V4L2 獲取和配置攝像頭程序示例：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <error.h>
#include <string.h>
#include <fcntl.h>
#include <linux/videodev2.h>
int fd;
const char *input_dev = "/dev/video0";
const char *qctrl_name = NULL;
int qctrl_value = 0;
struct v4l2_capability cap;
struct v4l2_queryctrl qctrl;
static void print_qctrl(struct v4l2_queryctrl *qctrl)
{
struct v4l2_control ctrl;
ctrl.id = qctrl->id;
if (ioctl(fd, VIDIOC_G_CTRL, &ctrl) < 0) {
perror("get ctrl failed");
ctrl.value = -999;
}
printf("%-14s : id=%08x, type=%d, minimum=%d, maximum=%d\n"
"\t\t value = %d, step=%d, default_value=%d\n",
qctrl->name, qctrl->id, qctrl->type, qctrl->minimum, qctrl->maximum,
ctrl.value, qctrl->step, qctrl->default_value);
}
static void print_menu(struct v4l2_querymenu *menu)
{
printf("\t %d : %s\n", menu->index, menu->name);
}
static int set_qctrl(struct v4l2_queryctrl *qctrl)
{
struct v4l2_control ctrl;
printf("set %s = %d\n", qctrl_name, qctrl_value);
ctrl.id = qctrl->id;
ctrl.value = qctrl_value;
return ioctl(fd, VIDIOC_S_CTRL, &ctrl);
}
static void deal_qctrl(struct v4l2_queryctrl *qctrl)
{
print_qctrl(qctrl);
if (qctrl_name && !strcmp(qctrl_name, qctrl->name))
set_qctrl(qctrl);
}
static void qctrl_get(int id)
{
qctrl.id = id;
if (ioctl(fd, VIDIOC_QUERYCTRL, &qctrl) == 0) {
deal_qctrl(&qctrl);
if (qctrl.type == V4L2_CTRL_TYPE_MENU) {
int idx;
struct v4l2_querymenu menu;
for (idx = qctrl.minimum; idx <= qctrl.maximum; idx++) {
menu.id = qctrl.id;
menu.index = idx;
if (ioctl(fd, VIDIOC_QUERYMENU, &menu)==0) {
print_menu(&menu);
}
}
}
}
}
int main(int argc, char **argv)
{
int ret, i;
if (argc == 3) {
qctrl_name = argv[1];
qctrl_value = atoi(argv[2]);
}
fd = open(input_dev, O_RDWR);
if (fd < 0) {
perror("open video failed");
return -1;
}
printf("open video '%s' success\n", input_dev);
ret = ioctl(fd, VIDIOC_QUERYCAP, &cap);
if (ret < 0) {
perror("ioctl querycap");
return -1;
}
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == 0) {
printf("video device donot support capture\n");
return -1;
}
for (i = V4L2_CID_BASE; i < V4L2_CID_LASTP1; i++) {
qctrl_get(i);
}
for (i = V4L2_CID_PRIVATE_BASE; i < V4L2_CID_PRIVATE_BASE+25; i++) {
qctrl_get(i);
}
printf("close video\n");
close(fd);
}
程序運行說明：
本程序是攝像頭參數獲取和配置的示例程序，所以系統必須帶有攝像頭驅動程序及攝像頭傳感器
程序參數說明：
不帶任何參數，則顯示攝像頭可配置的參數，即其當前配置值
www.linuxidc.com @linuxidc$ ./a.out
open video '/dev/video0' success
Brightness : id=00980900, type=1, minimum=0, maximum=255
value = 10, step=1, default_value=128
Contrast : id=00980901, type=1, minimum=0, maximum=256
value = 128, step=1, default_value=128
Gamma : id=00980910, type=1, minimum=1, maximum=6
value = 4, step=1, default_value=4
Auto Gain : id=00980912, type=2, minimum=0, maximum=1
value = 1, step=1, default_value=1
Light frequency filter : id=00980918, type=3, minimum=0, maximum=2
value = 1, step=1, default_value=1
0 : NoFliker
1 : 50 Hz
2 : 60 Hz
close video
帶兩個參數，第一個是要配置選項的名稱，第二項為其對應的值。
www.linuxidc.com @linuxidc$ ./a.out Brightness 50
open video '/dev/video0' success
Brightness : id=00980900, type=1, minimum=0, maximum=255
value = 10, step=1, default_value=128
set Brightness = 50
Contrast : id=00980901, type=1, minimum=0, maximum=256
value = 128, step=1, default_value=128
Gamma : id=00980910, type=1, minimum=1, maximum=6
value = 4, step=1, default_value=4
Auto Gain : id=00980912, type=2, minimum=0, maximum=1
value = 1, step=1, default_value=1
Light frequency filter : id=00980918, type=3, minimum=0, maximum=2
value = 1, step=1, default_value=1
0 : NoFliker
1 : 50 Hz
2 : 60 Hz
close video
程序原理說明：
本程序可簡要使用如下序列說明其運行過程：
1. fd = open(input_dev, O_RDWR); 打開 /dev/video0 設備
2. ret = ioctl(fd, VIDIOC_QUERYCAP, &cap); 獲取攝像頭設備的能力，例如照相、輸出、VBI、調頻什麼的。這裡只需照相能力
3. ioctl(fd, VIDIOC_QUERYCTRL, &qctrl); 通過id來枚舉出取攝像頭的queryctrl，這個結構體用來描述攝像頭的某個具體參數選項的(亮度、色度、曝光度什麼的)， 包括id, 名稱、類型、極值和默認值。
4. ioctl(fd, VIDIOC_QUERYMENU, &menu); 如果上面獲取的queryctrl類型是菜單類型的，可使用該步驟來列出所有的菜單項名稱。 這一步不是必須的，只是為了讓人更清除的知道queryctrl中每個值代表著什麼含義。例如 "Light frequency filter" 這個選項的取值范圍是 0~2, 3個菜單項說明其3個值的用途。
5. ioctl(fd, VIDIOC_S_CTRL, &ctrl) 和 ioctl(fd, VIDIOC_G_CTRL, &ctrl) 分別是設置和獲取參數項當前值的接口，只需指出要配置參數項的id即可。
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以上幾個所涉及的接口體可在 /usr/include/linux/videodev2.h 文件中找到。
/*
* C O N T R O L S
*/
struct v4l2_control {
__u32 id;
__s32 value;
};
/* Used in the VIDIOC_QUERYCTRL ioctl for querying controls */
struct v4l2_queryctrl {
__u32 id;
enum v4l2_ctrl_type type;
__u8 name[32]; /* Whatever */
__s32 minimum; /* Note signedness */
__s32 maximum;
__s32 step;
__s32 default_value;
__u32 flags;
__u32 reserved[2];
};
/* Used in the VIDIOC_QUERYMENU ioctl for querying menu items */
struct v4l2_querymenu {
__u32 id;
__u32 index;
__u8 name[32]; /* Whatever */
__u32 reserved;
};
/*
* D R I V E R C A P A B I L I T I E S
*/
struct v4l2_capability {
__u8 driver[16]; /* i.e. "bttv" */
__u8 card[32]; /* i.e. "Hauppauge WinTV" */
__u8 bus_info[32]; /* "PCI:" + pci_name(pci_dev) */
__u32 version; /* should use KERNEL_VERSION() */
__u32 capabilities; /* Device capabilities */
__u32 reserved[4];
};