Explorer/RaspberryPi/Visualprocessing/Motionvector

The Raspberry Pi is based on a BCM2835 System on a Chip (SoC), which provides an hardware (GPU) motion estimation block to the H264 encoder.
The Coarse Motion Block (CME) compares macroblock (16×16 pixels) from two consecutive frames and output a vector where the macroblock came from.
The vector is encoded in a single 32-bit value:
- the most significant 16 bits represent a Sum of Absolute Differences (SAD = quality of the estimation, the lower is the better)
- the others 16 bits represents (8-bit signed integer) the horizontal and vertical directions

The code below, patch "raspivid" to provide a video buffer (gray scale image) with motion vectors.
The new code compile as "raspicv", with a custom "cv.cpp" (see below), output video stream with motion vector display to /tmp/camera3 The "cv.cpp" is limited to 640x480 grayscale image in this sample.

Adam Heinrich thesis An Optical Flow Odometry Sensor Based on the Raspberry Pi Computer

git clone https://github.com/raspberrypi/userland.git
git clone https://github.com/adamheinrich/RaspiCV.git

Path RaspiCV/src/Makefile

< USERLAND_DIR
> USERLAND_DIR = $(HOME)/userland
...
>      $(USERLAND_DIR)/host_applications/linux/apps/raspicam/RaspiHelpers.c \
>      $(USERLAND_DIR)/host_applications/linux/apps/raspicam/RaspiCommonSettings.c \
>      $(USERLAND_DIR)/host_applications/linux/apps/raspicam/RaspiGPS.c \
>      $(USERLAND_DIR)/host_applications/linux/apps/raspicam/libgps_loader.c
...
< CXXFLAGS = $(ARCHFLAGS) $(DBGFLAGS) $(OPTFLAGS) `pkg-config --cflags opencv` \
> CXXFLAGS = $(ARCHFLAGS) $(DBGFLAGS) $(OPTFLAGS) `pkg-config --cflags opencv4` \
...
< LDFLAGS += `pkg-config --libs opencv`
> LDFLAGS += `pkg-config --libs opencv4`
...
< LDLIBFLAGS = -Wl, ...
> LDLIBFLAGS = -ldl -Wl, ...

Update RaspiCV.c

cp userland/host_applications/linux/apps/raspicam/RaspiVid.c ~/RaspiCV/src/RaspiCV.c

and patch it

< #include <semaphore.h>
> #include "cv.h"
  #include <semaphore.h>
...
              if(pData->pstate->inlineMotionVectors)
              {
>		 cv_process_imv(buffer->data, buffer->length, buffer->pts);
                 bytes_written = fwrite(buffer->data, 1, buffer->length, pData->imv_file_handle);
...
     if (bytes_to_write)
     {
        mmal_buffer_header_mem_lock(buffer);
>	cv_process_img(buffer->data, bytes_to_write, buffer->pts);
        bytes_written = fwrite(buffer->data, 1, bytes_to_write, pData->raw_file_handle);
...
>             cv_init(state.common_settings.width, state.common_settings.height, state.framerate, state.raw_output_fmt);
              int initialCapturing=state.bCapturing;
              while (running)
              {
...
...
     destroy_splitter_component(&state);
     destroy_camera_component(&state);

>    cv_close();

Replace de file RaspiCV/src/cv.cpp with this

#include "cv.h"
#include <opencv2/opencv.hpp>
#include <pthread.h>

using namespace cv;
using namespace std;

/*****************************************************************************/
#define SAD_LIMIT 150
#define SCALE 3/2
#define streamOutGstStr "appsrc ! shmsink socket-path=/tmp/camera3 wait-for-connection=false async=false sync=false"

/*****************************************************************************/
struct motion_elt_t {
  int8_t x;
  int8_t y;
  uint16_t sad;
};
static motion_elt_t *motionIn;
static Mat imageIn;
static int width,height,fps; 

static pthread_mutex_t imv_mutex;
static bool imv_ready=false; 

static pthread_t img_thread;
static pthread_mutex_t img_mutex;
static pthread_cond_t img_condv;
static bool img_ready=false; 

static bool init_ready=false; 

/*****************************************************************************/
static void *process_thread(void *ptr)
{
  VideoWriter strOut = VideoWriter(streamOutGstStr,0,fps/1,Size(width,height),true); 

  unsigned int imageSize = ((width * height * sizeof(uint8_t))*SCALE);
  Mat imageOut(width, height, CV_8UC3,Scalar(0,0,0));
  char* imgptr = imageOut.ptr<char>(0); 

  int mbx = width/16;
  int mby = height/16;
  unsigned int motionSize = ((mbx+1)*mby) * sizeof(struct motion_elt_t); 
  motion_elt_t *motionOut = new motion_elt_t[(mbx+1)*mby];
  unsigned int uoffset=(width * height);
  unsigned int voffset=uoffset*5/4; 
 
  unsigned int k,l,m,s;
  int x,y,p,q,a,b;
  int8_t r;

  int8_t mline[17][17];
  for(int y=0;y<=16;y++) {
    for(int x=0;x<=16;x++) {
      mline[x][y]=floor((x*y/16.0)+0.5);
    }
  }

  while (true) {
    pthread_mutex_lock(&img_mutex);
    while (!img_ready) pthread_cond_wait(&img_condv, &img_mutex);
    memcpy(imageOut.data,imageIn.data,imageSize);		
    img_ready=false;
    pthread_mutex_unlock(&img_mutex); 

    if(imv_ready) { 
      pthread_mutex_lock(&imv_mutex);
      memcpy(motionOut ,motionIn, motionSize);
      imv_ready=false;
      pthread_mutex_unlock(&imv_mutex);
    } 

    for (int j=1;j<(mby-1);j++) {
      for (int i=1;i< (mbx-1);i++) { 

   	 x=((i-1)*8)+12;
        y=((j-1)*8)+12;
        k=(2*((y*(mbx)*16)+x));
        imgptr[k]=0;
 
        l=(y*(mbx)*8)+x;
        m = (l & 1) ? 0xFF : 0x00;
        imgptr[uoffset+l] = imgptr[uoffset+l] & m;
        imgptr[voffset+l] = imgptr[voffset+l] & m;

        motion_elt_t *vec = motionOut + (i+(mbx+1)*j); 

        if (vec->x == 0 && vec->y == 0) continue;
        if (vec->sad > SAD_LIMIT) continue;

        p = ((vec->x)>>2);
        if(p<0) {a=-1;p=-p;} else a=1;
        if(p>15) p=15;
        q = ((vec->y)>>2);
        if(q<0) {b=-1;q=-q;} else b=1;
        if(q>15) q=15;

        if(p<q) {
          for (int n=0;n<=q;n++) {
            r=mline[n][p]; 
            s=(b*n*width)-(a*r);
            imgptr[k+s]=0;
          }
        } else {
          for (int n=0;n<=p;n++) {
            r=mline[n][q];
            s=(b*r*width)-(a*n);
            imgptr[k+s]=0;
          }
        }
      }
    }
    strOut.write(imageOut);
  }
  return((void *)0);
}
 
/*****************************************************************************/
void cv_init(int w, int h, int f, int fmt)
{
  width=w;height=h;fps=f;

  imageIn.create(width*SCALE, height, CV_8UC1);
  motionIn = new motion_elt_t[((width/16)+1) * (height/16)]; 

  pthread_mutex_init(&imv_mutex, NULL);

  pthread_mutex_init(&img_mutex, NULL);
  pthread_cond_init(&img_condv, NULL);

  pthread_create(&img_thread, NULL, process_thread, (void *)0);

  init_ready=true;
}

/*****************************************************************************/
void cv_process_img(uint8_t *p_buffer, int length, int64_t timestamp)
{
  if (init_ready) {
    pthread_mutex_lock(&img_mutex);
    memcpy(imageIn.data, p_buffer, length);		
    img_ready=true;
    pthread_cond_signal(&img_condv);
    pthread_mutex_unlock(&img_mutex);
  }
}

/*****************************************************************************/
void cv_process_imv(uint8_t *p_buffer, int length, int64_t timestamp)
{
  if (init_ready) {
    pthread_mutex_lock(&imv_mutex);
    memcpy(motionIn ,p_buffer, length);
    imv_ready=true;
    pthread_mutex_unlock(&imv_mutex);
  }
}

/*****************************************************************************/
void cv_close(void)
{
}

cd RaspiCV/src
make

Explorer/RaspberryPi/Visualprocessing/Motionvector/Run