Explorer/RaspberryPi/Visualprocessing/Motionvector
Jump to navigation
Jump to search
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 2000
#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 Mat1b gray;
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);
Mat3b grayBGR;
Mat colormap;
int32_t sum_x,sum_y;
int mbx = width/16;
int mby = height/16;
int mbxy = (8 * mbx * mby);
unsigned int motionSize = ((mbx+1)*mby) * sizeof(struct motion_elt_t);
motion_elt_t *motionOut = new motion_elt_t[(mbx+1)*mby];
char buff[20];int lg;
while (true) {
pthread_mutex_lock(&img_mutex);
while (!img_ready) pthread_cond_wait(&img_condv, &img_mutex);
cvtColor(gray, grayBGR, COLOR_GRAY2BGR);
applyColorMap(grayBGR, colormap, COLORMAP_JET);
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);
}
sum_x=0;sum_y=0;
for (int j=0;j<mby;j++) {
for (int i=0;i<mbx;i++) {
motion_elt_t *vec = motionOut + (i+(mbx+1)*j);
if (vec->x == 0 && vec->y == 0) continue;
if (vec->sad > SAD_LIMIT) continue;
int x = i*16 + 8;
int y = j*16 + 8;
float intensity = vec->sad;
intensity = round(255 * intensity / SAD_LIMIT);
if (intensity > 255) intensity = 255;
uint8_t *ptr = colormap.ptr<uchar>(0);
uint8_t idx = 3*(uint8_t)intensity;
arrowedLine(grayBGR, Point(x+vec->x, y+vec->y),
Point(x, y),
Scalar(ptr[idx], ptr[idx+1], ptr[idx+2]));
sum_x += (intensity * vec->x);
sum_y += (intensity * vec->y);
}
}
sum_x = (sum_x/mbxy);
sum_y = (sum_y/mbxy);
arrowedLine(grayBGR, Point(320,240),Point(320+sum_x,240+sum_y),Scalar(0,255,0),5);
drawAxes(&grayBGR);
strOut.write(grayBGR);
}
return((void *)0);
}
/*****************************************************************************/
void cv_init(int w, int h, int f, int fmt)
{
// freopen( "/tmp/error.txt", "w", stderr );
// cerr << length << endl;
// fd << static_cast<int32_t>(sum_x) << endl;
drawAxes_init();
width=w;height=h;fps=f;
gray = Mat(height, width, 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(gray.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