How Take A Picture Using Webcam Windows Terminal

Question

The code below aims to take a picture using the webcam via windows API. When I run the code the led of the webcam turns on (what indicates that it was called) for few seconds and then saves the PNG image, nevertheless it is complete filled of back pixels (3 kb). I am not familiar with windows API, so maybe solve this issue could be very simple. Anyone can guess what is going on?

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()
}

user_15511041 · Answer

It seems the data is CF_BITMAP Clipboard Format. Also you can use Clipboard API directly.

The code snippet from document sample.

                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;

Attached another Code from Easy Digital Camera Connection.

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);
}

How Take A Picture Using Webcam Windows Terminal

1 Answers