环境：ubuntu18.04 opencv4.4.0
摄像头：usb摄像头，挺老的摄像头，还是usb2.0的
csi摄像头也支持这种方法
插入摄像头后 ls /dev可以看到 /dev/video0
video后面的数字就是后面需要的设备id
代码段摘自opencv手册，基本使用这段代码就够用了
#include <opencv2/core.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>
#include <iostream>
#include <stdio.h>
using namespace cv;
using namespace std;
int main(int, char**)
{
Mat frame;
//--- INITIALIZE VIDEOCAPTURE
VideoCapture cap;
// open the default camera using default API
// cap.open(0);
// OR advance usage: select any API backend
int deviceID = 0; // 0 = open default camera
int apiID = cv::CAP_ANY; // 0 = autodetect default API
// open selected camera using selected API
cap.open(deviceID, apiID);
// check if we succeeded
if (!cap.isOpened()) {
cerr << "ERROR! Unable to open camera\n";
return -1;
}
//--- GRAB AND WRITE LOOP
cout << "Start grabbing" << endl
<< "Press any key to terminate" << endl;
for (;;)
{
// wait for a new frame from camera and store it into 'frame'
cap.read(frame);
// check if we succeeded
if (frame.empty()) {
cerr << "ERROR! blank frame grabbed\n";
break;
}
// show live and wait for a key with timeout long enough to show images
imshow("Live", frame);
if (waitKey(5) >= 0)
break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
API选择
在linux下自然选择v4l2，也可以用CAP_ANY让opencv自己选择，在linux下gstreamer也是基于V4L实现的，所以gstreamer和v4l2都可以。
需要注意的是，在编译opencv时就要把WITH_V4L打勾，好在在默认情况下WITH_V4L是勾选的
| enum |
cv::VideoCaptureAPIs {
cv::CAP_ANY = 0,
cv::CAP_VFW = 200,
cv::CAP_V4L = 200,
cv::CAP_V4L2 = CAP_V4L,
cv::CAP_FIREWIRE = 300,
cv::CAP_FIREWARE = CAP_FIREWIRE,
cv::CAP_IEEE1394 = CAP_FIREWIRE,
cv::CAP_DC1394 = CAP_FIREWIRE,
cv::CAP_CMU1394 = CAP_FIREWIRE,
cv::CAP_QT = 500,
cv::CAP_UNICAP = 600,
cv::CAP_DSHOW = 700,
cv::CAP_PVAPI = 800,
cv::CAP_OPENNI = 900,
cv::CAP_OPENNI_ASUS = 910,
cv::CAP_ANDROID = 1000,
cv::CAP_XIAPI = 1100,
cv::CAP_AVFOUNDATION = 1200,
cv::CAP_GIGANETIX = 1300,
cv::CAP_MSMF = 1400,
cv::CAP_WINRT = 1410,
cv::CAP_INTELPERC = 1500,
cv::CAP_REALSENSE = 1500,
cv::CAP_OPENNI2 = 1600,
cv::CAP_OPENNI2_ASUS = 1610,
cv::CAP_GPHOTO2 = 1700,
cv::CAP_GSTREAMER = 1800,
cv::CAP_FFMPEG = 1900,
cv::CAP_IMAGES = 2000,
cv::CAP_ARAVIS = 2100,
cv::CAP_OPENCV_MJPEG = 2200,
cv::CAP_INTEL_MFX = 2300,
cv::CAP_XINE = 2400
} |
CAP_PROP属性
高分辨率下有时延：在缺省情况下用VideoCapture打开摄像头，小分辨率640x480可以实时显示，但1920x1080时就会有将近1秒多的时延，这是不可接受的的事情
解决：用set接口将buffersize改小，使得高分辨率下也可以实时显示
cap.set(cv::CAP_PROP_BUFFERSIZE,1)；
尝试过修改CAP_PROP_FPS，发现效果并没有改变，猜测这不是一个从软件层面限制帧率的接口，而是与硬件通信修改帧率，而我的摄像头是固定帧率，所以这个属性并不生效，手册中许多属性后面都有一句only for those cameras that support
大部分摄像头的属性我都没有通过设定这些属性而成功，我的摄像头是支持VISCA协议的，我是通过这个协议来设定摄像头属性的，尚不清楚哪些摄像头能够支持这些CAP_PROP
常用的已标红
frame_width，frame_height：图像长宽
fourcc：四个字母用于表示图像格式，当不能自主识别时就需要自行设定
buffersize：缓冲区 value 0-10
| enum |
cv::VideoCaptureProperties {
cv::CAP_PROP_POS_MSEC =0,
cv::CAP_PROP_POS_FRAMES =1,
cv::CAP_PROP_POS_AVI_RATIO =2,
cv::CAP_PROP_FRAME_WIDTH =3,
cv::CAP_PROP_FRAME_HEIGHT =4,
cv::CAP_PROP_FPS =5,
cv::CAP_PROP_FOURCC =6,
cv::CAP_PROP_FRAME_COUNT =7,
cv::CAP_PROP_FORMAT =8,
cv::CAP_PROP_MODE =9,
cv::CAP_PROP_BRIGHTNESS =10,
cv::CAP_PROP_CONTRAST =11,
cv::CAP_PROP_SATURATION =12,
cv::CAP_PROP_HUE =13,
cv::CAP_PROP_GAIN =14,
cv::CAP_PROP_EXPOSURE =15,
cv::CAP_PROP_CONVERT_RGB =16,
cv::CAP_PROP_WHITE_BALANCE_BLUE_U =17,
cv::CAP_PROP_RECTIFICATION =18,
cv::CAP_PROP_MONOCHROME =19,
cv::CAP_PROP_SHARPNESS =20,
cv::CAP_PROP_AUTO_EXPOSURE =21,
cv::CAP_PROP_GAMMA =22,
cv::CAP_PROP_TEMPERATURE =23,
cv::CAP_PROP_TRIGGER =24,
cv::CAP_PROP_TRIGGER_DELAY =25,
cv::CAP_PROP_WHITE_BALANCE_RED_V =26,
cv::CAP_PROP_ZOOM =27,
cv::CAP_PROP_FOCUS =28,
cv::CAP_PROP_GUID =29,
cv::CAP_PROP_ISO_SPEED =30,
cv::CAP_PROP_BACKLIGHT =32,
cv::CAP_PROP_PAN =33,
cv::CAP_PROP_TILT =34,
cv::CAP_PROP_ROLL =35,
cv::CAP_PROP_IRIS =36,
cv::CAP_PROP_SETTINGS =37,
cv::CAP_PROP_BUFFERSIZE =38,
cv::CAP_PROP_AUTOFOCUS =39,
cv::CAP_PROP_SAR_NUM =40,
cv::CAP_PROP_SAR_DEN =41,
cv::CAP_PROP_BACKEND =42,
cv::CAP_PROP_CHANNEL =43,
cv::CAP_PROP_AUTO_WB =44,
cv::CAP_PROP_WB_TEMPERATURE =45,
cv::CAP_PROP_CODEC_PIXEL_FORMAT =46,
cv::CAP_PROP_BITRATE =47
} |
