转自：http://blog.csdn.net/morixinguan/article/details/51001713
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目录(?)[-]
采集方式
V4L2操作流程点击这个网址说得很详细了这里不多说
httpbaikebaiducomview5494174htm
我们都知道，想要驱动Linux下的摄像头，其实很简单，照着V4L2的手册一步步来写，很快就可以写出来，但是在写之前我们要注意改变系统的一些配置，使系统支持framebuffer，在dev下产生fb0这样的节点，这样我们才能在linux系统上操作Camera摄像头,framebuffer在之前的博文已经有说过了，这里就不再提了。
有需要了解framebuffer的那么请点击:http://baike.baidu.com/view/3351639.htm
最重要的，我们需要改一个脚本，在/dev/grub.conf，我们来看看怎么改:
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# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
# all kernel and initrd paths are relative to /boot/, eg.
# root (hd0,0)
# kernel /vmlinuz-version ro root=/dev/sdb2
# initrd /initrd-[generic-]version.img
#boot=/dev/sdb
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.32-431.el6.i686)
root (hd0,0)
kernel /vmlinuz-2.6.32-431.el6.i686 ro root=UUID=2bc12537-d6c1-4e67-b4e5-e9c466205554 nomodeset rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=us rd_NO_MD crashkernel=auto LANG=zh_CN.UTF-8 rd_NO_LVM rd_NO_DM rhgb quiet vga=0x318
initrd /initramfs-2.6.32-431.el6.i686.img
通常情况下，要让framebuffer生效，要加一句vga=???(这里是参数)，简单介绍一下:
我写vga=0x318就是默认就设置为1024x768x24bpp模式。当然还有其它的模式:如下图，根据自己的系统来配置。
色彩 640x400 640x480 800x600 1024x768 1280x1024 1600x1200
4bits ? ? 0x302 ? ? ?
8bits 0x300 0x301 0x303 0x305 0x307 0x31C
15bits ? 0x310 0x313 0x316 0x319 0x31D
16bits ? 0x311 0x314 0x317 0x31A 0x31E
24bits ? 0x312 0x315 0x318 0x31B 0x31F
32bits ? ? ? ? ? ?
配置完成以后，我们先来了解一下V4L2的主要功能。
V4L2就使程序有发现设备和操作设备的能力.它主要是用一系列的回调函数来实现这些功能。像设置摄像头的频率、帧频、视频压缩格式和图像参数等等。当然也可以用于其他多媒体的开发，如音频等。
但是此框架只能运行在Linux操作系统之上。v4L2是针对uvc免驱usb设备的编程框架 ，主要用于采集usb摄像头等，编程模式如下：
采集方式
打开视频设备后，可以设置该视频设备的属性，例如裁剪、缩放等。这一步是可选的。在Linux编程中，一般使用ioctl函数来对设备的I/O通道进行管理：
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extern int ioctl (int __fd, unsigned long int __request, …) __THROW;
__fd：设备的ID，例如刚才用open函数打开视频通道后返回的cameraFd；
__request：具体的命令标志符。
在进行V4L2开发中，一般会用到以下的命令标志符：
VIDIOC_REQBUFS：分配内存
VIDIOC_QUERYBUF：把VIDIOC_REQBUFS中分配的数据缓存转换成物理地址
VIDIOC_QUERYCAP：查询驱动功能
VIDIOC_ENUM_FMT：获取当前驱动支持的视频格式
VIDIOC_S_FMT：设置当前驱动的频捕获格式
VIDIOC_G_FMT：读取当前驱动的频捕获格式
VIDIOC_TRY_FMT：验证当前驱动的显示格式
VIDIOC_CROPCAP：查询驱动的修剪能力
VIDIOC_S_CROP：设置视频信号的边框
VIDIOC_G_CROP：读取视频信号的边框
VIDIOC_QBUF：把数据放回缓存队列
VIDIOC_DQBUF：把数据从缓存中读取出来
VIDIOC_STREAMON：开始视频显示函数
VIDIOC_STREAMOFF：结束视频显示函数
VIDIOC_QUERYSTD：检查当前视频设备支持的标准，例如PAL或NTSC。
这些IO调用，有些是必须的，有些是可选择的。
V4L2操作流程:点击这个网址，说得很详细了，这里不多说。
http://baike.baidu.com/view/5494174.htm
接下来我们来看看实战部分,下面是我自己写的程序接口,可以实现视频采集:生气
1、project.c
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#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include "j-yuv.h"
#include "CameralOpt.h"
#include "FrameBufferOpt.h"
#define WIDTH 640
#define HIGHT 480
int main(void)
{
char yuyv[WIDTH*HIGHT*2];
char bmp[WIDTH*HIGHT*3];
// set_bmp_header((struct bmp_header_t *)bmp, WIDTH, HIGHT);
//初始化摄像头
Init_Cameral(WIDTH , HIGHT );
//初始化framebuffer
Init_FrameBuffer(WIDTH , HIGHT );
//开启摄像头
Start_Cameral();
//采集一张图片
int count = 0 ;
while(1)
{
Get_Picture(yuyv);
yuyv2rgb24(yuyv, bmp, WIDTH, HIGHT);
Write_FrameBuffer(bmp);
// printf("count:%d \n" , count++);
}
//关闭摄像头
Stop_Cameral();
//关闭Framebuffer
Exit_Framebuffer();
//退出
Exit_Cameral();
return 0;
}
2、juv.h
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#ifndef __JYUV_H
#define __JYUV_H
typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned int u32;
#pragma pack(1)
//定义bmp头
struct bmp_header_t{
u16 magic;
u32 file_size;
u32 RESERVED1;
u32 offset; //54 bytes 表示54个偏移量
u32 head_num; //40
u32 width;
u32 height;
u16 color_planes; //1
u16 bit_count;
u32 bit_compression; //0
u32 image_size; //except the size of header
u32 h_resolution;
u32 v_resolution;
u32 color_num;
u32 important_colors;
};
#pragma pack()
void set_bmp_header(struct bmp_header_t * header, u32 width, u32 height);
int yuyv2rgb24(u8 *yuyv, u8 *rgb, u32 width, u32 height);
#endif /* __JYUV_H */
3、juv.c
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#include "j-yuv.h"
#define BIT_COUNT 24
void set_bmp_header(struct bmp_header_t *header, u32 width, u32 height)
{
header->magic = 0x4d42;
header->image_size = width * height * BIT_COUNT/8;
header->file_size = header->image_size + 54;
header->RESERVED1 = 0;
header->offset = 54;
header->head_num = 40;
header->width = width;
header->height = height;
header->color_planes = 1;
header->bit_count = BIT_COUNT;
header->bit_compression = 0;
header->h_resolution = 0;
header->v_resolution = 0;
header->color_num = 0;
header->important_colors = 0;
}
//yuyv转rgb24的算法实现
int yuyv2rgb24(u8 *yuyv, u8 *rgb, u32 width, u32 height)
{
u32 i, in, rgb_index = 0;
u8 y0, u0, y1, v1;
int r, g, b;
u32 out = 0, x, y;
for(in = 0; in < width * height * 2; in += 4)
{
y0 = yuyv[in+0];
u0 = yuyv[in+1];
y1 = yuyv[in+2];
v1 = yuyv[in+3];
for (i = 0; i < 2; i++)
{
if (i)
y = y1;
else
y = y0;
r = y + (140 * (v1-128))/100; //r
g = y - (34 * (u0-128))/100 - (71 * (v1-128))/100; //g
b = y + (177 * (u0-128))/100; //b
if(r > 255) r = 255;
if(g > 255) g = 255;
if(b > 255) b = 255;
if(r < 0) r = 0;
if(g < 0) g = 0;
if(b < 0) b = 0;
y = height - rgb_index/width -1;
x = rgb_index%width;
rgb[(y*width+x)*3+0] = b;
rgb[(y*width+x)*3+1] = g;
rgb[(y*width+x)*3+2] = r;
rgb_index++;
}
}
return 0;
}
4、FrameBufferOpt.c
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#include "FrameBufferOpt.h"
static int Frame_fd ;
static int *FrameBuffer = NULL ;
static int W , H ;
//初始化framebuffer
int Init_FrameBuffer(int Width , int Higth)
{
W = Width ;
H = Higth ;
Frame_fd = open("/dev/fb" , O_RDWR);
if(-1 == Frame_fd)
{
perror("open frame buffer fail");
return -1 ;
}
//根本就不用CPU搬运 用DMA做为搬运工
FrameBuffer = mmap(0, 1280*1024*4 , PROT_READ | PROT_WRITE , MAP_SHARED , Frame_fd ,0 );
if(FrameBuffer == (void *)-1)
{
perror("memory map fail");
return -2 ;
}
return 0 ;
}
//写入framebuffer
int Write_FrameBuffer(const char *buffer)
{
int row , col ;
char *p = NULL ;
for(row = 0 ; row <1024 ; row++)
{
for(col = 0 ; col < 1280 ; col++)
{
if((row < H) && (col < W))
{
p = (char *)(buffer + (row * W+ col ) * 3);
FrameBuffer[row*1280+col] = RGB((unsigned char)(*(p+2)),(unsigned char)(*(p+1)),(unsigned char )(*p));
}
}
}
return 0 ;
}
//退出framebuffer
int Exit_Framebuffer(void)
{
munmap(FrameBuffer , W*H*4);
close(Frame_fd);
return 0 ;
}
5、FrameBufferOpt.h
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#ifndef _FRAMEBUFFEROPT_H
#define _FRAMEBUFFEROPT_H
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#define RGB(r,g,b) ((r<<16)|(g<<8)|b)
//初始化ramebuffer
int Init_FrameBuffer(int Width , int Higth);
//写数据到framebuffer
int Write_FrameBuffer(const char *buffer);
//退出framebuffer
int Exit_Framebuffer(void);
#endif //_FRAMEBUFFEROPT_H
6、CameralOpt.h
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#ifndef _CAMERALOPT_H
#define _CAMERALOPT_H
#include <stdio.h>
#include <linux/videodev2.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/mman.h>
#define COUNT 3
//初始化摄像头
int Init_Cameral(int Width , int Hight);
int Exit_Cameral(void); //退出摄像头
//摄像头开始采集
int Start_Cameral(void);
int Stop_Cameral(void);//停止摄像头
//获取摄像头的数据
int Get_Picture(char *buffer);
#endif //_CAMERALOPT_H
7、CameralOpt.c
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#include "CameralOpt.h"
int video_fd ;
int length ;
char *yuv[COUNT] ;
struct v4l2_buffer enqueue , dequeue ; //定义出入队的操作结构体成员
int Init_Cameral(int Width , int Hight)
{
//参数检查
char *videodevname = NULL ;
videodevname = "/dev/video0" ;
//打开设备
video_fd = open(videodevname , O_RDWR);
if(-1 == video_fd )
{
perror("open video device fail");
return -1 ;
}
int i ;
int ret ;
struct v4l2_format format ;
format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ;
format.fmt.pix.width = Width;
format.fmt.pix.height = Hight;
format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV ; //我支持的格式是这个
ret = ioctl(video_fd , VIDIOC_S_FMT , &format);
if(ret != 0)
{
perror("set video format fail");
return -2 ;
}
//申请buffer,切割成几个部分
//3
struct v4l2_requestbuffers requestbuffer ;
requestbuffer.count = COUNT ;
requestbuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ;
requestbuffer.memory = V4L2_MEMORY_MMAP ;
ret = ioctl(video_fd , VIDIOC_REQBUFS , &requestbuffer);
if(ret != 0)
{
perror("request buffer fail ");
return -3 ;
}
//querybuffer
struct v4l2_buffer querybuffer ;
querybuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ;
querybuffer.memory = V4L2_MEMORY_MMAP ;
for(i = 0 ; i < COUNT ; i++)
{
querybuffer.index = i ;
ret = ioctl(video_fd , VIDIOC_QUERYBUF , &querybuffer);
if(ret != 0)
{
perror("query buffer fail");
return -4 ;
}
// printf("index:%d length:%d offset:%d \n" ,
// querybuffer.index , querybuffer.length , querybuffer.m.offset);
length = querybuffer.length ;
//将摄像头内存印射到进程的内存地址
yuv[i] = mmap(0,querybuffer.length , PROT_READ | PROT_WRITE , MAP_SHARED , video_fd , querybuffer.m.offset );
//列队
struct v4l2_buffer queuebuffer ;
queuebuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ;
queuebuffer.memory = V4L2_MEMORY_MMAP ;
queuebuffer.index = i ;
ret = ioctl(video_fd , VIDIOC_QBUF , &queuebuffer);
if(ret != 0)
{
perror("queuebuffer fail");
return -5 ;
}
}
//初始化入队出队
enqueue.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ;
dequeue.type = V4L2_BUF_TYPE_VIDEO_CAPTURE ;
enqueue.memory = V4L2_MEMORY_MMAP ;
dequeue.memory = V4L2_MEMORY_MMAP ;
return 0 ;
}
int Exit_Cameral(void)
{
int i ;
for(i = 0 ; i < COUNT ; i++)
munmap(yuv+i , length);
close(video_fd);
return 0 ;
}
int Start_Cameral(void)
{
//开启摄像头
int ret ;
int on = 1 ;
ret = ioctl(video_fd , VIDIOC_STREAMON , &on);
if(ret != 0)
{
perror("start Cameral fail");
return -1 ;
}
return 0 ;
}
int Stop_Cameral(void)
{
//停止摄像头
int ret ;
int off= 1 ;
ret = ioctl(video_fd , VIDIOC_STREAMOFF, &off);
if(ret != 0)
{
perror("stop Cameral fail");
return -1 ;
}
return 0 ;
}
int Get_Picture(char *buffer)
{
int ret ;
//出队
ret = ioctl(video_fd , VIDIOC_DQBUF , &dequeue);
if(ret != 0)
{
perror("dequeue fail");
return -1 ;
}
//获取图片数据 YUV yuv[dequeue.index]
memcpy(buffer , yuv[dequeue.index] , dequeue.length);
// write(yuyv_fd , yuv[dequeue.index] , dequeue.length);
enqueue.index = dequeue.index ;
ret = ioctl(video_fd , VIDIOC_QBUF , &enqueue);
if(ret != 0)
{
perror("enqueue fail");
return -2 ;
}
return 0 ;
}
时间： 2024-10-09 09:06:48