C / C++ / MFC

10-Oct-11 23:02

Hello! I have a function that saves a jpeg file from an IP camera. It works sometimes, but sometimes, it doesnt. When I investigated, i found out that in the instances that it didnt work, the characters of the file when i convert it to a text file looks like this:

ෝ㚆��鍫᱉㓉��⛷통⌫㘿答窂脚麜鋴ᬓ犚厜褝沣놊��ꋂ᝚䴍㢛諱᷐锫잛䕡逺Řޥ舔룣⣅‵쭫帏갪ಱ彗䩂䖒깔숢⢞ᴑ鎵졋쮧呤ᑵ蛝㙕횇涚噈혘㙌๝සᲷ貚臛诞

Proper jpeg files have characters that look like this:

*456789:CDEFGHIJSTUVWXYZcdefghijstuvwxyzƒ„…†‡ˆ‰Š’“”•–—˜™š¢£¤¥¦§¨©ª²³

I don't know what's wrong. Please help me!!! Here is the function I'm using:

XML

int SendReceiveTest1( Socket^ server )
{
    FileStream^ ambot = File::Create("pastilan.jpg");
    array<Byte>^ msg = Encoding::UTF8->GetBytes("GET /snapshot.cgi HTTP/1.1\r\n");
    array<Byte>^ msg1 = Encoding::UTF8->GetBytes("Authorization: Basic YWRtaW46\r\n\r\n");
    array<Byte>^ header = gcnew array<Byte>(224);
    array<Byte>^ bytes = gcnew array<Byte>(30000);
    try
    {
      // Blocks until send returns.
    Int32 byteCount = server->Send( msg );
    Console::WriteLine( "Sent {0} bytes.", byteCount.ToString() );

    Int32 byteCount1 = server->Send( msg1 );
    Console::WriteLine( "Sent {0} bytes.", byteCount1.ToString() );

    byteCount = server->Receive( header, header->Length, SocketFlags::None );
    if ( byteCount > 0 )
    {
        Console::WriteLine( Encoding::UTF8->GetString( header ) );
    }

    while(byteCount > 0){
        byteCount = server->Receive( bytes, server->Available, SocketFlags::None);
    }

    ambot->Write( bytes, 0, bytes->Length );

    if( ambot )
        delete (IDisposable^)ambot;
    }
    catch ( SocketException^ e )
    {
        Console::WriteLine( "{0} Error code: {1}.", e->Message, e->ErrorCode.ToString() );
        return ( e->ErrorCode );
    }
    return 0;
}

Usually I dont bother asking if it NEVER works. But Im worried about this particular code because most of the time it DOES work. Thanks!!!

Richard MacCutchan11-Oct-11 0:10

11-Oct-11 0:10

JPEG files contain encoded image data and will make no sense whatsoever if displayed as text. You should investigate what is happening to your data in between receiving it from the camera and passing it to whatever location you do. I am not sure that you should be trying to encode the data as indicated in the code fragment above.

Unrequited desire is character building. OriginalGriff

Naniw11-Oct-11 1:08

11-Oct-11 1:08

Im sorry, something went wrong, here's the whole function:

int SendReceiveTest1( Socket^ server )
{
FileStream^ ambot = File::Create("pastilan.jpg");
array<Byte>^ msg = Encoding::UTF8->GetBytes("GET /snapshot.cgi HTTP/1.1\r\n");
array<Byte>^ msg1 = Encoding::UTF8->GetBytes("Authorization: Basic YWRtaW46\r\n\r\n");
array<Byte>^ header = gcnew array<Byte>(224);
array<Byte>^ bytes = gcnew array<Byte>(30000);
try
{
// Blocks until send returns.
Int32 byteCount = server->Send( msg );
Console::WriteLine( "Sent {0} bytes.", byteCount.ToString() );

Int32 byteCount1 = server->Send( msg1 );
Console::WriteLine( "Sent {0} bytes.", byteCount1.ToString() );

byteCount = server->Receive( header, header->Length, SocketFlags::None );
if ( byteCount > 0 )
{
Console::WriteLine( Encoding::UTF8->GetString( header ) );
}

while(byteCount > 0){
byteCount = server->Receive( bytes, bytes->Length, SocketFlags::None);
}

ambot->Write( bytes, 0, bytes->Length );

if( ambot )
delete (IDisposable^)ambot;
}
catch ( SocketException^ e )
{
Console::WriteLine( "{0} Error code: {1}.", e->Message, e->ErrorCode.ToString() );
return ( e->ErrorCode );
}
return 0;
}

The pastilan.jpg file that results is sometimes a proper jpeg file, meaning it's really a snapshot of the ip camera, and sometimes, it's not. It's totally RANDOM. I don't know what's happening...

Richard MacCutchan11-Oct-11 5:21

11-Oct-11 5:21

C++

while(byteCount > 0){
     byteCount = server->Receive( bytes, bytes->Length, SocketFlags::None);
}

ambot->Write( bytes, 0, bytes->Length );

In the above lines you may be overwriting part of your image in the while loop, which means that you only write the last part of the file. You are also using the buffer length rather than the actual bytecount to write to the destination file.

Unrequited desire is character building. OriginalGriff

Luc Pattyn11-Oct-11 6:03

Luc Pattyn

11-Oct-11 6:03

There are two major flaws AFAICT:

1. you have a receiving loop that overwrites the receiving buffer, whereas your file writing is outside the loop; the correct way would have both receive and write in one loop, there is no need to first hold the entire image in memory.

2. you write a fixed length, independent of what you received. That is so wrong; your write statement needs to be based on the byte count you obtain from the receive statement.

And there is another weakness, if not a bug: you assume the header will hold 224 bytes. What if it doesn't? It is not up to the client to guess how big a header the server will use. Check the standards, or use an official implementation (if this is managed C++, why not use HttpWebRequest/HttpWebResponse classes?).

Smile | :)

PS: please learn how to apply proper formatting, using PRE tags[^].

Luc Pattyn [My Articles] Nil Volentibus Arduum
iSad

modified 11-Oct-11 12:27pm.

Message Removed

11-Oct-11 16:29

11-Oct-11 16:29

Message Removed

Luc Pattyn11-Oct-11 16:33

Luc Pattyn

11-Oct-11 16:33

Please edit the above message and use PRE tags, so I can look at it tomorrow.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum
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Naniw11-Oct-11 16:38

11-Oct-11 16:38

Sorry about that...

C++

int SendReceiveTest2( Socket^ server )
{
     FileStream^ ambot = File::Open("pastilan.jpg", FileMode::Create, FileAccess::ReadWrite);
     array<Byte>^ msg = Encoding::ASCII->GetBytes("GET /snapshot.cgi HTTP/1.1\r\n");
     array<Byte>^ msg1 = Encoding::ASCII->GetBytes("Authorization: Basic YWRtaW46\r\n\r\n");
     array<Byte>^ header = gcnew array<Byte>(224);
     array<Byte>^ bites = gcnew array<Byte>(1);
     try
     {
         // Blocks until send returns.
     int byteCount = server->Send( msg );
      Console::WriteLine( "Sent {0} bytes.", byteCount.ToString() );
 
     int byteCount1 = server->Send( msg1 );
      Console::WriteLine( "Sent {0} bytes.", byteCount1.ToString() );
 
     byteCount = server->Receive( header, header->Length, SocketFlags::None );
      if ( byteCount > 0 )
      {
          Console::WriteLine( Encoding::UTF8->GetString( header ) );
      }
 
     int count = 0;
     while(1){
          byteCount = server->Receive( bites );
          ambot->Write(bites,0,1);
          if (byteCount ==   0)
               break;
     }
 
     if( ambot )
          delete (IDisposable^)ambot;
     }
     catch ( SocketException^ e )
     {
          Console::WriteLine( "{0} Error code: {1}.", e->Message, e->ErrorCode.ToString() );
          return ( e->ErrorCode );
     }
     return 0;
}

Luc Pattyn11-Oct-11 22:33

Luc Pattyn

11-Oct-11 22:33

oh my.

1.
you could have edited the existing message to adapt its formatting, rather than create yet another one, there is an edit widget below each of your posts for you to do so.

2.
when I said you needed to receive and store in a loop, and use the right amount of bytes, I did not imply to deal with one byte at a time; rather something like:

for(;;) {
    byteCount = server->Receive( bytes, bytes->Length, SocketFlags::None);
    if (byteCount<=0) break;
    ambot->Write( bytes, 0, byteCount );    // <<<< here we store what we've got, and nothing more.
}

The performance difference should be quite noticeable.

3.
I'm still not sure about your header, which you are basically swallowing (i.e. showing as if it were text?????, then forgetting). Is it part of the communication, or is it the header part of the image (which you would need to include in the file)?
And is the camera emitting a JPEG format? Most camera's do, if so the very first bytes are likely to be FF D8 FF (these are three bytes represented in hex, not as text characters!), and most likely the bytes 6 through 9 contain 4A 46 49 46.
So check the incoming data (including your "header") for these values: either use a hex editor to see your resulting JPEG file, or adapt your code so you can see the first 10 bytes (in hex) for both the header and the first (or every) data packet you receive. Alternatively, try your code without the receive-and-show-header statements.
OTOH, if the camera does not generate JPEG, storing some other format into a file and give that a JPEG extension is not the way to convert image formats!

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum
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Naniw11-Oct-11 1:10

11-Oct-11 1:10

Oh, by the way, i just displayed the two sets of (jibberish) characters to demonstrate the difference in encoded data that results. The proper set of characters is the second one. I don't know where the first one comes from.

image processing toolkits | batch image processing

C^hris L^osinger11-Oct-11 3:35

C^hris L^osinger

11-Oct-11 3:35

Member 8250612 wrote:
Proper jpeg files have characters that look like this:

*456789:CDEFGHIJSTUVWXYZcdefghijstuvwxyzƒ„…†‡ˆ‰Š’“”•–—˜™š¢£¤¥¦§¨©ª²³

no, they don't.

well, let me rephrase that: nothing in the JPEG spec requires such a sequence of bytes. you might get an image which encodes to that, but that's entirely coincidental.

the most you can say about a JPEG is that it probably starts with these three bytes: FFD8FF. beyond that, the only constant is the structure defined by the file format; and that works with little four-byte headers which precede the various blocks of data and none of those blocks is required to look like that.

modified 11-Oct-11 15:58pm.

Setting a bmp as a window background

David Crow11-Oct-11 4:07

David Crow

11-Oct-11 4:07

Have you tried asking this question in the Managed C++ forum?

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jkirkerx10-Oct-11 13:40

10-Oct-11 13:40

I've been trying to make my Window pretty or appealing, by setting a bitmap in the background of the window. The information I have found is mostly just do this, and it works, I came up with this, and placed it in my WM_PAINT. At first I got a little TT logo at the upper left, then it went away, I thought it was going to work.

I have triple checked my IDB_BG_INSTALL_PANE_BMP, and I know I got that right.

//Bitmap Variables
	HDC						mem_DCInstallation;
	HBITMAP					bmp_BGInstallation;

	hdc = BeginPaint(cWnd, &ps);
	
	//////////////////////////////////////////////////////////////////////////////////////////
	//Setup the Windows Background First
	bmp_BGInstallation = LoadBitmap(hIIS_Instance, MAKEINTRESOURCE( IDB_BG_INSTALL_PANE_BMP ));
		mem_DCInstallation = CreateCompatibleDC(hdc);
	
		SelectObject(mem_DCInstallation, bmp_BGInstallation);
		BOOL bbResult;
		bbResult = BitBlt(hdc, 0, 0, 500, 311, mem_DCInstallation, 0, 0, SRCCOPY);

		// Release the Bitmap Image
		DeleteDC(mem_DCInstallation);
	DeleteObject(bmp_BGInstallation);
	//////////////////////////////////////////////////////////////////////////////////////////

TheGreatAndPowerfulOz10-Oct-11 14:45

TheGreatAndPowerfulOz

10-Oct-11 14:45

Do your background bitmap painting by handling the WM_ERASEBACKGROUND[^] message

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jkirkerx10-Oct-11 16:01

10-Oct-11 16:01

So I want to paint in that message event?, or just add it and put the return TRUE or FALSE?

jkirkerx10-Oct-11 16:14

10-Oct-11 16:14

OK, I get it,I mad the WM_ERASEBKGND return 1, doesn't seem to matter yet what I set it to, and fixed the code I posted. I messed it up from trial and error, and left off at error.

This is the correct code

//////////////////////////////////////////////////////////////////////////////////////////
    //Setup the Windows Background First
    bmp_BGInstallation = LoadBitmap(hIIS_Instance, MAKEINTRESOURCE(IDB_BG_INSTALL_PANE_BMP));
    mem_DCInstallation = CreateCompatibleDC(hdc);

    SelectObject(mem_DCInstallation, bmp_BGInstallation);
    BitBlt(hdc, 0, 0, 504, 331, mem_DCInstallation, 0, 0, SRCCOPY);

    // Release the Bitmap Image
    DeleteDC(mem_DCInstallation);
    DeleteObject(bmp_BGInstallation);
    //////////////////////////////////////////////////////////////////////////////////////////

Thanks for pointing out the WM event, I remember reading it somewhere earlier, but forgot about it.

Say, 1 more question, if I create a larger bitmap of the same image, would windows automatically size it down, so I can resize the window larger, without losing image quality?

Richard MacCutchan10-Oct-11 22:15

10-Oct-11 22:15

jkirkerx wrote:
if I create a larger bitmap

In that case you would probably need to use StretchBlt()[^].

Unrequited desire is character building. OriginalGriff

jkirkerx11-Oct-11 7:01

11-Oct-11 7:01

It took me awhile to understand the process, but as a by product, I learned how to create regions in the window, and paint them, and they work in the resize event as well.

I'll try the above suggestion first, before trying the below dll integration.

Thanks for the help, the information is out there, but I'm not using the right words to find it.

Richard MacCutchan11-Oct-11 7:43

11-Oct-11 7:43

jkirkerx wrote:
the information is out there, but I'm not using the right words to find it.

Sure, this is a fairly obscure part of Windows programming, most people just use the default background. But, it sounds like you are getting there.

Unrequited desire is character building. OriginalGriff

jkirkerx11-Oct-11 8:41