RPi-OpenCV_图像与视频载入、显示、输出

树莓派 OpenCV
图像处理
Publish Date:   2018-02-03
Update Date:   2023-09-13
Word Count:   1.6k
Read Times:   8 Min
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本章，在介绍了图像的基本数据结构之后，来学习图像的一些基本操作，包括图像的载入、显示、ROI、绘图、输出等，这些操作是后续进行图像处理的必备工具。

1 图像的载入,显示，与输出

1.1 Python3

现在通过一个demo来认识Python3中图像的载入，显示，与输出操作：

import cv2
import numpy as np

# default read as BGR picture
img1 = cv2.imread('color.jpg')
# show it in the window
cv2.imshow('image1',img1)
# write it to local disk
cv2.imwrite('image1.jpg',img1)

# read as grayscale picture
img2 = cv2.imread('color.jpg',cv2.IMREAD_GRAYSCALE)
# show it in the window
cv2.imshow('image2',img2)
# write it to local disk
cv2.imwrite('image2.jpg',img2)

cv2.waitKey(0)
cv2.destroyAllWindows()

实际运行效果如下图所示，在运行后，在python文件路径下可找到image1.jpg，image2.jpg文件，且image2.jpg是灰度图像。

1.2 cpp

cpp源码类似如下：

#include<opencv2/core/core.hpp>
#include<opencv2/highgui/highgui.hpp>
using namespace cv;

int main(void)
{
	Mat img1=imread("color.jpg");
	namedWindow("image1");
	imshow("image1",img1);
	imwrite("image1.jpg",img1);

	Mat img2=imread("color.jpg",IMREAD_GRAYSCALE);
	namedWindow("image2");
	imshow("image2",img2);
	imwrite("image2.jpg",img2);

	waitKey(0);
	return 0;
}

2 视频，摄像头的载入，显示

2.1 Python3

现在通过一个demo来理解Python3中视频，摄像头的载入与显示操作,且在该操作中，包含了摄像头的翻转，摄像头开窗定义等。

同时还包含了视频的载入，显示操作；注意，OpenCV只支持读取avi格式的视频，并且不包含音频。

import cv2

capCamera = cv2.VideoCapture(0)
if(not capCamera.isOpened()):
    print("can't open this camera")
    exit(0)

capVideo = cv2.VideoCapture('demo.avi')
if(not capVideo.isOpened()):
    print("can't open this video")
    exit(0)

# set the image width and height
capCamera.set(cv2.CAP_PROP_FRAME_WIDTH, 320)
capCamera.set(cv2.CAP_PROP_FRAME_HEIGHT, 240)

## image flip setup
# * horizontal flip:  flipCode = 1
# * Vertical flip:  flipCode = 0
# * horizontal & Vertical flip:  flipCode = -1
flipCode = -1

while(True):
    # handle for the camera
    ret, FrameCamera = capCamera.read()
    FrameCamera = cv2.flip(FrameCamera, flipCode)
    if ret == True:
        cv2.imshow('camera',FrameCamera)
    else:
        break
    
    # handle for the video
    ret, FrameVideo = capVideo.read()
    if ret == True:
        cv2.imshow('video',FrameVideo)
        FramVideoGray = cv2.cvtColor(FrameVideo,cv2.COLOR_BGR2GRAY)
        cv2.imshow('grayVideo',FramVideoGray)
    else:
        break
    
    # handle for exit
    if (cv2.waitKey(1)) == ord('q'):
        break

capCamera.release()
cv2.destroyAllWindows()

实际运行效果如下图所示：

2.2 cpp

其cpp源码类似如下：

#include<iostream>
#include<opencv2/opencv.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<opencv2/imgproc/imgproc.hpp>

using namespace std;
using namespace cv;

int main()
{
	VideoCapture capCamera(0);
	if(!capCamera.isOpened())
	{
		cout<<"can't open this camera"<<endl;
		return -1;
	}
	VideoCapture capVideo("demo.avi");
	if(!capVideo.isOpened())
	{
		cout<<"can't open this video"<<endl;
		return -1;
	}
	capCamera.set(CAP_PROP_FRAME_WIDTH, 320);
	capCamera.set(CAP_PROP_FRAME_HEIGHT, 240);

	Mat FrameCamera,FrameVideo;

	// image flip setup
	// horizontal flip:  flipCode = 1
	// Vertical flip:  flipCode = 0
	// horizontal & Vertical flip:  flipCode = -1
	int flipCode = -1;
	
	while(1)
	{	
		//read by operator ">>"
		capCamera>>FrameCamera;
		flip(FrameCamera,FrameCamera,flipCode);
		imshow("camera",FrameCamera);
		
		//read by function read
		bool ret = capVideo.read(FrameVideo);
		if(ret == true)
		{
			imshow("video",FrameVideo);
			cvtColor(FrameVideo,FrameVideo,COLOR_BGR2GRAY);
			imshow("grayVideo",FrameVideo);
		}
		else
		{
			break;
		}

		if(char(waitKey(1)) == 'q')
		{
			break;
		}
	}
	capCamera.release();
	capVideo.release();
	destroyAllWindows();
	return 0;
}

3 视频，摄像头的输出

本节主要讲解视频，摄像头的输出，即，将视频流数据保存到本地。

OpenCV只支持生成avi格式的视频，且生成的视频文件不能大于2G，且不能添加音频。

3.1 Python3

关于视频输出，主要用到VideoWriter对象，而视频的输入，主要用到VideoCapture对象，因此，视频的输出(视频录制)的主要过程就是将VideoCapture中读入的图片写入到VideoWriter当中，在给出demo程序之前，先给出VideoWrite的使用方法：

# Encode the video format as MJPG
fourcc = cv2.VideoWriter_fourcc('M','J','P','G')
print(fourcc)
# Config the framrate to 20 frame per second
# fps = capCamera.get(cv2.CAP_PROP_FPS)
fps = 20.0
print(fps)
# Config the Window Size by camera
frameSize = (int(capCamera.get(cv2.CAP_PROP_FRAME_WIDTH)),int(capCamera.get(cv2.CAP_PROP_FRAME_HEIGHT)))
print(frameSize)
# Create the VideoWrite Object
outCamera = cv2.VideoWriter('outputCamera.avi',fourcc,fps,frameSize)

首先，在写入视频的时候，必须先指定视频的编码格式，这里我们指定为MJPG格式。

fourcc = cv2.VideoWriter_fourcc('M','J','P','G')

接着，须指定视频的帧率跟窗口大小。

# Config the framrate to 20 frame per second
# fps = capCamera.get(cv2.CAP_PROP_FPS)
fps = 20.0
print(fps)
# Config the Window Size by camera
frameSize = (int(capCamera.get(cv2.CAP_PROP_FRAME_WIDTH)),int(capCamera.get(cv2.CAP_PROP_FRAME_HEIGHT)))
print(frameSize)

最后，初始化VideoWriter的时候，将这些参数传入到其中。并指定输出视频文件的名称。

# Create the VideoWrite Object
outCamera = cv2.VideoWriter('outputCamera.avi',fourcc,fps,frameSize)

接下来，将给出源码：

import cv2
import numpy as np

#--------------------------------
# set for camera
capCamera = cv2.VideoCapture(0)
capCamera.set(cv2.CAP_PROP_FRAME_WIDTH,640)
capCamera.set(cv2.CAP_PROP_FRAME_HEIGHT,480)

# set for camera output
fourcc = cv2.VideoWriter_fourcc('M','J','P','G')
print(fourcc)
# fps = capCamera.get(cv2.CAP_PROP_FPS)
fps = 20.0
print(fps)
frameSize = (int(capCamera.get(cv2.CAP_PROP_FRAME_WIDTH)),int(capCamera.get(cv2.CAP_PROP_FRAME_HEIGHT)))
print(frameSize)
outCamera = cv2.VideoWriter('outputCamera.avi',fourcc,fps,frameSize)
#--------------------------------

#--------------------------------
# set for video
capVideo = cv2.VideoCapture('demo1.avi')

# set for video output
fourcc = int(capVideo.get(cv2.CAP_PROP_FOURCC))
print(fourcc)
fps = capVideo.get(cv2.CAP_PROP_FPS)
print(fps)
frameSize = (int(capVideo.get(cv2.CAP_PROP_FRAME_WIDTH)),int(capVideo.get(cv2.CAP_PROP_FRAME_HEIGHT)))
print(frameSize)
outVideo = cv2.VideoWriter('outputVideo.avi',fourcc,fps,frameSize)
#--------------------------------

choose = input("Please input C or V:\n")

# Process for camera
if choose == 'C':
    while (capCamera.isOpened()):
        ret,frameCamera = capCamera.read()
        outCamera.write(frameCamera)
        cv2.imshow("frameCamera", frameCamera)
        if cv2.waitKey(1) == ord('q'):
            break

# Process for video
elif choose == 'V':
    while(capVideo.isOpened()):
        ret,frameVideo = capVideo.read()
        if ret:
            outVideo.write(frameVideo)
            cv2.imshow("framVideo", frameVideo)
        if cv2.waitKey(1)==ord('q'):
            break

else:
    print("Please input right order")

capCamera.release()
capVideo.release()

cv2.destroyAllWindows()

运行该代码后，将首先提示用户输入选项C(Camera)或V(Video)：当输入C之后，将打开摄像头，录制视频，并将视频保存到本地；当输入V之后，将打开本地的视频，将本地的视频重新写入到本地。

3.2 cpp

其cpp源码类似如下：

#include<iostream>
#include<opencv2/opencv.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<opencv2/imgproc/imgproc.hpp>

using namespace std;
using namespace cv;

int main()
{
	//set for camera
	//---------------------------------------
	VideoCapture capCamera(0);
	if(!capCamera.isOpened())
	{
		cout<<"can't open this camera"<<endl;
		return -1;
	}
	capCamera.set(CAP_PROP_FRAME_WIDTH, 640);
	capCamera.set(CAP_PROP_FRAME_HEIGHT, 480);
	int fourcc = VideoWriter::fourcc('M','J','P','G');
	printf("%d\r\n",fourcc);
	//double fps = capCamera.get(CAP_PROP_FPS);
	double fps = 20.0;
	Size frameSize = Size((int)capCamera.get(CAP_PROP_FRAME_WIDTH),(int)capCamera.get(CAP_PROP_FRAME_HEIGHT));
	printf("%d,%d\r\n",(int)capCamera.get(CAP_PROP_FRAME_WIDTH),(int)capCamera.get(CAP_PROP_FRAME_HEIGHT));
	VideoWriter outCamera;
	outCamera.open("outputCamera.avi",fourcc,fps,frameSize);
	//---------------------------------------
	

	//set for video
	//---------------------------------------
	VideoCapture capVideo("demo.avi");
	if(!capVideo.isOpened())
	{
		cout<<"can't open this video"<<endl;
		return -1;
	}
	fourcc = VideoWriter::fourcc('M','J','P','G');
	printf("%d\r\n",fourcc);
	//fps = capCVideo.get(CAP_PROP_FPS);
	fps = 20.0;
	frameSize = Size((int)capVideo.get(CAP_PROP_FRAME_WIDTH),(int)capVideo.get(CAP_PROP_FRAME_HEIGHT));
	printf("%d,%d\r\n",(int)capVideo.get(CAP_PROP_FRAME_WIDTH),(int)capVideo.get(CAP_PROP_FRAME_HEIGHT));
	VideoWriter outVideo;
	outVideo.open("outputVideo.avi",fourcc,fps,frameSize);
	//---------------------------------------
	
	char choose;
	printf("Please input C or V \r\n");
	scanf("%c",&choose);
	
	Mat frameCamera, frameVideo;
	
	if(choose == 'C')
	{
		while(capCamera.isOpened())
		{
			capCamera>>frameCamera;
			outCamera.write(frameCamera);
			imshow("frameCamera", frameCamera);
			if(char(waitKey(1)) == 'q')
			{
				break;
			}		
		}
	}
	
	else if(choose == 'V')
	{
		while(capVideo.isOpened())
		{
			bool ret = capVideo.read(frameVideo);
			if(ret)
			{
				outVideo.write(frameVideo);
            	imshow("framVideo", frameVideo)	;
			}
			if(char(waitKey(1)) == 'q')
			{
				break;
			}
		}
	}
	else
	{
		printf("Please input right order");
	}
	capCamera.release();
	capVideo.release();
	destroyAllWindows();

	return 0;
}

其cpp源码运行效果同Python源码。

Author: Ruimin Huang
Link: http://www.huangruimin.tech/2018/02/03/rpi-opencv-tu-xiang-yu-shi-pin-zai-ru-xian-shi-shu-chu/
Reprint policy: All articles in this blog are used except for special statements CC BY 4.0 reprint polocy. If reproduced, please indicate source Ruimin Huang !
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