这几天在做小车的过程中，需要用到图像采集。我想现在用的摄像头是UVC免驱的。根据国嵌的教程中有一个gspca摄像头的程序。我发现把gspca的采集程序用到uvc上时，在显示图像的时候提示没有huffman表。但是在显示gspca的摄像头时却没有问题。为此特别找了以下的程序来获取uvc摄像头的数据。
程序代码:
/** capturing from UVC cam* requires: libjpeg-dev* build: gcc -std=c99 capture.c -ljpeg -o capture*/#include <stdint.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <errno.h>#include <fcntl.h>#include <sys/ioctl.h>#include <sys/mman.h>#include <asm/types.h>#include <linux/videodev2.h>#include <sys/time.h>#include <sys/types.h>#include <unistd.h>#include <jpeglib.h>void quit(const char * msg){fprintf(stderr, "[%s] %d: %s\n", msg, errno, strerror(errno));exit(EXIT_FAILURE);}int xioctl(int fd, int request, void* arg){for (int i = 0; i < 100; i++) {int r = ioctl(fd, request, arg);if (r != -1 || errno != EINTR) return r;}return -1;}typedef struct {uint8_t* start;size_t length;} buffer_t;typedef struct {int fd;uint32_t width;uint32_t height;size_t buffer_count;buffer_t* buffers;buffer_t head;} camera_t;camera_t* camera_open(const char * device, uint32_t width, uint32_t height){int fd = open(device, O_RDWR | O_NONBLOCK, 0);if (fd == -1) quit("open");camera_t* camera = malloc(sizeof (camera_t));camera->fd = fd;camera->width = width;camera->height = height;camera->buffer_count = 0;camera->buffers = NULL;camera->head.length = 0;camera->head.start = NULL;return camera;}void camera_init(camera_t* camera) {struct v4l2_capability cap;if (xioctl(camera->fd, VIDIOC_QUERYCAP, &cap) == -1) quit("VIDIOC_QUERYCAP");if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) quit("no capture");if (!(cap.capabilities & V4L2_CAP_STREAMING)) quit("no streaming");struct v4l2_cropcap cropcap;memset(&cropcap, 0, sizeof cropcap);cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (xioctl(camera->fd, VIDIOC_CROPCAP, &cropcap) == 0) {struct v4l2_crop crop;crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;crop.c = cropcap.defrect;if (xioctl(camera->fd, VIDIOC_S_CROP, &crop) == -1) {// cropping not supported }}struct v4l2_format format;memset(&format, 0, sizeof format);format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;format.fmt.pix.width = camera->width;format.fmt.pix.height = camera->height;format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;format.fmt.pix.field = V4L2_FIELD_NONE;if (xioctl(camera->fd, VIDIOC_S_FMT, &format) == -1) quit("VIDIOC_S_FMT");struct v4l2_requestbuffers req;memset(&req, 0, sizeof req);req.count = 4;req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;req.memory = V4L2_MEMORY_MMAP;if (xioctl(camera->fd, VIDIOC_REQBUFS, &req) == -1) quit("VIDIOC_REQBUFS");camera->buffer_count = req.count;camera->buffers = calloc(req.count, sizeof (buffer_t));size_t buf_max = 0;for (size_t i = 0; i < camera->buffer_count; i++) {struct v4l2_buffer buf;memset(&buf, 0, sizeof buf);buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = i;if (xioctl(camera->fd, VIDIOC_QUERYBUF, &buf) == -1)quit("VIDIOC_QUERYBUF");if (buf.length > buf_max) buf_max = buf.length;camera->buffers[i].length = buf.length;camera->buffers[i].start =mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED,camera->fd, buf.m.offset);if (camera->buffers[i].start == MAP_FAILED) quit("mmap");}camera->head.start = malloc(buf_max);}void camera_start(camera_t* camera){for (size_t i = 0; i < camera->buffer_count; i++) {struct v4l2_buffer buf;memset(&buf, 0, sizeof buf);buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = i;if (xioctl(camera->fd, VIDIOC_QBUF, &buf) == -1) quit("VIDIOC_QBUF");}enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (xioctl(camera->fd, VIDIOC_STREAMON, &type) == -1)quit("VIDIOC_STREAMON");}void camera_stop(camera_t* camera){enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if (xioctl(camera->fd, VIDIOC_STREAMOFF, &type) == -1)quit("VIDIOC_STREAMOFF");}void camera_finish(camera_t* camera){for (size_t i = 0; i < camera->buffer_count; i++) {munmap(camera->buffers[i].start, camera->buffers[i].length);}free(camera->buffers);camera->buffer_count = 0;camera->buffers = NULL;free(camera->head.start);camera->head.length = 0;camera->head.start = NULL;}void camera_close(camera_t* camera){if (close(camera->fd) == -1) quit("close");free(camera);}int camera_capture(camera_t* camera){struct v4l2_buffer buf;memset(&buf, 0, sizeof buf);buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;if (xioctl(camera->fd, VIDIOC_DQBUF, &buf) == -1) return FALSE;memcpy(camera->head.start, camera->buffers[buf.index].start, buf.bytesused);camera->head.length = buf.bytesused;if (xioctl(camera->fd, VIDIOC_QBUF, &buf) == -1) return FALSE;return TRUE;}int camera_frame(camera_t* camera, struct timeval timeout) {fd_set fds;FD_ZERO(&fds);FD_SET(camera->fd, &fds);int r = select(camera->fd + 1, &fds, 0, 0, &timeout);if (r == -1) quit("select");if (r == 0) return FALSE;return camera_capture(camera);}void jpeg(FILE* dest, uint8_t* rgb, uint32_t width, uint32_t height, int quality){JSAMPARRAY image;image = calloc(height, sizeof (JSAMPROW));for (size_t i = 0; i < height; i++) {image[i] = calloc(width * 3, sizeof (JSAMPLE));for (size_t j = 0; j < width; j++) {image[i][j * 3 + 0] = rgb[(i * width + j) * 3 + 0];image[i][j * 3 + 1] = rgb[(i * width + j) * 3 + 1];image[i][j * 3 + 2] = rgb[(i * width + j) * 3 + 2];}}struct jpeg_compress_struct compress;struct jpeg_error_mgr error;compress.err = jpeg_std_error(&error);jpeg_create_compress(&compress);jpeg_stdio_dest(&compress, dest);compress.image_width = width;compress.image_height = height;compress.input_components = 3;compress.in_color_space = JCS_RGB;jpeg_set_defaults(&compress);jpeg_set_quality(&compress, quality, TRUE);jpeg_start_compress(&compress, TRUE);jpeg_write_scanlines(&compress, image, height);jpeg_finish_compress(&compress);jpeg_destroy_compress(&compress);for (size_t i = 0; i < height; i++) {free(image[i]);}free(image);}int minmax(int min, int v, int max){return (v < min) ? min : (max < v) ? max : v;}uint8_t* yuyv2rgb(uint8_t* yuyv, uint32_t width, uint32_t height){uint8_t* rgb = calloc(width * height * 3, sizeof (uint8_t));for (size_t i = 0; i < height; i++) {for (size_t j = 0; j < width; j += 2) {size_t index = i * width + j;int y0 = yuyv[index * 2 + 0] << 8;int u = yuyv[index * 2 + 1] - 128;int y1 = yuyv[index * 2 + 2] << 8;int v = yuyv[index * 2 + 3] - 128;rgb[index * 3 + 0] = minmax(0, (y0 + 359 * v) >> 8, 255);rgb[index * 3 + 1] = minmax(0, (y0 + 88 * v - 183 * u) >> 8, 255);rgb[index * 3 + 2] = minmax(0, (y0 + 454 * u) >> 8, 255);rgb[index * 3 + 3] = minmax(0, (y1 + 359 * v) >> 8, 255);rgb[index * 3 + 4] = minmax(0, (y1 + 88 * v - 183 * u) >> 8, 255);rgb[index * 3 + 5] = minmax(0, (y1 + 454 * u) >> 8, 255);}}return rgb;}int main(){camera_t* camera = camera_open("/dev/video0", 352, 288);camera_init(camera);camera_start(camera);struct timeval timeout;timeout.tv_sec = 1;timeout.tv_usec = 0;/* skip 5 frames for booting a cam */for (int i = 0; i < 5; i++) {camera_frame(camera, timeout);}camera_frame(camera, timeout);unsigned char* rgb =yuyv2rgb(camera->head.start, camera->width, camera->height);FILE* out = fopen("result.jpg", "w");jpeg(out, rgb, camera->width, camera->height, 100);fclose(out);free(rgb);camera_stop(camera);camera_finish(camera);camera_close(camera);return 0;}
