Crop and Resize Objects

How does secondary GIE crop and resize objects?

SGIE will crop the object from NvStreamMux buffer using the object’s bbox detected by the Primary GIE.

The crop is then scaled/converted to the network resolution/color format.

For example, if the NvStreamMux resolution is 1920x1080, SGIE will crop using object bbox co-ordinates

(e.g. x=1000, y=20, w=400, y=500) from the 1920x1080 image and then scale it to the SGIE network resolution (say 224x224).

In practice, the object crop + scaling + color conversion happens in one go.

 

How to save frames from GstBuffer?

To save frames from gst buffer you need to Map gst buffer using gst_buffer_map () API.

Here is the pseudo code:

GstMapInfo in_map_info;
NvBufSurface *surface = NULL;

memset(&in_map_info, 0, sizeof(in_map_info));
if (!gst_buffer_map(inbuf, &in_map_info, GST_MAP_READ)) {
    g_print ("Error: Failed to map gst buffer\n");
}
surface = (NvBufSurface*)in_map_info.data;

Now that you have access to NvBufSurface structure, you can access actual frame memory and save it.

At the end you need to unmap gst buffer using gst_buffer_unmap (inbuf, &in_map_info)

For more details, see gst_dsexample_transform_ip() in gst-dsexample plugin source code.