前言 很多天了,看了数不尽的论坛和各网站的帖子后,我把我遇到的问题都解决的差不多了,感觉应该是把摄像头跑起来了,但还是遇到了一些问题,似乎是图像处理方面的,我好像解决不了这个问题了,我好想有个人帮帮我。写这篇文章估计得花3~4小时,我真心希望哪位朋友能明白我的想法,能顺手帮帮我。 正文 一,我的思路 我想用一幅图来说明我所做的事情,如图1所示(图中uvcdriver标错了,应该是uvcvideo)。 图1 图1左侧是图像采集,右侧是图像显示。采集的帧速是30 帧/秒。 二,v4l2(video for linux two) 驱动摄像头的是uvcdriver,该驱动设计时采用了v4l系列的标准(该标准好像是linuxTV制定的,linuxTV的官网是http:///),我的CentOS6.3(内核是linux-2.6.32.60)采用的是v4l2标准。一开始我编写应用程序的时候什么都不懂,见论坛上帖子怎么讲,我就怎么写,当中很多是参照v4l标准,我当时不知道,直接照抄,出了问题,改用v4l2标准后才解决了问题。v4l2 API的在/usr/include/linux/videodev2.h头文件中,很容易就找到了。 采集图像的实例程序网上很多,但最经典的还是linuxTV官网推出的capture.c,这里给出地址http:///downloads/legacy/video4linux/API/V4L2_API/v4l2spec/capture.c这个程序写的很好,很值得研究。 我就是借鉴的这个程序,然后得到我的摄像头设备的信息,如图2(那个pixel_format应该用十六进制表示的,我没注意,十六进制的话应该是0x56595559,即YUYV的意思)所示。 图2 一插上摄像头,uvcvideo就直接把我的摄像头识别了。 v4l2我不想再多写了,基本上只要看了那个经典的capture.c就够了。 三,framebuffer 就目前我这水平,我还不想涉及到QT或者别的什么面向对象编程,我想简单一点,慢慢来。于是我直接选择了framebuffer,它的API在usr/include/linux/fb.h头文件中。刚开始用open函数打开/dev/fb0的时候根本就打不开,愣是要把grub设置一下,如图3所示。后面显示的时候要切记切换到命令行模式。 图3 关于那个vga=0x311以及一系列的frambuffer编程我是参照http://bbs./thread-2000076-1-1.html这个人的文章的,这里我复制一下他的一张表到下面,如表1所示。 4bit 8bit 15bit 16bit 24bit 32bit 640x400 x 0x300 x x x x 640x480 x 0x301 0x310 0x311 0x312 x 800x600 0x302 0x303 0x313 0x314 0x315 x 1024x768 x 0x305 0x316 0x317 0x318 x 1280x1024 x 0x307 0x319 0x31A 0x31B x 1600x1200 x 0x31C 0x31D 0x31E 0x31F x 表1 因为我采集视频的图像时640*480,然后是16bit的BPP,所以我选择了0x311 framebuffer编程很简单,比v4l2简单多了。我截个图来表达我用framebuffer API得到的我的显示屏的信息,如图4所示。 图4 四,v4l2+framebuffer 我把v4l和framebuffer集成到一块儿了。因为capture.c图像处理部分没有什么内容,所以,图像处理部分是我自己写的。我的摄像头采集的图像的像素编码是YUYV或者说是YUV422格式,每个像素是16bit。我做的事情就是把YUV422_16转换成RGB565_16,采集的图像尺寸是640*480的,显示屏也是640*480。 对于YUV422_16我想具体一点(因为当初觉得YUV格式很抽象,总是搞不懂)。然后看到一个表好像蛮形象的,我先把表画下来,如表2所示 像素:Y0U0V0 Y1U1V1 Y2U2V2 Y3U3V3 ... 采集:Y0U0V0 Y1 Y2U2V2 Y3 ... 存储:Y0U0Y1V0 Y2U2Y3V2 表2 Y0是一个字节,U0也是一个字节,V0也是一个字节,都是一个字节。 客观上每个像素是3个字节,但采集的时候却不是3个字节都采集,这样采集:第0个像素(Y0 U0 V0)采集了3个字节(Y0 U0 V0),第1个像素采集了1个字节(Y1),第2个像素采集了3个字节(Y2 U2 V2),第3个像素采集了1个字节(Y3)……第n个像素采集了3个字节(Yn Un Vn),第n+1个像素采集了1个字节(Yn+1)……。这种采集方式叫相邻两像素共用UV(不知道能不能从数学上证明如果每个像素3个字节都采集的话是不是就是冗余)。 怎么存储呢?好像是间隔存储。我记得好像有宏像素的概念,即2个像素占4个字节或者说4个字节的存储单元保存着2个像素的信息。比如Y0U0V1V0共需要一个字(4个字节),这个字的存储单元里保存着第0个像素和第1个像素的信息,第0个像素和第1个像素共享U0和V0。反正在后面的图像处理当中,我是用一个unsigned long *p的指针来处理一个宏像素的。当然了,这张表看不懂没关系,我当初就没看懂。 然后就是RGB了,我感觉RGB还是蛮形象的,尤其是RGB565_16,网上好多人研究这个,这里我就不多说了。 对于YUV和RGB之间的转换,我理解的程度也不深,我怕我的图像处理问题就是出在这个上面。 五,v4l2+framebuffer的组合效果 我看到我的摄像头采集出来的视频流了,因为担心YUV和RGB之间的转换时的数值处理出问题,我就只取了Y分量,我听说有黑白图像一说(其实YUV分量都提取的话,效果还是一样)。 1,提取YUV2分量代码如下: Y0=(*from & 0x000000FF)>>0; U0=(*from & 0x0000FF00)>>8; //colorful //U0=128; //white and black Y1=(*from & 0x00FF0000)>>16; V0=(*from & 0xFF000000)>>24; //colorful //V0=128; //white and blcak 注:from是unsigned long型的指针变量,指向YUV2缓存。 2,根据提取到的YUV分量,转换成RGB分量函数: static void YUV2RGB(unsigned char Y,unsigned char U,unsigned char V, unsigned char *R,unsigned char *G,unsigned char *B) { /* *R=Y+1.4075*(V-128); *G=Y-0.3455*(U-128)-0.7169*(V-128); *B=Y+1.779*(U-128); *R=Y+1.140*V; *G=Y-0.394*U-0.581*V; *B=Y+2.032*U; */ *R=Y+(V-128)+((V-128)*103>>8); *G=Y-((U-128)*88>>8)-((V-128)*183>>8); *B=Y+(U-128)+((U-128)*198>>8); } 3,把RGB分量再编码成像素:*to = (R0&0x1F)<<11 | (G0&0x3F)<<5 |(B0&0x1F)<<0;*to |= ((R1&0x1F)<<11 | (G1&0x3F)<<5 |(B1&0x1F)<<0)<<16; 注:to是unsigned long型指针变量,指向RGB565输出缓存。 编译好程序后,我用ctrl+alt+F2切换到命令行模式看看效果,我先截图,如图5和图6所示 图5(我的v4l2+framebuffer) 图6(关掉台灯,我的v4l2+framebuffer) 我ctrl+alt+F1切换到图形界面,看看cheese的效果,如图7所示。 图7(cheese) 为什么cheese的效果会这么好(显示效果不流畅,但画面很美),为什么我的视频的图像会成为这个样子(显示效果很流畅,但画面很丑),我搞了好长时间都发现不了问题出在哪里。谁能帮帮我吗? 六,程序 我的程序就一个bluelover.c文件。 /* * This program can be used and distributed without restrictions. */ #include #include #include #include/* low-level i/o */ #include #include #include #include #include #include #include #include #include #include #include #define CLEAR(x) memset(&(x), 0, sizeof(x)) struct buffer { void *start; size_t length; }; static char *dev_name1; static char *dev_name2; static int fd1 = -1; static int fd2 = -1; struct buffer *buffers; static unsigned int n_buffers; static char *fb_buffer; static unsigned long screensize; static char *yuv_buffer; static char *rgb_buffer; static int force_format=false; static int frame_count = 1000; static void errno_exit(const char *s) { fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno)); exit(EXIT_FAILURE); } static int xioctl(int fh, int request, void *arg) { int r; do { r = ioctl(fh, request, arg); } while (-1 == r && EINTR == errno); return r; } /* static void process_image(const void *p, int size) { unsigned short *fb; unsigned short *rgb; unsigned long height = 480; if(size>screensize) size=screensize; //move memcpy(yuv_buffer,p,size); //proc memcpy(rgb_buffer,yuv_buffer,size); //move memcpy(fb_buffer,yuv_buffer,size); //move rgb=(unsigned short*)rgb_buffer; fb=(unsigned short*)fb_buffer; while(height--) { memcpy(fb,rgb,1280); fb+=640; rgb+=640; } fflush(stderr); fprintf(stderr, "."); fflush(stdout); } */ static void YUV2RGB(unsigned char Y,unsigned char U,unsigned char V, unsigned char *R,unsigned char *G,unsigned char *B) /*static void YUV2RGB(int Y,int U,int V, int *R,int *G,int *B)*/ { /* *R=Y+1.4075*(V-128); *G=Y-0.3455*(U-128)-0.7169*(V-128); *B=Y+1.779*(U-128); */ *R=Y+(V-128)+((V-128)*103>>8); *G=Y-((U-128)*88>>8)-((V-128)*183>>8); *B=Y+(U-128)+((U-128)*198>>8); } static void process_image(const unsigned long *from, int size) { unsigned long *to =(unsigned long*)fb_buffer; unsigned char Y0; unsigned char U0; unsigned char Y1; unsigned char V0; unsigned char R0; unsigned char G0; unsigned char B0; unsigned char R1; unsigned char G1; unsigned char B1; size>>=2; while(size--) { Y0=(*from & 0x000000FF)>>0; U0=128; //white and black //U0=(*from & 0x0000FF00)>>8; //colorful Y1=(*from & 0x00FF0000)>>16; V0=128; //white and blcak //V0=(*from & 0xFF000000)>>24; //colorful YUV2RGB(Y0,U0,V0,&R0,&G0,&B0); YUV2RGB(Y1,U0,V0,&R1,&G1,&B1); *to = (R0&0x1F)<<11 | (G0&0x3F)<<5 |(B0&0x1F)<<0; *to |= ((R1&0x1F)<<11 | (G1&0x3F)<<5 |(B1&0x1F)<<0)<<16; from++; to++; } } static int read_frame(void) { struct v4l2_buffer buf; CLEAR(buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; if (-1 == xioctl(fd1, VIDIOC_DQBUF, &buf)) { switch (errno) { case EAGAIN: return 0; case EIO: default: errno_exit("VIDIOC_DQBUF"); } } assert(buf.index < n_buffers); process_image(buffers[buf.index].start, buf.bytesused); if (-1 == xioctl(fd1, VIDIOC_QBUF, &buf)) errno_exit("VIDIOC_QBUF"); return 1; } static void mainloop(void) { unsigned int count; count = frame_count; while (count-- > 0) { for (;;) { fd_set fds; struct timeval tv; int r; FD_ZERO(&fds); FD_SET(fd1, &fds); /* Timeout. */ tv.tv_sec = 2; tv.tv_usec = 0; r = select(fd1 + 1, &fds, NULL, NULL, &tv); if (-1 == r) { if (EINTR == errno) continue; errno_exit("select"); } if (0 == r) { fprintf(stderr, "select timeout\n"); exit(EXIT_FAILURE); } if (read_frame()) break; /* EAGAIN - continue select loop. */ } } } static void stop_capturing(void) { enum v4l2_buf_type type; type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == xioctl(fd1, VIDIOC_STREAMOFF, &type)) errno_exit("VIDIOC_STREAMOFF"); } static void start_capturing(void) { unsigned int i; enum v4l2_buf_type type; struct v4l2_buffer buf; for (i = 0; i < n_buffers; ++i) { CLEAR(buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = i; if (-1 == xioctl(fd1, VIDIOC_QBUF, &buf)) errno_exit("VIDIOC_QBUF"); } type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == xioctl(fd1, VIDIOC_STREAMON, &type)) errno_exit("VIDIOC_STREAMON"); } static void uninit_device(void) { unsigned int i; for (i = 0; i < n_buffers; ++i) if (-1 == munmap(buffers[i].start, buffers[i].length)) errno_exit("munmap"); if(-1 == munmap(fb_buffer,screensize)) errno_exit("munmap"); free(buffers); free(rgb_buffer); free(yuv_buffer); } static void init_mmap(void) { struct v4l2_requestbuffers req; struct v4l2_buffer buf; //VIDIOC_REQBUFS CLEAR(req); req.count = 4; req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; req.memory = V4L2_MEMORY_MMAP; if(-1 == xioctl(fd1, VIDIOC_REQBUFS, &req)) { if (EINVAL == errno) { fprintf(stderr, "%s does not support ""memory mapping\n", dev_name1); exit(EXIT_FAILURE); } else errno_exit("VIDIOC_REQBUFS"); } if(req.count < 2) { fprintf(stderr, "Insufficient buffer memory on %s\n",dev_name1); exit(EXIT_FAILURE); } //VIDIOC_QUERYBUF buffers = calloc(req.count, sizeof(*buffers)); if (!buffers) { fprintf(stderr, "Out of memory\n"); exit(EXIT_FAILURE); } for (n_buffers = 0; n_buffers < req.count; ++n_buffers) { CLEAR(buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = n_buffers; if (-1 == xioctl(fd1, VIDIOC_QUERYBUF, &buf)) errno_exit("VIDIOC_QUERYBUF"); buffers[n_buffers].length = buf.length; buffers[n_buffers].start =mmap(NULL /* start anywhere */,buf.length, PROT_READ | PROT_WRITE /* required */, MAP_SHARED /* recommended */, fd1, buf.m.offset); if (MAP_FAILED == buffers[n_buffers].start) { errno_exit("mmap"); } }//now n_buffers is 4 //fbmmap fb_buffer=(char*)mmap(NULL,screensize,PROT_READ | PROT_WRITE,MAP_SHARED,fd2,0); if(MAP_FAILED == fb_buffer) { errno_exit("mmap"); } //malloc the yuv_buffer yuv_buffer = (char*)malloc(screensize); if (!yuv_buffer) { fprintf(stderr, "Out of memory\n"); exit(EXIT_FAILURE); } //malloc the rgb_buffer rgb_buffer = (char*)malloc(screensize); if (!rgb_buffer) { fprintf(stderr, "Out of memory\n"); exit(EXIT_FAILURE); } } static void init_device(void) { struct v4l2_capability cap; struct v4l2_format fmt; struct fb_fix_screeninfo finfo; struct fb_var_screeninfo vinfo; CLEAR(cap); if (-1 == xioctl(fd1, VIDIOC_QUERYCAP, &cap)) { if (EINVAL == errno) { fprintf(stderr, "%s is no V4L2 device\n",dev_name1); exit(EXIT_FAILURE); } else errno_exit("VIDIOC_QUERYCAP"); } if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) { fprintf(stderr, "%s is no video capture device\n",dev_name1); exit(EXIT_FAILURE); } if (!(cap.capabilities & V4L2_CAP_STREAMING)) { fprintf(stderr, "%s does not support streaming i/o\n",dev_name1); exit(EXIT_FAILURE); } CLEAR(fmt); fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (force_format) { fmt.fmt.pix.width = 640; fmt.fmt.pix.height = 480; fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV; fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; if (-1 == xioctl(fd1, VIDIOC_S_FMT, &fmt)) errno_exit("VIDIOC_S_FMT"); } else { if (-1 == xioctl(fd1, VIDIOC_G_FMT, &fmt)) errno_exit("VIDIOC_G_FMT"); } fprintf(stdout,"<------------camera infomation------------->\n"); fprintf(stdout,"device driver=%s\n",cap.driver); fprintf(stdout,"device name=%s\n",cap.card); fprintf(stdout,"bus_infomation=%s\n",cap.bus_info); fprintf(stdout,"image_width=%d\n",fmt.fmt.pix.width); fprintf(stdout,"image_height=%d\n",fmt.fmt.pix.height); fprintf(stdout,"pixel_format=%d\n",fmt.fmt.pix.pixelformat); fprintf(stdout,"\n"); CLEAR(finfo); if(-1 == xioctl(fd2,FBIOGET_FSCREENINFO,&finfo)) errno_exit("FBIOGET_FSCREENINFO"); CLEAR(vinfo); if(-1 == xioctl(fd2,FBIOGET_VSCREENINFO,&vinfo)) errno_exit("FBIOGET_VSCREENINFO"); screensize = vinfo.xres*vinfo.yres*vinfo.bits_per_pixel/8; fprintf(stdout,"<------------screen infomation------------->\n"); fprintf(stdout,"id=%s\n",finfo.id); fprintf(stdout,"x=%d\n",vinfo.xres); fprintf(stdout,"y=%d\n",vinfo.yres); fprintf(stdout,"bpp=%d\n",vinfo.bits_per_pixel); fprintf(stdout,"redoffset=%d,redlength=%d,msb_right=%d\n", vinfo.red.offset,vinfo.red.length,vinfo.red.msb_right); fprintf(stdout,"greenoffset=%d,greenlength=%d,msb_right=%d\n", vinfo.green.offset,vinfo.green.length,vinfo.green.msb_right); fprintf(stdout,"blueoffset=%d,bluelength=%d,msb_right=%d\n", vinfo.blue.offset,vinfo.blue.length,vinfo.blue.msb_right); fprintf(stdout,"screensize=%d\n",screensize); init_mmap(); } static void close_device(void) { if (-1 == close(fd1)) errno_exit("close"); fd1 = -1; if (-1 == close(fd2)) errno_exit("close"); fd2 = -1; } static void open_device(void) { fd1 = open(dev_name1, O_RDWR /* required */ | O_NONBLOCK, 0); if (-1 == fd1) { fprintf(stderr, "Cannot open '%s': %d, %s\n",dev_name1, errno, strerror(errno)); exit(EXIT_FAILURE); } fd2 = open(dev_name2,O_RDWR,0); if(-1 == fd2) { fprintf(stderr, "Cannot open '%s': %d, %s\n",dev_name2, errno, strerror(errno)); exit(EXIT_FAILURE); } } int main(int argc, char **argv) { dev_name1 = "/dev/video0"; dev_name2 = "/dev/fb0"; open_device(); init_device(); start_capturing(); mainloop(); stop_capturing(); uninit_device(); close_device(); fprintf(stderr, "\n"); return 0; } 后记 等解决了这个问题再写吧。 |
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