如何使用OpenCV為桌面和Web構(gòu)建簡(jiǎn)單的Webcam應(yīng)用程序(二）
Dynamic Web TWAIN是一個(gè)專為Web應(yīng)用程序設(shè)計(jì)的TWAIN掃描識(shí)別控件。你只需在TWAIN接口寫幾行代碼，就可以用兼容TWAIN的掃描儀掃描文檔或從數(shù)碼相機(jī)/采集卡中獲取圖像。然后用戶可以編輯圖像并將圖像保存為多種格式，用戶可保存圖像到遠(yuǎn)程數(shù)據(jù)庫(kù)或者SharePoint。這個(gè)TWAIN控件還支持上傳和處理本地圖像。
點(diǎn)擊下載Dynamic Web TWAIN正式版
在大流行期間，由于社交距離遙遠(yuǎn)，對(duì)相機(jī)應(yīng)用程序的需求激增。因此，我收集了一些用不同編程語(yǔ)言實(shí)現(xiàn)的基本OpenCV網(wǎng)絡(luò)攝像頭示例代碼，并構(gòu)建了一些用于遠(yuǎn)程網(wǎng)絡(luò)攝像頭訪問(wèn)的簡(jiǎn)單Web應(yīng)用程序。希望這對(duì)開始構(gòu)建網(wǎng)絡(luò)攝像頭應(yīng)用程序的人有所幫助。在本文中，我將使用JavaScript，C＃，Python和Golang。
從任何Web瀏覽器訪問(wèn)遠(yuǎn)程網(wǎng)絡(luò)攝像頭
要實(shí)現(xiàn)遠(yuǎn)程網(wǎng)絡(luò)攝像頭訪問(wèn)，我只需要?jiǎng)?chuàng)建一個(gè)帶有圖像元素的簡(jiǎn)單HTML頁(yè)面并啟動(dòng)一個(gè)簡(jiǎn)單的HTTP服務(wù)器，即可通過(guò)HTTP GET請(qǐng)求連續(xù)發(fā)送網(wǎng)絡(luò)攝像頭幀。為了使代碼盡可能簡(jiǎn)單，我只使用了四種編程語(yǔ)言的內(nèi)置HTTP API和OpenCV視頻捕獲API。
Node.js
創(chuàng)建一個(gè)簡(jiǎn)單的HTML頁(yè)面：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Webcam</title>
</head>
<body>
<img id="image"/>
<script type="text/javascript">
var image = document.getElementById('image');
function refresh() {
image.src = "/image?" + new Date().getTime();
image.onload= function(){
setTimeout(refresh, 30);
}
}
refresh();
</script>
</body>
</html>
在服務(wù)器端，使用HTTP模塊創(chuàng)建一個(gè)簡(jiǎn)單的Web服務(wù)器：
const http = require('http');
var server = http.createServer(function (req, res) {
if (req.url === '/' || req.url === '/index.htm') {
res.writeHead(200, { 'Content-Type': 'text/html' });
res.write(html);
res.end();
}
else if (req.url.startsWith("/image")) {
res.writeHead(200, { 'Content-Type': 'image/jpeg' });
res.write(img);
res.end();
}
else
res.end('Invalid Request!');
});
server.listen(2020);
分析請(qǐng)求URL，然后發(fā)送相應(yīng)的響應(yīng)。同時(shí)，創(chuàng)建一個(gè)計(jì)時(shí)器以捕獲網(wǎng)絡(luò)攝像頭幀并將其編碼為JPEG格式：var img = null;
function capture() {
var frame = wCap.read()
if (frame.empty) {
wCap.reset();
frame = wCap.read();
}
img = cv.imencode('.jpg', frame);
setTimeout(capture, 30);
}
capture();
要通過(guò)雙擊打開HTML文件，請(qǐng)將相對(duì)圖像路徑更改為絕對(duì)圖像路徑：image.src = "http://localhost:2020/image?" + new Date().getTime();C＃
受本杰明·薩默頓（Benjamin Summerton）的要旨啟發(fā)，我創(chuàng)建了HTTP服務(wù)器，如下所示：
using System;
using System.IO;
using System.Text;
using System.Net;
using System.Threading.Tasks;
using OpenCvSharp;
namespace Web
{
class Program
{
public static HttpListener listener;
public static string url = "http://localhost:2020/";
public static string pageData =
"" +
"" +
"" +
"
HttpListener Example
" +
"" +
"" +
"![]()
"+
"
"+
"" +
"";
public static VideoCapture capture = new VideoCapture(0);
public static async Task HandleIncomingConnections()
{
while (true)
{
HttpListenerContext ctx = await listener.GetContextAsync();
HttpListenerRequest req = ctx.Request;
HttpListenerResponse resp = ctx.Response;
if ((req.HttpMethod == "GET") && (req.Url.AbsolutePath.StartsWith("/image"))) {
resp.ContentType = "image/jpeg";
using (Mat image = new Mat())
{
capture.Read(image);
Cv2.ImEncode(".jpg", image, out var imageData);
await resp.OutputStream.WriteAsync(imageData, 0, imageData.Length);
resp.Close();
}
}
else {
// Write the response info
byte[] data = Encoding.UTF8.GetBytes(pageData);
resp.ContentType = "text/html";
resp.ContentEncoding = Encoding.UTF8;
resp.ContentLength64 = data.LongLength;
// Write out to the response stream (asynchronously), then close it
await resp.OutputStream.WriteAsync(data, 0, data.Length);
resp.Close();
}
}
}
static void Main(string[] args)
{
// Create a Http server and start listening for incoming connections
listener = new HttpListener();
listener.Prefixes.Add(url);
listener.Start();
Console.WriteLine("Listening for connections on {0}", url);
// Handle requests
Task listenTask = HandleIncomingConnections();
listenTask.GetAwaiter().GetResult();
// Close the listener
listener.Close();
}
}
}
Python
使用Python的內(nèi)置HTTP服務(wù)器類非常方便。我們需要做的是定義一個(gè)用于處理HTTP請(qǐng)求的自定義處理程序：
import http.server
import socketserver
class MyHandler(http.server.BaseHTTPRequestHandler):
def do_GET(self):
if self.path == '/':
self.send_response(200)
self.send_header("Content-type", "text/html")
self.end_headers()
self.wfile.write(bytes(pageData, "utf8"))
elif self.path.startswith('/image'):
self.send_response(200)
self.send_header("Content-type", "image/jpeg")
self.end_headers()
ret, frame = cap.read()
_, jpg = cv2.imencode(".jpg", frame)
self.wfile.write(jpg)
else:
self.send_response(404)
with socketserver.TCPServer(("", PORT), MyHandler) as httpd:
print("Serving at port ", PORT)
try:
httpd.serve_forever()
except:
pass
Goang像Python一樣，很容易在30秒內(nèi)設(shè)置HTTP Web服務(wù)器：
func handler(w http.ResponseWriter, r *http.Request) {
if r.URL.Path == "/" {
pageData := "" +
"" +
"" +
"
HttpListener Example
" +
"" +
"" +
"![]()
" +
"
" +
"" +
""
w.Header().Set("Content-Type", "text/html")
w.Write([]byte(pageData))
} else if strings.HasPrefix(r.URL.Path, "/image") {
webcam.Read(&img)
jpg, _ := gocv.IMEncode(".jpg", img)
w.Write(jpg)
} else {
fmt.Fprintf(w, "Page Not Found")
}
}
func main() {
fmt.Println("Running at port 2020...")
webcam, _ = gocv.OpenVideoCapture(0)
img = gocv.NewMat()
http.HandleFunc("/", handler)
log.Fatal(http.ListenAndServe(":2020", nil))
webcam.Close()
}
完成所有操作后，我可以運(yùn)行Web服務(wù)器并訪問(wèn)localhost：2020以從任何桌面Web瀏覽器查看網(wǎng)絡(luò)攝像頭視頻流。
也可以從我的移動(dòng)網(wǎng)絡(luò)瀏覽器訪問(wèn)該頁(yè)面。
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