如何利用网络摄像头Windows终端拍摄图片

Question

下面的代码旨在通过windows使用摄像头拍摄一张照片。当我运行代码时，摄像头的引导打开几秒钟(显示它被调用了)，然后保存PNG图像，但是它是由back像素(3kb)填充的。我不熟悉windows，所以解决这个问题可能很简单。有人能猜到是怎么回事吗？

package main

import (
    "bytes"
    "fmt"
    "io"
    "io/ioutil"
    "os"
    "os/exec"
    "syscall"
    "unsafe"
)

var (
    avicap32                    = syscall.NewLazyDLL("avicap32.dll")
    proccapCreateCaptureWindowA = avicap32.NewProc("capCreateCaptureWindowA")

    user32           = syscall.NewLazyDLL("user32.dll")
    procSendMessageA = user32.NewProc("SendMessageA")
)

func CaptureWebcam() {
    var name = "WebcamCapture"
    handle, _, _ := proccapCreateCaptureWindowA.Call(uintptr(unsafe.Pointer(&name)), 0, 0, 0, 320, 240, 0, 0)
    procSendMessageA.Call(handle, 0x40A, 0, 0)  //WM_CAP_DRIVER_CONNECT
    procSendMessageA.Call(handle, 0x432, 30, 0) //WM_CAP_SET_PREVIEW
    procSendMessageA.Call(handle, 0x43C, 0, 0)  //WM_CAP_GRAB_FRAME
    procSendMessageA.Call(handle, 0x41E, 0, 0)  //WM_CAP_EDIT_COPY
    procSendMessageA.Call(handle, 0x40B, 0, 0)  //WM_CAP_DRIVER_DISCONNECT
    camera, err := os.Create("Image.png")
    if err != nil {
        fmt.Println(err)
        return
    }
    clip, err := readClipboard()
    if err != nil {
        fmt.Println(err)
        return
    }
    _, err = io.Copy(camera, clip)
    if err != nil {
        fmt.Println(err)
        return
    }
    camera.Close()
}

func readClipboard() (io.Reader, error) {
    f, err := ioutil.TempFile("", "")
    if err != nil {
        fmt.Println(err)
        return nil, err
    }
    f.Close()
    _, err = exec.Command("PowerShell", "-Command", "Add-Type", "-AssemblyName", fmt.Sprintf("System.Windows.Forms;$clip=[Windows.Forms.Clipboard]::GetImage();if ($clip -ne $null) { $clip.Save('%s') };", f.Name())).CombinedOutput()
    if err != nil {
        fmt.Println(err)
        return nil, err
    }
    r := new(bytes.Buffer)
    file, err := os.Open(f.Name())
    if err != nil {
        fmt.Println(err)
        return nil, err
    }
    if _, err := io.Copy(r, file); err != nil {
        fmt.Println(err)
        return nil, err
    }
    file.Close()
    os.Remove(f.Name())
    return r, nil
}

func main() {
    CaptureWebcam()
}

Answer 1

数据似乎是位图剪贴板格式。您也可以直接使用剪贴板API。

来自文件样本的代码片段。

                case CF_BITMAP: 
                    hdcMem = CreateCompatibleDC(hdc); 
                    if (hdcMem != NULL) 
                    { 
                        if (OpenClipboard(hwnd)) 
                        { 
                            hbm = (HBITMAP) 
                                GetClipboardData(uFormat); 
                            SelectObject(hdcMem, hbm); 
                            GetClientRect(hwnd, &rc); 
 
                            BitBlt(hdc, 0, 0, rc.right, rc.bottom, 
                                hdcMem, 0, 0, SRCCOPY); 
                            CloseClipboard(); 
                        } 
                        DeleteDC(hdcMem); 
                    } 
                    break;

附加了另一个代码从易数码相机连接。

void CYourProject::OnTimer(UINT nIDEvent) 
{
 if(nIDEvent==1)// First Timer
 {
   capGrabFrame(hWndC); // simple macro that sample a single frame from the 
                        // camera.
   capEditCopy(hWndC);  // simple macro that edit a copy of the frame.
   OpenClipboard();     //like virtual memory.
 
   //m_hBmp is a Handle to Bitmap.
   m_hBmp = (HBITMAP)::GetClipboardData(CF_BITMAP); 
   CloseClipboard();
 
   //...
 }
 CDialog::OnTimer(nIDEvent);
}