OFA Gridsize and NumOfLevels

[maximilian.reeg.p]

Hello,
when i try to calculate the dense optical flow in cpp with vpi it is only possible to do so with a gridsize of 2 and numoflevels of 4. When i change the grid size to 4 i receive VPI_ERROR_INVALID_ARGUMENT from the function vpiCreateOpticalFlowDense(). Can somebody explain me why?

[AastaLLL]

Hi,

Could you share the input image size with us?
The output flow need to bigger than 4x4.

Thanks.

[maximilian.reeg.p]

The input image is a 8bit grayscale image with 640 times 480 pixel.

[AastaLLL]

Hi,

Based on your image size, the pyramid sizes are:
640x480 - 160x120 - 40x30 - 10x7

Which is too small, the pyramid size also needs to be larger than 32 to get a flow.

Thanks.

[maximilian.reeg.p]

Thank you. Can you also tell me how i can split the output of the dense optical flow in the VPIImage with the format VPI_IMAGE_FORMAT_2S16_BL to two seperate VPIImages with the format VPI_IMAGE_FORMAT_S16?

[AastaLLL]

Hi,

You can do this with OpenCV.
The example can be found in the /opt/nvidia/vpi2/samples/13-optflow_dense.

VPIImageData mvData;
CHECK_STATUS(vpiImageLockData(mvImg, VPI_LOCK_READ, VPI_IMAGE_BUFFER_HOST_PITCH_LINEAR, &mvData));

...
cv::Mat magnitude, angle;
{
    cv::Mat flowChannels[2];
    split(flow, flowChannels);

Thanks.