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#1 2020-02-05 18:16:54

Jmhh247
会员
注册时间: 2018-12-21
累计积分: 205

[正点原子i.MX6UL] v4l2+framebuffer预览USB摄像头(一):采集拍照

关键字: 正点原子,i.MX6UL,v4l2, framebuffer


- 主机环境:ubuntu16.04-64bit
- 硬件版本:正点原子i.MX6UL emmc

固件帖在本站:[[正点原子i.MX6UL开发板] 编译uboot、linux、buildroot-rootfs](https://whycan.cn/t_3550.html)

---

### 开篇
2020年,注定是不平凡的一年,就当是纸老虎吧。
我遇到的第一个纸老虎是v4l2。
不能出门,就想着玩下USB摄像头,想实现的功能是在LCD屏上实时预览USB摄像头的画面。
搜资料,知道要用v4l2来驱动USB摄像头,第一个难点就是“v4l2”怎么读都不顺。。。
最终,跳过这个难点,确定了使用v4l2+framebuffer预览USB摄像头画面。
参考把“大象放进冰箱”,我决定把实现分成三步,以降低难度、建立信心。

本篇主要实现采集拍照。

### 正题

#### 一、相关概念
概念尽量简短不占篇幅,主要记录实践的过程。

- USB摄像头用的是UVC(USB Video Class)标准类,免驱。
- v4l2(Video for linux2)是linux提供的视频设备编程API。
- USB摄像头一般都支持输出YUV数据。
- YUV是一种颜色空间,通常需要转成RGB使用(bmp保存或LCD显示,等)。
- YUYV是YUV的一种,也叫YUV422。
- BMP图是RGB数据,上下颠倒存放的。

#### 二、操作分解
v4l2驱动USB摄像头的采集流程还是容易看明白,大致是:打开摄像头设置参数,申请设置缓冲区,然后从缓冲区每次读一帧即可。

##### s0.核心指令
v4l2 主要通过调用 ioctl 配合一系列 VIDIOC_XXXXXX 指令完成,很友好。

#include <sys/ioctl.h>
#include <linux/videodev2.h>

##### s1.打开摄像头
俗话说,一切皆文件。

#include <fcntl.h>

fd = open("/dev/videox", O_RDWR);

##### s2.获取属性

ioctl(fd, VIDIOC_QUERYCAP, &cap);

##### s3.设置参数
输出格式、分辨率、帧率等。

ioctl(fd, VIDIOC_S_FMT, &fmt);
ioctl(fd, VIDIOC_S_PARM, &setfps);

##### s4.设置缓冲区
- 简单理解就是配置FIFO(先进先出环形队列)。
- 映射到用户空间。
- 核心操作围绕struct v4l2_buffer结构体的index成员变量。

struct v4l2_buffer buf;

// 出队
ioctl(fd, VIDIOC_DQBUF, &buf);

// 入队
ioctl(fd, VIDIOC_QBUF, &buf);

##### s5.采集控制

int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

// 启动采集
ioctl (fd, VIDIOC_STREAMON, &type);

// 停止采集
ioctl (fd, VIDIOC_STREAMOFF, &type);

##### s6.采集一帧

ioctl(fd, VIDIOC_DQBUF, &buf);

##### s7.视频处理
转换成RGB,然后保存成BMP图片实现拍照。


#### 三、代码实现

主要参考了开源项目MJPG-streamer的v4l2采集代码,完全手打。

- 代码1

本代码主要实现了获取USB相机的信息,相当于v4l2版的"hello world"。

/*
 * @FilePath: /v4l2-fb-uvc-code/v4l2grap-uvc-getinfo.c
 * @Version: 1.0.0
 * @Author: zys
 * @LastAuthor   : zys
 * @CreationDate: 2020-02-04 11:33:25
 * @LastEditTime : 2020-02-05 17:57:18
 * @Description :  获取USB相机的信息,相当于v4l2版的"hello world"。
 */


/*----------------------------------------------------------------------------*/
/* change log ----------------------------------------------------------------*/
/*
    
    -0205
     获取USB相机信息 ok.
*/



/*----------------------------------------------------------------------------*/
/* Includes ------------------------------------------------------------------*/
#include <fcntl.h>
#include <linux/videodev2.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

/* Private define ------------------------------------------------------------*/
#define _UVC_CAM_HEIGHT (680)
#define _UVC_CAM_WIDTH  (480)
/* Private macro -------------------------------------------------------------*/
/* Private typedef -----------------------------------------------------------*/
struct vdIn {
    int   fd;
    char* videodevice;

    // v4l2
    struct v4l2_capability     cap;
    struct v4l2_format         fmt;
    struct v4l2_fmtdesc        fmtdesc;
    struct v4l2_streamparm     setfps;
    struct v4l2_requestbuffers rb;

    int width;
    int height;
    int fps;
};

/* Private function prototypes -----------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
static struct vdIn uvc_cam;

/* Global  variables ---------------------------------------------------------*/
/* Private functions ---------------------------------------------------------*/



int v4l2_init(void)
{
    int ret;


    // 1. open cam
    if ((uvc_cam.fd = open(uvc_cam.videodevice, O_RDWR)) == -1) {
        printf("ERROR opening V4L interface\n");
        return -1;
    }

    // 2. querycap
    memset(&uvc_cam.cap, 0, sizeof(struct v4l2_capability));
    ret = ioctl(uvc_cam.fd, VIDIOC_QUERYCAP, &uvc_cam.cap);

    if (ret < 0) {
        printf("Error opening device %s: unable to query device.\n", uvc_cam.videodevice);
        return -1;
    }
    else {
        printf("driver:\t\t%s\n", uvc_cam.cap.driver);
        printf("card:\t\t%s\n", uvc_cam.cap.card);
        printf("bus_info:\t%s\n", uvc_cam.cap.bus_info);
        printf("version:\t%d\n", uvc_cam.cap.version);
        printf("capabilities:\t%x\n", uvc_cam.cap.capabilities);

        if ((uvc_cam.cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE) {
            printf("%s: \tsupports capture.\n", uvc_cam.videodevice);
        }

        if ((uvc_cam.cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING) {
            printf("%s: \tsupports streaming.\n", uvc_cam.videodevice);
        }
    }

    // 3. set format in

    // 3.1 enum fmt
    printf("\nSupport format:\n");

    memset(&uvc_cam.fmtdesc, 0, sizeof(struct v4l2_fmtdesc));
    uvc_cam.fmtdesc.index = 0;
    uvc_cam.fmtdesc.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    while (ioctl(uvc_cam.fd, VIDIOC_ENUM_FMT, &uvc_cam.fmtdesc) != -1) {
        printf("\t%d.%s\n", uvc_cam.fmtdesc.index + 1, uvc_cam.fmtdesc.description);
        uvc_cam.fmtdesc.index++;
    }

    // 3.2 set fmt
    memset(&uvc_cam.fmt, 0, sizeof(struct v4l2_format));
    uvc_cam.fmt.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    uvc_cam.fmt.fmt.pix.width       = uvc_cam.width;
    uvc_cam.fmt.fmt.pix.height      = uvc_cam.height;
    uvc_cam.fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    uvc_cam.fmt.fmt.pix.field       = V4L2_FIELD_ANY;

    ret = ioctl(uvc_cam.fd, VIDIOC_S_FMT, &uvc_cam.fmt);
    if (ret < 0) {
        printf("Unable to set format\n");
        return -1;
    }

    // 3.3 get fmt
    ret = ioctl(uvc_cam.fd, VIDIOC_G_FMT, &uvc_cam.fmt);
    if (ret < 0) {
        printf("Unable to get format\n");
        return -1;
    }
    else {
        printf("\nfmt.type:\t\t%d\n", uvc_cam.fmt.type);
        printf("pix.pixelformat:\t%c%c%c%c\n", uvc_cam.fmt.fmt.pix.pixelformat & 0xFF, (uvc_cam.fmt.fmt.pix.pixelformat >> 8) & 0xFF, (uvc_cam.fmt.fmt.pix.pixelformat >> 16) & 0xFF, (uvc_cam.fmt.fmt.pix.pixelformat >> 24) & 0xFF);
        printf("pix.height:\t\t%d\n", uvc_cam.fmt.fmt.pix.height);
        printf("pix.width:\t\t%d\n", uvc_cam.fmt.fmt.pix.width);
        printf("pix.field:\t\t%d\n", uvc_cam.fmt.fmt.pix.field);
    }


    // 4. set fps
    memset(&uvc_cam.setfps, 0, sizeof(struct v4l2_streamparm));
    uvc_cam.setfps.type                                  = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    uvc_cam.setfps.parm.capture.timeperframe.numerator   = 1;
    uvc_cam.setfps.parm.capture.timeperframe.denominator = 25;

    ret = ioctl(uvc_cam.fd, VIDIOC_S_PARM, &uvc_cam.setfps);

    if (ret < 0) {
        printf("Unable to set frame rate\n");
        return -1;
    }
    else {
        printf("set fps OK!\n");
    }

    ret = ioctl(uvc_cam.fd, VIDIOC_G_PARM, &uvc_cam.setfps);

    if (ret < 0) {
        printf("Unable to get frame rate\n");
        return -1;
    }
    else {
        printf("get fps OK:\n");
        printf("timeperframe.numerator  : %d\n", uvc_cam.setfps.parm.capture.timeperframe.numerator);
        printf("timeperframe.denominator: %d\n", uvc_cam.setfps.parm.capture.timeperframe.denominator);
        printf("set fps : %d\n", 1 * uvc_cam.setfps.parm.capture.timeperframe.denominator / uvc_cam.setfps.parm.capture.timeperframe.numerator);
    }

    // 5. enum framesizes
    int i = 0;

    while (1) {
        struct v4l2_fmtdesc fmtdesc;
        memset(&fmtdesc, 0, sizeof(struct v4l2_fmtdesc));
        fmtdesc.index = i++;
        fmtdesc.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE;

        if (ioctl(uvc_cam.fd, VIDIOC_ENUM_FMT, &fmtdesc) < 0) {
            break;
        }

        printf("Supported format: %s\n", fmtdesc.description);
        struct v4l2_frmsizeenum fsenum;
        memset(&fsenum, 0, sizeof(struct v4l2_frmsizeenum));
        fsenum.pixel_format = uvc_cam.fmtdesc.pixelformat;

        int j = 0;

        while (1) {
            fsenum.index = j;
            j++;

            if (ioctl(uvc_cam.fd, VIDIOC_ENUM_FRAMESIZES, &fsenum) == 0) {
                if (uvc_cam.fmt.fmt.pix.pixelformat == fmtdesc.pixelformat) {
                    printf("\tSupported size with the current format: %dx%d\n", fsenum.discrete.width, fsenum.discrete.height);
                }
                else {
                    printf("\tSupported size: %dx%d\n", fsenum.discrete.width, fsenum.discrete.height);
                }
            }
            else {
                break;
            }
        }
    }


    printf("init %s \t[OK]\n", uvc_cam.videodevice);

    return 0;
}

void v4l2_exit(void)
{
    close(uvc_cam.fd);
}


int main(int argc, char const* argv[])
{
    char vdname[15];

    printf("\n----- v4l2 app start ----- \n");

    if (argc < 2) {

        printf("need:/dev/videox\n");
        printf("like:./av4l2grap-uvc-x /dev/video1\n");
        printf("app exit.\n\n");
        exit(1);
    }

    snprintf(vdname, 12, argv[1]);

    memset(&uvc_cam, 0, sizeof(struct vdIn));
    uvc_cam.videodevice = vdname;
    printf("using: \t\t%s\n", uvc_cam.videodevice);


    uvc_cam.width  = _UVC_CAM_WIDTH;
    uvc_cam.height = _UVC_CAM_HEIGHT;

    if (v4l2_init() < 0) {
        goto app_exit;
    }

app_exit:
    printf("app exit.\n\n");
    v4l2_exit();

    return 0;
}





/*************************** (C) COPYRIGHT 2020 ZYS ************END OF FILE****/

- 代码2

拍照代码还未实现,后续会更新上~

#### 四、测试程序

- 编译程序

arm-buildroot-linux-gnueabihf-gcc -o av4l2grap-uvc-getinfo-x v4l2grap-uvc-getinfo.c

- 确认开发板的USB相机设备号

重要:记得插上USB相机!

# ls /dev/video*
/dev/video0  /dev/video1  /dev/video2
# cat /sys/class/video4linux/video1/name
Aoni HD Camera
#

- 运行程序

先把程序复制到开发板,推荐用NFS。

运行程序:

# ./av4l2grap-uvc-getinfo-x /dev/video1

----- v4l2 app start -----
using:          /dev/video1
driver:         uvcvideo
card:           Aoni HD Camera
bus_info:       usb-ci_hdrc.1-1.4
version:        262415
capabilities:   84200001
/dev/video1:    supports capture.
/dev/video1:    supports streaming.

Support format:
        1.MJPEG
        2.YUV 4:2:2 (YUYV)

fmt.type:               1
pix.pixelformat:        YUYV
pix.height:             480
pix.width:              640
pix.field:              1
set fps OK!
get fps OK:
timeperframe.numerator  : 1
timeperframe.denominator: 25
set fps : 25
Supported format: MJPEG
        Supported size: 640x480
        Supported size: 1280x720
        Supported size: 1184x656
        Supported size: 1024x576
        Supported size: 960x720
        Supported size: 960x540
        Supported size: 864x486
        Supported size: 800x600
        Supported size: 752x423
        Supported size: 640x360
        Supported size: 320x240
Supported format: YUV 4:2:2 (YUYV)
        Supported size with the current format: 640x480
        Supported size with the current format: 1280x720
        Supported size with the current format: 1184x656
        Supported size with the current format: 1024x576
        Supported size with the current format: 960x720
        Supported size with the current format: 960x540
        Supported size with the current format: 864x486
        Supported size with the current format: 800x600
        Supported size with the current format: 752x423
        Supported size with the current format: 640x360
        Supported size with the current format: 320x240
init /dev/video1        [OK]
app exit.

#

离线

#2 2020-02-05 18:17:30

Jmhh247
会员
注册时间: 2018-12-21
累计积分: 205

Re: [正点原子i.MX6UL] v4l2+framebuffer预览USB摄像头(一):采集拍照

占楼

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#3 2020-02-05 18:18:09

Jmhh247
会员
注册时间: 2018-12-21
累计积分: 205

Re: [正点原子i.MX6UL] v4l2+framebuffer预览USB摄像头(一):采集拍照

占楼

离线

#4 2020-02-05 18:20:31

cityf
会员
注册时间: 2017-11-03
累计积分: 195

Re: [正点原子i.MX6UL] v4l2+framebuffer预览USB摄像头(一):采集拍照

楼主的文档和代码一样优秀!

离线

#5 2020-02-07 12:07:42

Jmhh247
会员
注册时间: 2018-12-21
累计积分: 205

Re: [正点原子i.MX6UL] v4l2+framebuffer预览USB摄像头(一):采集拍照

#### 拍照代码测试Ok

0207
---
#### 代码2 实现拍照功能

运行程序后会在当前目录生成uvc_grap.bmp。可以复制到ubuntu查看图片。

- 知识点

主要是自己的理解。

1.yuyv与rgb888:

yuyv原始数据里,两个像素点共用了uv分量,两个像素占用4个字节;
rgb888大家应该都知道了,一个像素点占用3个字节,那么两个像素点占用6个字节。
由此可知,yuyv与rgb888字节量比列是 4:6,也就是 2:3。

知道这些就可以定义相关数据缓冲区大小了:

// buf for yuyv
uvc_cam.framesizeIn = uvc_cam.width * uvc_cam.height << 1; // w * h * 2
uvc_cam.framebuffer = (unsigned char*)calloc(1, (size_t)uvc_cam.framesizeIn);

// buf for rgb888
static unsigned char rgb888_buffer[IMAGEWIDTH * IMAGEHEIGHT * 3];

2.bmp:

基础的图片格式网上很多介绍,不再说明,核心关注点是——数据上下颠倒存放的


- 实现源码:

/*
 * @FilePath: /v4l2-fb-uvc-code/v4l2grap-uvc-savebmp.c
 * @Version: 1.0.0
 * @Author: zys
 * @LastAuthor   : zys
 * @CreationDate: 2020-02-04 11:33:25
 * @LastEditTime : 2020-02-07 11:08:21
 * @Description :  采集一帧USB摄像头数据,保存成bmp图片。
 */


/*----------------------------------------------------------------------------*/
/* change log ----------------------------------------------------------------*/
/*
    
    -0205
     获取USB相机信息 ok.

    -0207
     实现拍照功能:运行程序后会在当前目录生成uvc_grap.bmp。可以复制到ubuntu查看图片。
*/



/*----------------------------------------------------------------------------*/
/* Includes ------------------------------------------------------------------*/
#include <fcntl.h>
#include <linux/videodev2.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

/* Private define ------------------------------------------------------------*/
#define _UVC_CAM_HEIGHT (480)
#define _UVC_CAM_WIDTH  (640)
#define IMAGEHEIGHT     _UVC_CAM_HEIGHT
#define IMAGEWIDTH      _UVC_CAM_WIDTH

#define NB_BUFFER 4

/* Private macro -------------------------------------------------------------*/
/* Private typedef -----------------------------------------------------------*/
struct vdIn {
    int   fd;
    char* videodevice;

    // v4l2
    struct v4l2_capability     cap;
    struct v4l2_format         fmt;
    struct v4l2_fmtdesc        fmtdesc;
    struct v4l2_streamparm     setfps;
    struct v4l2_requestbuffers rb;

    void* mem[NB_BUFFER];
    int   memlength[NB_BUFFER];

    unsigned char* framebuffer;
    int            framesizeIn;

    int width;
    int height;
    int fps;


    FILE* fp_bmp;
};

/*_attribute__((packed))的作用是告诉编译器取消结构在编译过程中的优化对齐  */

//14byte文件头
typedef struct
{
    unsigned char cfType[2];  //文件类型,"BM"(0x4D42)
    unsigned int  cfSize;     //文件大小(字节)
    unsigned int  cfReserved; //保留,值为0
    unsigned int  cfoffBits;  //数据区相对于文件头的偏移量(字节)
} __attribute__((packed)) BITMAPFILEHEADER;


//40byte信息头
typedef struct
{
    unsigned int       ciSize;            //BITMAPFILEHEADER所占的字节数
    unsigned int       ciWidth;           //宽度
    unsigned int       ciHeight;          //高度
    unsigned short int ciPlanes;          //目标设备的位平面数,值为1
    unsigned short int ciBitCount;        //每个像素的位数
    char               ciCompress[4];     //压缩说明
    unsigned int       ciSizeImage;       //用字节表示的图像大小,该数据必须是4的倍数
    unsigned int       ciXPelsPerMeter;   //目标设备的水平像素数/米
    unsigned int       ciYPelsPerMeter;   //目标设备的垂直像素数/米
    unsigned int       ciClrUsed;         //位图使用调色板的颜色数
    unsigned           intciClrImportant; //指定重要的颜色数,当该域的值等于颜色数时(或者等于0时),表示所有颜色都一样重要
} __attribute__((packed)) BITMAPINFOHEADER;

typedef struct
{
    unsigned char blue;
    unsigned char green;
    unsigned char red;
} __attribute__((packed)) PIXEL; //颜色模式RGB



/* Private function prototypes -----------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
static struct vdIn   uvc_cam;
static unsigned char rgb888_buffer[IMAGEWIDTH * IMAGEHEIGHT * 3];

/* Global  variables ---------------------------------------------------------*/
/* Private functions ---------------------------------------------------------*/


void yuyv_to_rgb888(void)
{
    int            i, j;
    unsigned char  y1, y2, u, v;
    int            r1, g1, b1, r2, g2, b2;
    unsigned char* pointer;
    double         rbase = 0;
    double         gbase = 0;
    double         bbase = 0;


    pointer = uvc_cam.framebuffer;


    for (i = 0; i < IMAGEHEIGHT; i++) {
        for (j = 0; j < (IMAGEWIDTH / 2); j++) {
            y1 = *(pointer + ((i * (IMAGEWIDTH / 2) + j) << 2));
            u  = *(pointer + ((i * (IMAGEWIDTH / 2) + j) << 2) + 1);
            y2 = *(pointer + ((i * (IMAGEWIDTH / 2) + j) << 2) + 2);
            v  = *(pointer + ((i * (IMAGEWIDTH / 2) + j) << 2) + 3);


            rbase = 1.042 * (v - 128);
            gbase = 0.34414 * (u - 128) - 0.71414 * (v - 128);
            bbase = 1.772 * (u - 128);

            r1 = y1 + rbase;
            g1 = y1 - gbase;
            b1 = y1 + bbase;

            r2 = y2 + rbase;
            g2 = y2 - gbase;
            b2 = y2 + bbase;


            if (r1 > 255)
                r1 = 255;
            else if (r1 < 0)
                r1 = 0;

            if (b1 > 255)
                b1 = 255;
            else if (b1 < 0)
                b1 = 0;

            if (g1 > 255)
                g1 = 255;
            else if (g1 < 0)
                g1 = 0;

            if (r2 > 255)
                r2 = 255;
            else if (r2 < 0)
                r2 = 0;

            if (b2 > 255)
                b2 = 255;
            else if (b2 < 0)
                b2 = 0;

            if (g2 > 255)
                g2 = 255;
            else if (g2 < 0)
                g2 = 0;


            *(rgb888_buffer + ((IMAGEHEIGHT - 1 - i) * (IMAGEWIDTH / 2) + j) * 6)     = (unsigned char)b1;
            *(rgb888_buffer + ((IMAGEHEIGHT - 1 - i) * (IMAGEWIDTH / 2) + j) * 6 + 1) = (unsigned char)g1;
            *(rgb888_buffer + ((IMAGEHEIGHT - 1 - i) * (IMAGEWIDTH / 2) + j) * 6 + 2) = (unsigned char)r1;
            *(rgb888_buffer + ((IMAGEHEIGHT - 1 - i) * (IMAGEWIDTH / 2) + j) * 6 + 3) = (unsigned char)b2;
            *(rgb888_buffer + ((IMAGEHEIGHT - 1 - i) * (IMAGEWIDTH / 2) + j) * 6 + 4) = (unsigned char)g2;
            *(rgb888_buffer + ((IMAGEHEIGHT - 1 - i) * (IMAGEWIDTH / 2) + j) * 6 + 5) = (unsigned char)r2;
        }
    }

    printf("yuyv to rgb888 done\n");
}




int v4l2_init(void)
{
    int                i = 0;
    int                ret;
    struct v4l2_buffer buf;


    // 1. open cam
    if ((uvc_cam.fd = open(uvc_cam.videodevice, O_RDWR)) == -1) {
        printf("ERROR opening V4L interface\n");
        return -1;
    }

    // 2. querycap
    memset(&uvc_cam.cap, 0, sizeof(struct v4l2_capability));
    ret = ioctl(uvc_cam.fd, VIDIOC_QUERYCAP, &uvc_cam.cap);

    if (ret < 0) {
        printf("Error opening device %s: unable to query device.\n", uvc_cam.videodevice);
        return -1;
    }
    else {
        printf("driver:\t\t%s\n", uvc_cam.cap.driver);
        printf("card:\t\t%s\n", uvc_cam.cap.card);
        printf("bus_info:\t%s\n", uvc_cam.cap.bus_info);
        printf("version:\t%d\n", uvc_cam.cap.version);
        printf("capabilities:\t%x\n", uvc_cam.cap.capabilities);

        if ((uvc_cam.cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE) {
            printf("%s: \tsupports capture.\n", uvc_cam.videodevice);
        }

        if ((uvc_cam.cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING) {
            printf("%s: \tsupports streaming.\n", uvc_cam.videodevice);
        }
    }

    // 3. set format in

    // 3.1 enum fmt
    printf("\nSupport format:\n");

    memset(&uvc_cam.fmtdesc, 0, sizeof(struct v4l2_fmtdesc));
    uvc_cam.fmtdesc.index = 0;
    uvc_cam.fmtdesc.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    while (ioctl(uvc_cam.fd, VIDIOC_ENUM_FMT, &uvc_cam.fmtdesc) != -1) {
        printf("\t%d.%s\n", uvc_cam.fmtdesc.index + 1, uvc_cam.fmtdesc.description);
        uvc_cam.fmtdesc.index++;
    }

    // 3.2 set fmt
    memset(&uvc_cam.fmt, 0, sizeof(struct v4l2_format));
    uvc_cam.fmt.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    uvc_cam.fmt.fmt.pix.width       = uvc_cam.width;
    uvc_cam.fmt.fmt.pix.height      = uvc_cam.height;
    uvc_cam.fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    uvc_cam.fmt.fmt.pix.field       = V4L2_FIELD_ANY;

    ret = ioctl(uvc_cam.fd, VIDIOC_S_FMT, &uvc_cam.fmt);
    if (ret < 0) {
        printf("Unable to set format\n");
        return -1;
    }

    // 3.3 get fmt
    ret = ioctl(uvc_cam.fd, VIDIOC_G_FMT, &uvc_cam.fmt);
    if (ret < 0) {
        printf("Unable to get format\n");
        return -1;
    }
    else {
        printf("\nfmt.type:\t\t%d\n", uvc_cam.fmt.type);
        printf("pix.pixelformat:\t%c%c%c%c\n", uvc_cam.fmt.fmt.pix.pixelformat & 0xFF, (uvc_cam.fmt.fmt.pix.pixelformat >> 8) & 0xFF, (uvc_cam.fmt.fmt.pix.pixelformat >> 16) & 0xFF, (uvc_cam.fmt.fmt.pix.pixelformat >> 24) & 0xFF);
        printf("pix.height:\t\t%d\n", uvc_cam.fmt.fmt.pix.height);
        printf("pix.width:\t\t%d\n", uvc_cam.fmt.fmt.pix.width);
        printf("pix.field:\t\t%d\n", uvc_cam.fmt.fmt.pix.field);
    }


    // 4. set fps
    memset(&uvc_cam.setfps, 0, sizeof(struct v4l2_streamparm));
    uvc_cam.setfps.type                                  = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    uvc_cam.setfps.parm.capture.timeperframe.numerator   = 1;
    uvc_cam.setfps.parm.capture.timeperframe.denominator = 25;

    ret = ioctl(uvc_cam.fd, VIDIOC_S_PARM, &uvc_cam.setfps);

    if (ret < 0) {
        printf("Unable to set frame rate\n");
        return -1;
    }
    else {
        printf("set fps OK!\n");
    }

    ret = ioctl(uvc_cam.fd, VIDIOC_G_PARM, &uvc_cam.setfps);

    if (ret < 0) {
        printf("Unable to get frame rate\n");
        return -1;
    }
    else {
        printf("get fps OK:\n");
        printf("timeperframe.numerator  : %d\n", uvc_cam.setfps.parm.capture.timeperframe.numerator);
        printf("timeperframe.denominator: %d\n", uvc_cam.setfps.parm.capture.timeperframe.denominator);
        printf("set fps : %d\n", 1 * uvc_cam.setfps.parm.capture.timeperframe.denominator / uvc_cam.setfps.parm.capture.timeperframe.numerator);
    }

    // 5. enum framesizes

    while (1) {
        struct v4l2_fmtdesc fmtdesc;
        memset(&fmtdesc, 0, sizeof(struct v4l2_fmtdesc));
        fmtdesc.index = i++;
        fmtdesc.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE;

        if (ioctl(uvc_cam.fd, VIDIOC_ENUM_FMT, &fmtdesc) < 0) {
            break;
        }

        printf("Supported format: %s\n", fmtdesc.description);
        struct v4l2_frmsizeenum fsenum;
        memset(&fsenum, 0, sizeof(struct v4l2_frmsizeenum));
        fsenum.pixel_format = uvc_cam.fmtdesc.pixelformat;

        int j = 0;

        while (1) {
            fsenum.index = j;
            j++;

            if (ioctl(uvc_cam.fd, VIDIOC_ENUM_FRAMESIZES, &fsenum) == 0) {
                if (uvc_cam.fmt.fmt.pix.pixelformat == fmtdesc.pixelformat) {
                    printf("\tSupported size with the current format: %dx%d\n", fsenum.discrete.width, fsenum.discrete.height);
                }
                else {
                    printf("\tSupported size: %dx%d\n", fsenum.discrete.width, fsenum.discrete.height);
                }
            }
            else {
                break;
            }
        }
    }

    // 6. request buffers
    memset(&uvc_cam.rb, 0, sizeof(struct v4l2_requestbuffers));
    uvc_cam.rb.count  = NB_BUFFER;
    uvc_cam.rb.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    uvc_cam.rb.memory = V4L2_MEMORY_MMAP;

    ret = ioctl(uvc_cam.fd, VIDIOC_REQBUFS, &uvc_cam.rb);

    if (ret < 0) {
        printf("Unable to allocate buffers\n");
        return -1;
    }

    // 6.1 map the buffers

    for (i = 0; i < NB_BUFFER; i++) {
        memset(&buf, 0, sizeof(struct v4l2_buffer));
        buf.index  = i;
        buf.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;

        ret = ioctl(uvc_cam.fd, VIDIOC_QUERYBUF, &buf);
        if (ret < 0) {
            printf("Unable to query buffer\n");
            return -1;
        }

        uvc_cam.mem[i] = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, uvc_cam.fd, buf.m.offset);
        if (uvc_cam.mem[i] == MAP_FAILED) {
            printf("Unable to map buffer\n");
            return -1;
        }
        uvc_cam.memlength[i] = buf.length;
    }


    // 6.2 queue the buffers.
    for (i = 0; i < NB_BUFFER; i++) {
        memset(&buf, 0, sizeof(struct v4l2_buffer));
        buf.index  = i;
        buf.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        ret        = ioctl(uvc_cam.fd, VIDIOC_QBUF, &buf);
        if (ret < 0) {
            printf("Unable to queue buffer\n");
            return -1;
        }
    }

    // 7. malloc yuyv buf
    uvc_cam.framesizeIn = uvc_cam.width * uvc_cam.height << 1; // w * h * 2
    uvc_cam.framebuffer = (unsigned char*)calloc(1, (size_t)uvc_cam.framesizeIn);

    if (uvc_cam.framebuffer == NULL) {
        printf("err calloc memory\n");
        return -1;
    }

    printf("init %s \t[OK]\n", uvc_cam.videodevice);

    return 0;
}

void v4l2_exit(void)
{
    free(uvc_cam.framebuffer);
    close(uvc_cam.fd);
}

int v4l2_enable(void)
{
    int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    int ret;

    ret = ioctl(uvc_cam.fd, VIDIOC_STREAMON, &type);
    if (ret < 0) {
        printf("Unable to start capture\n");
        return ret;
    }

    printf("start capture\n");

    return 0;
}

int v4l2_disable(void)
{
    int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    int ret;

    ret = ioctl(uvc_cam.fd, VIDIOC_STREAMOFF, &type);
    if (ret < 0) {
        printf("Unable to stop capture\n");
        return ret;
    }

    printf("stop capture\n");

    return 0;
}

int v4l2_uvc_grap(void)
{
    int                ret;
    struct v4l2_buffer buf;


    memset(&buf, 0, sizeof(struct v4l2_buffer));
    buf.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;

    ret = ioctl(uvc_cam.fd, VIDIOC_DQBUF, &buf);
    if (ret < 0) {
        printf("Unable to dequeue buffer\n");
        exit(1);
    }

    memcpy(uvc_cam.framebuffer, uvc_cam.mem[buf.index], uvc_cam.framesizeIn);

    ioctl(uvc_cam.fd, VIDIOC_QBUF, &buf);

    printf("buf index: %d\n", buf.index);

    return 0;
}




int save_bmp(char* bmp_name)
{
    FILE*            fp;
    BITMAPFILEHEADER bf;
    BITMAPINFOHEADER bi;

    printf("save bmp  function\n");

    fp = fopen(bmp_name, "wb");
    if (fp == NULL) {
        printf("open errror\n");
        return (-1);
    }

    //Set BITMAPINFOHEADER
    memset(&bi, 0, sizeof(BITMAPINFOHEADER));
    bi.ciSize      = 40;
    bi.ciWidth     = IMAGEWIDTH;
    bi.ciHeight    = IMAGEHEIGHT;
    bi.ciPlanes    = 1;
    bi.ciBitCount  = 24;
    bi.ciSizeImage = IMAGEWIDTH * IMAGEHEIGHT * 3;


    //Set BITMAPFILEHEADER
    memset(&bf, 0, sizeof(BITMAPFILEHEADER));
    bf.cfType[0]  = 'B';
    bf.cfType[1]  = 'M';
    bf.cfSize     = 54 + bi.ciSizeImage;
    bf.cfReserved = 0;
    bf.cfoffBits  = 54;


    fwrite(&bf, 14, 1, fp);
    fwrite(&bi, 40, 1, fp);
    fwrite(rgb888_buffer, bi.ciSizeImage, 1, fp);

    printf("save %s done\n", bmp_name);

    fclose(fp);

    return 0;
}



int main(int argc, char const* argv[])
{
    char vdname[15];

    printf("\n----- v4l2 savebmp app start ----- \n");

    if (argc < 2) {

        printf("need:/dev/videox\n");
        printf("like:%s /dev/video1\n", argv[0]);

        printf("app exit.\n\n");
        exit(1);
    }

    snprintf(vdname, 12, argv[1]);

    memset(&uvc_cam, 0, sizeof(struct vdIn));
    uvc_cam.videodevice = vdname;
    printf("using: \t\t%s\n", uvc_cam.videodevice);


    uvc_cam.width  = _UVC_CAM_WIDTH;
    uvc_cam.height = _UVC_CAM_HEIGHT;

    // 1. init cam
    if (v4l2_init() < 0) {
        goto app_exit;
    }

    v4l2_enable();
    usleep(5 * 1000);

    // 2. grap uvc
    v4l2_uvc_grap();
    yuyv_to_rgb888();


    // 3. save bmp
    save_bmp("./uvc_grap.bmp");



app_exit:
    printf("app exit.\n\n");
    v4l2_exit();

    return 0;
}





/*************************** (C) COPYRIGHT 2020 ZYS ************END OF FILE****/


- 运行程序:

# ./av4l2grap-uvc-savebmp-x /dev/video1

----- v4l2 savebmp app start -----
using:          /dev/video1
driver:         uvcvideo
card:           Aoni HD Camera
bus_info:       usb-ci_hdrc.1-1.4
version:        262415
capabilities:   84200001
/dev/video1:    supports capture.
/dev/video1:    supports streaming.

Support format:
        1.MJPEG
        2.YUV 4:2:2 (YUYV)

fmt.type:               1
pix.pixelformat:        YUYV
pix.height:             480
pix.width:              640
pix.field:              1
set fps OK!
get fps OK:
timeperframe.numerator  : 1
timeperframe.denominator: 25
set fps : 25
Supported format: MJPEG
        Supported size: 640x480
        Supported size: 1280x720
        Supported size: 1184x656
        Supported size: 1024x576
        Supported size: 960x720
        Supported size: 960x540
        Supported size: 864x486
        Supported size: 800x600
        Supported size: 752x423
        Supported size: 640x360
        Supported size: 320x240
Supported format: YUV 4:2:2 (YUYV)
        Supported size with the current format: 640x480
        Supported size with the current format: 1280x720
        Supported size with the current format: 1184x656
        Supported size with the current format: 1024x576
        Supported size with the current format: 960x720
        Supported size with the current format: 960x540
        Supported size with the current format: 864x486
        Supported size with the current format: 800x600
        Supported size with the current format: 752x423
        Supported size with the current format: 640x360
        Supported size with the current format: 320x240
init /dev/video1        [OK]
start capture
buf index: 0
yuyv to rgb888 done
save bmp  function
save ./uvc_grap.bmp done
app exit.

- 拍照效果

拍屏幕效果不好,拍其它很清晰。

ubuntu-bmp.png

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