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Getting a snapshot from a webcam with Delphi

Answer 1

A:

I use a component called TVideoCap. It is for 3, 4, and 5 but it includes source so it is easy to update. It will do exactly what you want. Just do a search for 'TVideoCap'.

David 2010-08-11 03:48:12

Thanks, I'll check it out. Do you have any EXE that you have produced using this unit that you can give me that works - I just want to verify that there is nothing inherently wrong with my system. R

2010-08-11 04:09:03

Hi David, I downloaded VideoCap and installed a real Webcam - my results are the same as in the previous answer above - now that I have a real webcam, then I try to connect to a driver the dialog opens asking me to select the source, but the connect fails anyway

2010-08-13 03:15:29

Answer 2

+3 A:

Your program works for me on Win7 32bits with D2010.

What it does though is raising an exception:

---------------------------
Project WebCamTest.exe raised exception class EFCreateError with message 
'Cannot create file "c:\webcam.jpg". Access is denied'.
---------------------------

which can be corrected by changing

FJpeg.SaveToFile('c:\webcam.jpg');

to

FJpeg.SaveToFile(TPath.GetTempPath + '\webcam.jpg');

And also, it does not display the whole available image, you'd have to enlarge your Panel, recenter or shrink the webcam output.

Update with some code modifications that would make it work per your comments...

  // introducing the RGB array and a buffer
  TVideoArray = array[1..PICHEIGHT] of array[1..PICWIDTH] of TRGBTriple;
  PVideoArray = ^TVideoArray;

  TForm1 = class(TForm)
[...]
  FBuf24_1: TVideoArray;
[...]

function FrameCallbackFunction(AHandle: hWnd; VIDEOHDR: TVideoHDRPtr): bool; stdcall;
var
  I: integer;
begin
  result:= true;

  with form1 do begin
  try
    if ConvertCodecToRGB(FCodec, VideoHDR^.lpData, @FBuf2, PICWIDTH, PICHEIGHT) then
    begin
      for I:= 1 to PICHEIGHT do FBuf1[I]:= FBuf2[PICHEIGHT- (I- 1)];
      SetBitmapBits(FBitmap.Handle, PICWIDTH* PICHEIGHT* SizeOf(DWord), @FBuf1);
    end
    else
    begin  // assume RGB
      for I:= 1 to PICHEIGHT do
        FBuf24_1[I] := PVideoArray(VideoHDR^.lpData)^[PICHEIGHT-I+1];
      SetBitmapBits(FBitmap.Handle, PICWIDTH* PICHEIGHT* SizeOf(RGBTriple), @FBuf24_1);
    end;
[...]

François 2010-08-11 06:01:33

On my system, the message results I get are: WM_CAP_DRIVER_CONNECTMsgResult = false WM_CAP_SET_PREVIEWRATEMsgResult = true WM_CAP_SET_OVERLAYMsgResult = false WM_CAP_SET_PREVIEWMsgResult = false WM_CAP_SET_CALLBACK_FRAMEMsgResult = true WM_CAP_GRAB_FRAME_NOSTOPMsgResult = false and FrameCallbackFunction never fires. It looks as if it is failing to connect.

2010-08-12 15:42:31

Clearly you cannot connect to the webcam. Have you tried with a capture driver other than 0? It can be from 0 to 9. Maybe you have more than 1 and the webcam is not the index 0?`MsgResult := SendMessage(FCapHandle, WM_CAP_DRIVER_CONNECT, x, 0);`

François 2010-08-12 17:20:09

Thanks François. At present I don't have any webcams - just a simulator. The simulator seems to go in that Skype can see the "camera" OK. I tried calling SendMessage(FCapHandle, WM_CAP_DRIVER_CONNECT, x, 0); with x = 0 through 9 and they all returned false. Incidentally - how were you able to format the text as code in the comment?

2010-08-12 22:34:31

Update - I installed a real webcam. Now, when I execute the SendMessage(FCapHandle, WM_CAP_DRIVER_CONNECT, 0, 0) ; a dialog pops up asking me to select the video capture source. The drop-down only has one entry in it - for the Logitech webcam. When I select this however, I still get the same failure result (false) from SendMessage(FCapHandle, WM_CAP_DRIVER_CONNECT, 0, 0) ;.

2010-08-13 03:11:06

Hey François, I am tantalizingly close. With a real webcam connected, I can get 1 second snapshots displaying on the panel. Problem is, I need programmatic access to the image. The JPEG file saved is all black. I have tried several other variants of the example code off the web and they all work, but the jpeg is blank. Any ideas?

2010-08-16 23:51:45

Time to learn some debugging... ;-) Your function `ConvertCodecToRGB` returns a `Boolean` status if it converted OK or not. You should test it. You'd find it failed because the Codec it is passed (probably in your case also) is a `vcRGB` which falls in the `case else` where nothing is done. And BTW to embed code in comments, use the back quote ```

François 2010-08-17 00:54:44

Correct. So "vcRGB" is returned by the routine BICompressionToVideoCodec. How should I handle that case value?

2010-08-17 19:56:08

I'm really not familiar with all that, but I guess that in this case you might not need to convert the pixels format, just have to pass them in the proper order to the destination...

François 2010-08-17 21:28:15

I found this comment: `"The problem with all black or white images comes from the fact that ConvertCodecToRGB doesn't handle case where the codec is running in RGB (vcRGB) mode. In this case you need to change the bitmap from 32 to 24 bit mode and copy the data from the source buffer to the dest buffer unchanged. Remember that the MOVE in Delphi is limited to an INTEGER for the move size."which does suggest something along the lines of what you are suggesting. I'm not sure how the data is arranged in the buffer - the size is reported as 304128 (=640x480) suggesting one byte per pixel?

2010-08-17 21:45:01

Aha. 640x480 is not 304128. Close but not close enough. The structure BitmapInfo after the call to SendMessage(FCapHandle, WM_CAP_GET_VIDEOFORMAT, SizeOf(BitmapInfo), Integer(@BitmapInfo)) has the values Width=352, Height=288, BitCount=24, so I conclude it's 3 bytes per pixel: 352x288x3 = 304128. Now presumably I need to get this data into the destination buffer?

2010-08-17 22:15:20

That would make sense for RGB: 3 bytes, 1 per color, total 24 bits. Now you have to find in what order they come and where to put them in the dest buffer.

François 2010-08-18 00:18:33

See my update. These code changes do the trick... And for me it works with 640x480 BTW.

François 2010-08-18 01:44:04

Brilliant. I'd almost got to the same point (my image is still upside down!). Many thanks, R.

2010-08-18 02:56:51

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Getting a snapshot from a webcam with Delphi

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