRefYUV420,
                                            dof);
```

#### Release

Finally, release the resources used:

```{.cpp}
    dwImage_destroy(imageOutput);
    dwDenseOpticalFlow_release(dof);
```

For a demonstration of this workflow, see @ref dwx_denseopticalflow_sample.