ARMLinuxLCD上实时预览摄像头画面

文章目录 1、前言2、环境介绍3、步骤4、应用程序编写4.1、lcd初始化4.2、摄像头初始化4.3、jpeg解码4.4、开启摄像头4.5、完整的程序如下 5、测试5.1、编译应用程序5.2、运行应用程序 6、总结

1、前言

本次应用程序主要针对支持MJPEG格式输出的UVC摄像头。

2、环境介绍

rk3566 + 7寸 mipi lcd + uvc摄像头

3、步骤

应用程序编写主要分为以下几个步骤：

1、lcd初始化。

2、摄像头初始化。

3、摄像头采集数据。

4、jpeg解码。

5、lcd显示。

4、应用程序编写 4.1、lcd初始化 typedef struct lcd_mes { int fd; unsigned char *fb_base; int lcd_width; int lcd_height; unsigned int bpp; unsigned int line_width; } lcd_mes; int lcd_init(const char *fb_dev, lcd_mes *lcd) { int screen_size; struct fb_var_screeninfo var; if (fb_dev == NULL) goto _err; /* 1. open /dev/fb* */ lcd->fd = open(fb_dev, O_RDWR); if(lcd->fd < 0) { printf("can not open %s\n", fb_dev); goto _err; } /* 2. get lcd message */ if (ioctl(lcd->fd, FBIOGET_VSCREENINFO, &var)) { printf("can not get var\n"); goto _err; } screen_size = var.xres * var.yres * var.bits_per_pixel / 8; lcd->line_width = var.xres * var.bits_per_pixel / 8; lcd->lcd_width = var.xres; lcd->lcd_height = var.yres; lcd->bpp = var.bits_per_pixel; lcd->fb_base = mmap(NULL, screen_size, PROT_READ | PROT_WRITE, MAP_SHARED, lcd->fd, 0); if (lcd->fb_base == (unsigned char *)-1) { printf("can not mmap\n"); goto _err; } memset(lcd->fb_base, 0x00, screen_size); return 0; _err: return -1; } 4.2、摄像头初始化

使用v4l2接口初始化uvc摄像头：

typedef struct camera_mes { int fd; void *bufs[32]; int bufs_index; int buf_length; char fmt[20]; int frame_x_size; int frame_y_size; } camera_mes; int camera_init(const char *video, camera_mes *camera) { struct v4l2_fmtdesc fmtdesc; struct v4l2_frmsizeenum fsenum; int fmt_index = 0; int frame_index = 0; int buf_cnt; int i; if (video == NULL) goto _err; /* 1. open /dev/video* */ camera->fd = open(video, O_RDWR); if (camera->fd < 0) { printf("can not open %s\n", video); goto _err; } /* 2. query capability */ struct v4l2_capability cap; memset(&cap, 0, sizeof(struct v4l2_capability)); if (0 == ioctl(camera->fd, VIDIOC_QUERYCAP, &cap)) { if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == 0) { fprintf(stderr, "Error opening device %s: video capture not supported.\n", video); goto _ioc_querycap_err; } if(!(cap.capabilities & V4L2_CAP_STREAMING)) { fprintf(stderr, "%s does not support streaming i/o\n", video); goto _ioc_querycap_err; } } else { printf("can not get capability\n"); goto _ioc_querycap_err; } /* 3. enum formt */ while (1) { fmtdesc.index = fmt_index; fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (0 != ioctl(camera->fd, VIDIOC_ENUM_FMT, &fmtdesc)) break; frame_index = 0; // printf("format %s,%d:\n", fmtdesc.description, fmtdesc.pixelformat); while (1) { memset(&fsenum, 0, sizeof(struct v4l2_frmsizeenum)); fsenum.pixel_format = fmtdesc.pixelformat; fsenum.index = frame_index; /* get framesize */ if (ioctl(camera->fd, VIDIOC_ENUM_FRAMESIZES, &fsenum) == 0) { // printf("\t%d: %d x %d\n", frame_index, fsenum.discrete.width, fsenum.discrete.height); } else { break; } frame_index++; } fmt_index++; } /* 4. set formt */ struct v4l2_format fmt; memset(&fmt, 0, sizeof(struct v4l2_format)); fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; fmt.fmt.pix.width = camera->frame_x_size; fmt.fmt.pix.height = camera->frame_y_size; fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG; fmt.fmt.pix.field = V4L2_FIELD_ANY; if (0 == ioctl(camera->fd, VIDIOC_S_FMT, &fmt)) { // printf("the final frame-size has been set : %d x %d\n", fmt.fmt.pix.width, fmt.fmt.pix.height); camera->frame_x_size = fmt.fmt.pix.width; camera->frame_y_size = fmt.fmt.pix.height; strncpy(camera->fmt, "Motion-JPEG", strlen("Motion-JPEG")); } else { printf("can not set format\n"); goto _ioc_sfmt_err; } /* 5. require buffer */ struct v4l2_requestbuffers rb; memset(&rb, 0, sizeof(struct v4l2_requestbuffers)); rb.count = 32; rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; rb.memory = V4L2_MEMORY_MMAP; if (0 == ioctl(camera->fd, VIDIOC_REQBUFS, &rb)) { buf_cnt = rb.count; for(i = 0; i < rb.count; i++) { struct v4l2_buffer buf; memset(&buf, 0, sizeof(struct v4l2_buffer)); buf.index = i; buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if (0 == ioctl(camera->fd, VIDIOC_QUERYBUF, &buf)) { /* mmap */ camera->bufs[i] = mmap(0, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, camera->fd, buf.m.offset); if(camera->bufs[i] == MAP_FAILED) { printf("Unable to map buffer"); goto _err; } } else { printf("can not query buffer\n"); goto _err; } } } else { printf("can not request buffers\n"); goto _ioc_reqbufs_err; } /* 6. queue buffer */ for(i = 0; i < buf_cnt; ++i) { struct v4l2_buffer buf; memset(&buf, 0, sizeof(struct v4l2_buffer)); buf.index = i; buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if (0 != ioctl(camera->fd, VIDIOC_QBUF, &buf)) { perror("Unable to queue buffer"); goto _ioc_qbuf_err; } } camera->bufs_index = 0; // init camera struct camera->buf_length = 0; return 0; _ioc_qbuf_err: _ioc_reqbufs_err: _ioc_sfmt_err: _ioc_querycap_err: _err: return -1; } 4.3、jpeg解码 int jpeg_show_on_lcd(lcd_mes *lcd, camera_mes *camera) { int min_width, min_height; int valid_bytes; int offset_x, offset_y; struct jpeg_decompress_struct cinfo; struct jpeg_error_mgr jerr; cinfo.err = jpeg_std_error(&jerr); // 错误处理对象与解码对象绑定 jpeg_create_decompress(&cinfo); // 初始化解码器 jpeg_mem_src(&cinfo, camera->bufs[camera->bufs_index], camera->buf_length); // 指定JPEG数据的来源 jpeg_read_header(&cinfo, TRUE); // 读取图像信息 cinfo.out_color_space = JCS_RGB; // 设置解码后的颜色空间为RGB jpeg_start_decompress(&cinfo); // 开始解码 unsigned char *jpeg_line_buf = (char *)malloc(cinfo.output_components * cinfo.output_width); // 用于存储从JPEG解码器读取的一行数据 unsigned int *fb_line_buf = (int *)malloc(lcd->line_width); // 用于存储转换后的RGB数据，准备写入framebuffer min_width = (cinfo.output_width < lcd->lcd_width) ? cinfo.output_width : lcd->lcd_width; min_height = (cinfo.output_height < lcd->lcd_height) ? cinfo.output_height : lcd->lcd_height; valid_bytes = min_width * lcd->bpp / 8; // 一行的有效字节数 unsigned char *ptr = lcd->fb_base; offset_x = ((lcd->lcd_width - min_width) / 2) * lcd->bpp / 8; // x方向居中 offset_y = (lcd->lcd_height - min_height) / 2; // y方向居中 for (int i = 0; i < offset_y; i++) ptr += lcd->lcd_width * lcd->bpp / 8; unsigned int red, green, blue; unsigned int color; while (cinfo.output_scanline < min_height) { jpeg_read_scanlines(&cinfo, &jpeg_line_buf, 1); // 每次读取一行 for(int i = 0; i < min_width; i++) { red = jpeg_line_buf[i * 3]; green = jpeg_line_buf[i * 3 + 1]; blue = jpeg_line_buf[i * 3 + 2]; color = red << 16 | green << 8 | blue; // RGB888转RGB8888 fb_line_buf[i] = color; } memcpy(ptr + offset_x, fb_line_buf, valid_bytes); // 将一行数据写入framebuffer ptr += lcd->lcd_width * lcd->bpp / 8; // 移动到下一行 } jpeg_finish_decompress(&cinfo); // 完成解码 jpeg_destroy_decompress(&cinfo); // 销毁解码对象 free(jpeg_line_buf); // 释放内存 free(fb_line_buf); // 释放内存 return 0; } 4.4、开启摄像头 int main(int argc, char **argv) { ... /* start camera */ if (0 != ioctl(camera.fd, VIDIOC_STREAMON, &type)) { printf("Unable to start capture\n"); goto _err; } printf("\nstart camera ...\n"); while (1) { /* poll */ memset(fds, 0, sizeof(fds)); fds[0].fd = camera.fd; fds[0].events = POLLIN; if (1 == poll(fds, 1, -1)) { /* dequeue buffer */ struct v4l2_buffer buf; memset(&buf, 0, sizeof(struct v4l2_buffer)); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if (0 != ioctl(camera.fd, VIDIOC_DQBUF, &buf)) { printf("Unable to dequeue buffer\n"); goto _ioc_dqbuf_err; } /* jpeg show on lcd */ camera.bufs_index = buf.index; camera.buf_length = buf.length; jpeg_show_on_lcd(&lcd, &camera); /* queue buffer */ if (0 != ioctl(camera.fd, VIDIOC_QBUF, &buf)) { printf("Unable to queue buffer"); goto _ioc_qbuf_err; } } } ... } 4.5、完整的程序如下 #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <sys/ioctl.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <linux/types.h> #include <linux/videodev2.h> #include <poll.h> #include <sys/mman.h> #include <jpeglib.h> #include <linux/fb.h> typedef struct lcd_mes { int fd; unsigned char *fb_base; int lcd_width; int lcd_height; unsigned int bpp; unsigned int line_width; } lcd_mes; typedef struct camera_mes { int fd; void *bufs[32]; int bufs_index; int buf_length; char fmt[20]; int frame_x_size; int frame_y_size; } camera_mes; int jpeg_show_on_lcd(lcd_mes *lcd, camera_mes *camera) { int min_width, min_height; int valid_bytes; int offset_x, offset_y; struct jpeg_decompress_struct cinfo; struct jpeg_error_mgr jerr; cinfo.err = jpeg_std_error(&jerr); // 错误处理对象与解码对象绑定 jpeg_create_decompress(&cinfo); // 初始化解码器 jpeg_mem_src(&cinfo, camera->bufs[camera->bufs_index], camera->buf_length); // 指定JPEG数据的来源 jpeg_read_header(&cinfo, TRUE); // 读取图像信息 cinfo.out_color_space = JCS_RGB; // 设置解码后的颜色空间为RGB jpeg_start_decompress(&cinfo); // 开始解码 unsigned char *jpeg_line_buf = (char *)malloc(cinfo.output_components * cinfo.output_width); // 用于存储从JPEG解码器读取的一行数据 unsigned int *fb_line_buf = (int *)malloc(lcd->line_width); // 用于存储转换后的RGB数据，准备写入framebuffer min_width = (cinfo.output_width < lcd->lcd_width) ? cinfo.output_width : lcd->lcd_width; min_height = (cinfo.output_height < lcd->lcd_height) ? cinfo.output_height : lcd->lcd_height; valid_bytes = min_width * lcd->bpp / 8; // 一行的有效字节数 unsigned char *ptr = lcd->fb_base; offset_x = ((lcd->lcd_width - min_width) / 2) * lcd->bpp / 8; // x方向居中 offset_y = (lcd->lcd_height - min_height) / 2; // y方向居中 for (int i = 0; i < offset_y; i++) ptr += lcd->lcd_width * lcd->bpp / 8; unsigned int red, green, blue; unsigned int color; while (cinfo.output_scanline < min_height) { jpeg_read_scanlines(&cinfo, &jpeg_line_buf, 1); // 每次读取一行 for(int i = 0; i < min_width; i++) { red = jpeg_line_buf[i * 3]; green = jpeg_line_buf[i * 3 + 1]; blue = jpeg_line_buf[i * 3 + 2]; color = red << 16 | green << 8 | blue; // RGB888转RGB8888 fb_line_buf[i] = color; } memcpy(ptr + offset_x, fb_line_buf, valid_bytes); // 将一行数据写入framebuffer ptr += lcd->lcd_width * lcd->bpp / 8; // 移动到下一行 } jpeg_finish_decompress(&cinfo); // 完成解码 jpeg_destroy_decompress(&cinfo); // 销毁解码对象 free(jpeg_line_buf); // 释放内存 free(fb_line_buf); // 释放内存 return 0; } int lcd_init(const char *fb_dev, lcd_mes *lcd) { int screen_size; struct fb_var_screeninfo var; if (fb_dev == NULL) goto _err; /* 1. open /dev/fb* */ lcd->fd = open(fb_dev, O_RDWR); if(lcd->fd < 0) { printf("can not open %s\n", fb_dev); goto _err; } /* 2. get lcd message */ if (ioctl(lcd->fd, FBIOGET_VSCREENINFO, &var)) { printf("can not get var\n"); goto _err; } screen_size = var.xres * var.yres * var.bits_per_pixel / 8; lcd->line_width = var.xres * var.bits_per_pixel / 8; lcd->lcd_width = var.xres; lcd->lcd_height = var.yres; lcd->bpp = var.bits_per_pixel; lcd->fb_base = mmap(NULL, screen_size, PROT_READ | PROT_WRITE, MAP_SHARED, lcd->fd, 0); if (lcd->fb_base == (unsigned char *)-1) { printf("can not mmap\n"); goto _err; } memset(lcd->fb_base, 0x00, screen_size); return 0; _err: return -1; } int camera_init(const char *video, camera_mes *camera) { struct v4l2_fmtdesc fmtdesc; struct v4l2_frmsizeenum fsenum; int fmt_index = 0; int frame_index = 0; int buf_cnt; int i; if (video == NULL) goto _err; /* 1. open /dev/video* */ camera->fd = open(video, O_RDWR); if (camera->fd < 0) { printf("can not open %s\n", video); goto _err; } /* 2. query capability */ struct v4l2_capability cap; memset(&cap, 0, sizeof(struct v4l2_capability)); if (0 == ioctl(camera->fd, VIDIOC_QUERYCAP, &cap)) { if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == 0) { fprintf(stderr, "Error opening device %s: video capture not supported.\n", video); goto _ioc_querycap_err; } if(!(cap.capabilities & V4L2_CAP_STREAMING)) { fprintf(stderr, "%s does not support streaming i/o\n", video); goto _ioc_querycap_err; } } else { printf("can not get capability\n"); goto _ioc_querycap_err; } /* 3. enum formt */ while (1) { fmtdesc.index = fmt_index; fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (0 != ioctl(camera->fd, VIDIOC_ENUM_FMT, &fmtdesc)) break; frame_index = 0; // printf("format %s,%d:\n", fmtdesc.description, fmtdesc.pixelformat); while (1) { memset(&fsenum, 0, sizeof(struct v4l2_frmsizeenum)); fsenum.pixel_format = fmtdesc.pixelformat; fsenum.index = frame_index; /* get framesize */ if (ioctl(camera->fd, VIDIOC_ENUM_FRAMESIZES, &fsenum) == 0) { // printf("\t%d: %d x %d\n", frame_index, fsenum.discrete.width, fsenum.discrete.height); } else { break; } frame_index++; } fmt_index++; } /* 4. set formt */ struct v4l2_format fmt; memset(&fmt, 0, sizeof(struct v4l2_format)); fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; fmt.fmt.pix.width = camera->frame_x_size; fmt.fmt.pix.height = camera->frame_y_size; fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG; fmt.fmt.pix.field = V4L2_FIELD_ANY; if (0 == ioctl(camera->fd, VIDIOC_S_FMT, &fmt)) { // printf("the final frame-size has been set : %d x %d\n", fmt.fmt.pix.width, fmt.fmt.pix.height); camera->frame_x_size = fmt.fmt.pix.width; camera->frame_y_size = fmt.fmt.pix.height; strncpy(camera->fmt, "Motion-JPEG", strlen("Motion-JPEG")); } else { printf("can not set format\n"); goto _ioc_sfmt_err; } /* 5. require buffer */ struct v4l2_requestbuffers rb; memset(&rb, 0, sizeof(struct v4l2_requestbuffers)); rb.count = 32; rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; rb.memory = V4L2_MEMORY_MMAP; if (0 == ioctl(camera->fd, VIDIOC_REQBUFS, &rb)) { buf_cnt = rb.count; for(i = 0; i < rb.count; i++) { struct v4l2_buffer buf; memset(&buf, 0, sizeof(struct v4l2_buffer)); buf.index = i; buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if (0 == ioctl(camera->fd, VIDIOC_QUERYBUF, &buf)) { /* mmap */ camera->bufs[i] = mmap(0, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, camera->fd, buf.m.offset); if(camera->bufs[i] == MAP_FAILED) { printf("Unable to map buffer"); goto _err; } } else { printf("can not query buffer\n"); goto _err; } } } else { printf("can not request buffers\n"); goto _ioc_reqbufs_err; } /* 6. queue buffer */ for(i = 0; i < buf_cnt; ++i) { struct v4l2_buffer buf; memset(&buf, 0, sizeof(struct v4l2_buffer)); buf.index = i; buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if (0 != ioctl(camera->fd, VIDIOC_QBUF, &buf)) { perror("Unable to queue buffer"); goto _ioc_qbuf_err; } } camera->bufs_index = 0; // init camera struct camera->buf_length = 0; return 0; _ioc_qbuf_err: _ioc_reqbufs_err: _ioc_sfmt_err: _ioc_querycap_err: _err: return -1; } int main(int argc, char **argv) { int ret; lcd_mes lcd; camera_mes camera; int type = V4L2_BUF_TYPE_VIDEO_CAPTURE; struct pollfd fds[1]; if (argc != 3) { printf("Usage: %s </dev/videoX> </dev/fbX>\n", argv[0]); return -1; } /* lcd init */ ret = lcd_init(argv[2], &lcd); if (ret == -1) { printf("lcd init err !\n"); goto _err; } printf("\n-------------- lcd message --------------\n"); printf("screen pixel: %d x %d\n", lcd.lcd_width, lcd.lcd_height); printf("line width: %d (byte)\n", lcd.line_width); printf("bpp: %d\n", lcd.bpp); printf("-----------------------------------------\n"); /* camera init */ camera.frame_x_size = lcd.lcd_width; camera.frame_y_size = lcd.lcd_height; ret = camera_init(argv[1], &camera); if (ret == -1) { printf("camera init err !\n"); goto _err; } printf("\n------------ camera message -------------\n"); printf("frame size: %d x %d\n", camera.frame_x_size, camera.frame_y_size); printf("format: %s\n", camera.fmt); printf("-----------------------------------------\n"); /* start camera */ if (0 != ioctl(camera.fd, VIDIOC_STREAMON, &type)) { printf("Unable to start capture\n"); goto _err; } printf("\nstart camera ...\n"); while (1) { /* poll */ memset(fds, 0, sizeof(fds)); fds[0].fd = camera.fd; fds[0].events = POLLIN; if (1 == poll(fds, 1, -1)) { /* dequeue buffer */ struct v4l2_buffer buf; memset(&buf, 0, sizeof(struct v4l2_buffer)); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if (0 != ioctl(camera.fd, VIDIOC_DQBUF, &buf)) { printf("Unable to dequeue buffer\n"); goto _ioc_dqbuf_err; } /* jpeg show on lcd */ camera.bufs_index = buf.index; camera.buf_length = buf.length; jpeg_show_on_lcd(&lcd, &camera); /* queue buffer */ if (0 != ioctl(camera.fd, VIDIOC_QBUF, &buf)) { printf("Unable to queue buffer"); goto _ioc_qbuf_err; } } } /* close camera */ if (0 != ioctl(camera.fd, VIDIOC_STREAMOFF, &type)) { printf("Unable to stop capture\n"); goto _ioc_streamoff_err; } close(camera.fd); return 0; _ioc_streamoff_err: _ioc_qbuf_err: _ioc_dqbuf_err: _err: return -1; } 5、测试 5.1、编译应用程序

如果你使用的buildroot系统，需要交叉编译。

这里测试所使用的板子跑的是ubuntu，执行如下命令直接编译：

sudo gcc -o uvctolcd uvctolcd.c -ljpeg 5.2、运行应用程序 sudo ./uvctolcd /dev/video10 /dev/fb0

6、总结

参考文章：Linux摄像头（v4l2应用）——在LCD上实时显示摄像头采集JPEG数据_v4l2调用并显示图像-CSDN博客