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#include <errno.h>
#include <fcntl.h>
#include <linux/videodev2.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
uint8_t *buffer;
static int xioctl(int fd, int request, void *arg)
{
int r;
do r = ioctl (fd, request, arg);
while (-1 == r && EINTR == errno);
return r;
}
int print_caps(int fd)
{
struct v4l2_capability caps = {};
if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &caps))
{
perror("Querying Capabilities");
return 1;
}
printf( "Driver Caps:\n"
" Driver: \"%s\"\n"
" Card: \"%s\"\n"
" Bus: \"%s\"\n"
" Version: %d.%d\n"
" Capabilities: %08x\n",
caps.driver,
caps.card,
caps.bus_info,
(caps.version>>16)&&0xff,
(caps.version>>24)&&0xff,
caps.capabilities);
struct v4l2_cropcap cropcap = {0};
cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == xioctl (fd, VIDIOC_CROPCAP, &cropcap))
{
perror("Querying Cropping Capabilities");
return 1;
}
printf( "Camera Cropping:\n"
" Bounds: %dx%d+%d+%d\n"
" Default: %dx%d+%d+%d\n"
" Aspect: %d/%d\n",
cropcap.bounds.width, cropcap.bounds.height, cropcap.bounds.left, cropcap.bounds.top,
cropcap.defrect.width, cropcap.defrect.height, cropcap.defrect.left, cropcap.defrect.top,
cropcap.pixelaspect.numerator, cropcap.pixelaspect.denominator);
int support_grbg10 = 0;
struct v4l2_fmtdesc fmtdesc = {0};
fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
char fourcc[5] = {0};
char c, e;
printf(" FMT : CE Desc\n--------------------\n");
while (0 == xioctl(fd, VIDIOC_ENUM_FMT, &fmtdesc))
{
strncpy(fourcc, (char *)&fmtdesc.pixelformat, 4);
if (fmtdesc.pixelformat == V4L2_PIX_FMT_SGRBG10)
support_grbg10 = 1;
c = fmtdesc.flags & 1? 'C' : ' ';
e = fmtdesc.flags & 2? 'E' : ' ';
printf(" %s: %c%c %s\n", fourcc, c, e, fmtdesc.description);
fmtdesc.index++;
}
/*
if (!support_grbg10)
{
printf("Doesn't support GRBG10.\n");
return 1;
}*/
struct v4l2_format fmt = {0};
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = 640;
fmt.fmt.pix.height = 480;
//fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_BGR24;
//fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_GREY;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
fmt.fmt.pix.field = V4L2_FIELD_NONE;
if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
{
perror("Setting Pixel Format");
return 1;
}
strncpy(fourcc, (char *)&fmt.fmt.pix.pixelformat, 4);
printf( "Selected Camera Mode:\n"
" Width: %d\n"
" Height: %d\n"
" PixFmt: %s\n"
" Field: %d\n",
fmt.fmt.pix.width,
fmt.fmt.pix.height,
fourcc,
fmt.fmt.pix.field);
return 0;
}
int init_mmap(int fd)
{
struct v4l2_requestbuffers req = {0};
req.count = 1;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req))
{
perror("Requesting Buffer");
return 1;
}
struct v4l2_buffer buf = {0};
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = 0;
if(-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
{
perror("Querying Buffer");
return 1;
}
buffer = mmap (NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
printf("Length: %d\nAddress: %p\n", buf.length, buffer);
printf("Image Length: %d\n", buf.bytesused);
return 0;
}
int capture_image(int fd)
{
struct v4l2_buffer buf = {0};
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = 0;
if(-1 == xioctl(fd, VIDIOC_QBUF, &buf))
{
perror("Query Buffer");
return 1;
}
if(-1 == xioctl(fd, VIDIOC_STREAMON, &buf.type))
{
perror("Start Capture");
return 1;
}
fd_set fds;
FD_ZERO(&fds);
FD_SET(fd, &fds);
struct timeval tv = {0};
tv.tv_sec = 2;
int r = select(fd+1, &fds, NULL, NULL, &tv);
if(-1 == r)
{
perror("Waiting for Frame");
return 1;
}
if(-1 == xioctl(fd, VIDIOC_DQBUF, &buf))
{
perror("Retrieving Frame");
return 1;
}
printf ("saving image\n");
IplImage* frame;
CvMat cvmat = cvMat(480, 640, CV_8UC3, (void*)buffer);
frame = cvDecodeImage(&cvmat, 1);
cvNamedWindow("window",CV_WINDOW_AUTOSIZE);
cvShowImage("window", frame);
cvWaitKey(0);
cvSaveImage("image.jpg", frame, 0);
return 0;
}
int main()
{
int fd;
fd = open("/dev/video0", O_RDWR);
if (fd == -1)
{
perror("Opening video device");
return 1;
}
if(print_caps(fd))
return 1;
if(init_mmap(fd))
return 1;
int i;
for(i=0; i<5; i++)
{
if(capture_image(fd))
return 1;
}
close(fd);
return 0;
}

Hi How to configure this driver for multiple webcameras image capturing?

Thank you so much fir such an awesome explanation on http://www.jayrambhia.com/blog/capture-v4l2/ and this code too... thnx! :D

Do you tested this code in a loop? Test it take more than one frame, put the capture_image function in a for loop with 10 iterations for example. It will produce a kernel panic. Could you fix this? Thanks a lot.

ssaeger commented Jan 4, 2015

@victorsantosdev: I had the same problem and could resolve it.
First, add a flag variable to mark if your camera is active. (e.g. bool camActive = false).
Then I added a check in the capture_image function around the part that starts the capturing, which checks if the camera is active:

...
if (!camActive) {
    if (-1 == xioctl(gVidInt, VIDIOC_STREAMON, &buf.type)) {
        perror("Start Capture");
    }
    FD_ZERO(&fds);
    FD_SET(gVidInt, &fds);
    camActive = true;
}
...

With this code the camera is only activated once when the first image is captured. If you try to activate the camera again when it is already activated you will get a kernel panic.

Hi bro , my laptop integrated webcam is working great the also starts capture by blinking light near my webcam only problem is i am getting an image length as 0 ,what may have gone wrong ?

Thanks

@ghost

ghost commented Feb 7, 2015

First off, thanks for posting on your blog and gist this nice snippet. Exactly what I was looking for!

BUT, it causes kernel panics every time it makes a call to cvSaveImage under capture_image. I was looking for documentation on the last parameter and it seems like it should be optional (OpenCV 2.4.8), but still couldn't compile. I also hear that the C bindings are deprecated, which is too bad. Anyways, I have a fix that hopefully might prevent others from having to reboot (flashing keyboard and everything).

http://stackoverflow.com/questions/801054/opencv-cvsaveimage-jpeg-compression-factor

int p[3];
p[0] = CV_IMWRITE_JPEG_QUALITY;
p[1] = 100;
p[2] = 0;
cvSaveImage("image.jpg", frame, p);

Hi, thank you and congratulations by article, i have the same problem of pankajnsarode, my webcam light turn on, but, i never meet the picture, someone help me please.

The ioctl to invoke VIDIOC_STREAMON is called several times in a loop. Except for the first time, the second call would cause a failure and program returns such that the system is likely to hang.
A alternative fix is to call VIDIOC_STREAMOFF after saving the image.

whscfan commented Apr 15, 2016

Dear Jay Rambhia,
Thanks for your share.I run your code success to store a picture.On other way ,my project aim to record a video ,but it is not work with you code :

CvMat cvmat = cvMat(480, 640, CV_8UC3, (void*)buffer);
IplImage * img;
img = cvDecodeImage(&cvmat, 1);

can you help me to convert the buffer data into Opencv datatype?

Thank you so much!

VeCAD commented Jul 22, 2017 edited

Thank you for this code, among all the V4l2 camera capture C codes out there, this is the most simplest to understand and use. I realized there's some memory leak issues with the original when performing continuous streaming from camera, so I made some changes for future use and reference.

Invoking VIDIOC_STREAMON repeatedly in a loop leads to additional overhead. And we need to release IplImage* frame by using cvReleaseImage(&frame). Listed my changes below. In main code, I just called capture_image(fd) in main without loops.

int capture_image(int fd)
{
struct v4l2_buffer buf = {0};
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = 0;

if(-1 == xioctl(fd, VIDIOC_STREAMON, &buf.type))
{
    perror("Start Capture");
    return 1;
}

IplImage* frame;
CvMat cvmat = cvMat(480, 640, CV_8UC3, (void*)buffer);


while (true) {

if(-1 == xioctl(fd, VIDIOC_QBUF, &buf))
{
    perror("Query Buffer");
    return 1;
}

fd_set fds;
FD_ZERO(&fds);
FD_SET(fd, &fds);
struct timeval tv = {0};
tv.tv_sec = 2;
int r = select(fd+1, &fds, NULL, NULL, &tv);
if(-1 == r)
{
    perror("Waiting for Frame");
    return 1;
}

if(-1 == xioctl(fd, VIDIOC_DQBUF, &buf))
{
    perror("Retrieving Frame");
    return 1;
}
//printf ("saving image\n");

frame = cvDecodeImage(&cvmat, 1);
cvNamedWindow("window",CV_WINDOW_AUTOSIZE);
cvShowImage("window", frame);
//cvWaitKey(0);
//cvSaveImage("image.jpg", frame, 0);
cvReleaseImage(&frame);

if (cvWaitKey(1) >= 0)
break; //enter to stop streaming
}

if(-1 == xioctl(fd, VIDIOC_STREAMOFF, &buf.type))
{
    perror("End Capture");
    return 1;
}

}

Wvisee commented Aug 5, 2017

This is cool ! Thanks a lot :D

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