Question

我正在使用Windows API使用附加的网络摄像头拍照。

除了拍摄的照片非常暗以外，一切正常。如果我在另一个应用程序中启动网络摄像头然后我用我的应用程序捕获，一切正常。我做错了什么？

以下是我使用的代码：

procedure TWebCam.Execute; //different thread
var
  hand: THandle;
  fname: AnsiString;
const
  WM_CAP_START = $0400;
  WM_CAP_DRIVER_CONNECT = $0400 + 10;
  WM_CAP_DRIVER_DISCONNECT = $0400 + 11;
  WM_CAP_SAVEDIB = $0400 + 25;
  WM_CAP_GRAB_FRAME = $0400 + 60;
  WM_CAP_STOP = $0400 + 68;
  WM_CAP_SET_PREVIEW = WM_CAP_START + 50;
  WM_CAP_SET_PREVIEWRATE = WM_CAP_START + 52;
  WM_CAP_SET_SCALE = WM_CAP_START + 53;
begin
  FreeOnTerminate := True;
  fname := AnsiString(IncludeTrailingPathDelimiter(ExtractFilePath(ParamStr(0))) +
    'capture.bmp');
  if FileExists(String(fname)) then DeleteFile(string(fname));
  hand := capCreateCaptureWindowA('CapWindow32', WS_CHILD and WS_VISIBLE, 0, 0,
    0, 0, frmMain.Handle, 0);
  if hand <> 0 then
  begin
    if SendMessage(hand, WM_CAP_DRIVER_CONNECT, 0, 0) <> 0 then
    begin
      SendMessage(hand,WM_CAP_SET_PREVIEWRATE,66,0); //tried some stuff that are not required but without any success
      SendMessage(hand, WM_CAP_SET_PREVIEW, 1, 0);
      Sleep(5000);
      SendMessage(hand, WM_CAP_GRAB_FRAME, 0, 0);
      SendMessage(hand, WM_CAP_SAVEDIB, 0, NativeInt(PAnsichar(fname)));
      SendMessage(hand, WM_CAP_DRIVER_DISCONNECT, 0, 0);
      SendMessage(hand, $0010, 0, 0);
      SendMessage(frmMain.Handle,WM_USER + 24,0,0); //notify main thread
    end
    else
    begin
      SendMessage(hand, $0010, 0, 0);
      Synchronize(NoWebcam);
    end;
  end
  else
    Synchronize(NoWebcam);
end;

Answer 1

我讨厌给自己的问题一个答案，但也许有人会发现它在将来有用。

问题是网络摄像头在启动时会逐渐调整其亮度，因此您必须首先拍摄一些虚拟帧才能获得正常的图片......以下是我现在使用的内容：

var
 i : Integer;
...
begin
...
   for i := 0 to 24 do
   begin
     SendMessage(hand, WM_CAP_GRAB_FRAME, 0, 0);
     Sleep(200)
   end;
...
end;

像魅力一样，有点hacky，我希望设备也存在WaitForInputIdle函数......

为什么网络摄像头图像看起来比从其他应用程序启动时更暗？

1 个答案: