Explorer/RaspberryPi/Visualprocessing/Motionvector
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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 compiled as "raspicv", with a custom "cv.cpp" (see below), output motion vector display to /tmp/camera3
The "cv.cpp" is limited to 640x480 grayscale image in this sample.
(ref. 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