ubuntu V4L2摄像头采集图片 代码

以下是一个简单的示例代码，可以在Ubuntu上使用V4L2接口来捕获摄像头图像并保存为JPEG图片。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <jpeglib.h>

#define VIDEO_DEVICE "/dev/video0"
#define IMAGE_WIDTH 640
#define IMAGE_HEIGHT 480
#define IMAGE_QUALITY 80

int main(int argc, char **argv) {
    int fd = open(VIDEO_DEVICE, O_RDWR);
    if (fd == -1) {
        perror("Failed to open video device");
        return 1;
    }

    struct v4l2_capability cap;
    if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1) {
        perror("Failed to query video device capabilities");
        close(fd);
        return 1;
    }

    struct v4l2_format format;
    format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    format.fmt.pix.width = IMAGE_WIDTH;
    format.fmt.pix.height = IMAGE_HEIGHT;
    format.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
    format.fmt.pix.field = V4L2_FIELD_NONE;
    if (ioctl(fd, VIDIOC_S_FMT, &format) == -1) {
        perror("Failed to set video device format");
        close(fd);
        return 1;
    }

    struct v4l2_requestbuffers reqbuf;
    reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    reqbuf.memory = V4L2_MEMORY_MMAP;
    reqbuf.count = 1;
    if (ioctl(fd, VIDIOC_REQBUFS, &reqbuf) == -1) {
        perror("Failed to request video device buffers");
        close(fd);
        return 1;
    }

    struct v4l2_buffer buffer;
    buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buffer.memory = V4L2_MEMORY_MMAP;
    buffer.index = 0;
    if (ioctl(fd, VIDIOC_QUERYBUF, &buffer) == -1) {
        perror("Failed to query video device buffer");
        close(fd);
        return 1;
    }

    void *mem = mmap(NULL, buffer.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buffer.m.offset);
    if (mem == MAP_FAILED) {
        perror("Failed to map video device buffer");
        close(fd);
        return 1;
    }

    if (ioctl(fd, VIDIOC_STREAMON, &buffer.type) == -1) {
        perror("Failed to start video device stream");
        munmap(mem, buffer.length);
        close(fd);
        return 1;
    }

    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
    unsigned char *jpeg_data;
    unsigned long jpeg_size;
    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_compress(&cinfo);
    jpeg_mem_dest(&cinfo, &jpeg_data, &jpeg_size);
    cinfo.image_width = IMAGE_WIDTH;
    cinfo.image_height = IMAGE_HEIGHT;
    cinfo.input_components = 3;
    cinfo.in_color_space = JCS_RGB;
    jpeg_set_defaults(&cinfo);
    jpeg_set_quality(&cinfo, IMAGE_QUALITY, true);

    if (ioctl(fd, VIDIOC_QBUF, &buffer) == -1) {
        perror("Failed to queue video device buffer");
        munmap(mem, buffer.length);
        close(fd);
        return 1;
    }

    if (ioctl(fd, VIDIOC_DQBUF, &buffer) == -1) {
        perror("Failed to dequeue video device buffer");
        munmap(mem, buffer.length);
        close(fd);
        return 1;
    }

    jpeg_start_compress(&cinfo, true);
    JSAMPROW row_pointer[1];
    for (int y = 0; y < IMAGE_HEIGHT; y++) {
        row_pointer[0] = (JSAMPROW)((unsigned char *)mem + y * buffer.bytesused);
        jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }
    jpeg_finish_compress(&cinfo);

    FILE *fp = fopen("image.jpg", "wb");
    if (fp == NULL) {
        perror("Failed to open image file");
        munmap(mem, buffer.length);
        close(fd);
        return 1;
    }
    fwrite(jpeg_data, jpeg_size, 1, fp);
    fclose(fp);

    jpeg_destroy_compress(&cinfo);
    munmap(mem, buffer.length);
    close(fd);
    return 0;
}

注意：这个示例代码仅仅是一个基础的例子，实际使用时需要考虑更多的情况，例如错误处理、缓冲区管理、图像分辨率、图像格式、图像质量等。此外，还需要安装libjpeg库，否则会编译错误。