Wireless Video

[Qt Coder]

linking LIB files as dll solved my problem

I changed it as

LIBS += -lcv200.dll -lhighgui200.dll

also I needed to place the dll's where my qt project EXE resides.

Thanks to all who helped me.

[Qt Coder]

modifying

LIBS += -lcvl -lhighguil

to

LIBS += -lcv200.dll -lhighgui200.dll

solved my problem

also I had to place

1) libcv200.dll
2) libcvaux200.dll
3) libhighgui200.dll
4) libcxcore200.dll


above dll's in release folder where project exe resides


Thanx to all who helped me


My another question is if we attached webcam to a PC in LAN,can we access and view it in other PC using Qt?

[hatred]

hello, can i ask you something, i'm currently doing a similar program with yours, im trying to send a video feed from a mobile robot into my laptop using qt and open cv,

i also use the same source code that have tried to open the webcam in opencv using Qt,

but after compiling the QtOpenCV i got thsi eror messages:

1. collect2: ld returned 1 exit status

can u share help me to solve this error?

[Qt Coder]

Post error message,there must be some error message above this " 1. collect2: ld returned 1 exit status" .

[tbscope]

Can we access and view webcam on my PC which is attached to other PC in LAN using Qt

Of course you can. Create a little server on the pc having the webcam. Send it to all the other clients that are connected.

[Qt Coder]

I m able to create server and client,but my question is


1) How to send IplImage over socket?

2) How to use threads to handle more than one client requests?

[squidge]

You don't need to use threads to handle more than one client request. Use signals, slots and asynchronous methods instead.

You can transfer the image as binary data.

[Qt Coder]

I have tried

CvCapture * camera;
 IplImage * image;
  qint64 nWrite;
 
 image=cvQueryFrame(camera);
 nWrite = gtcpSocket->write((char*)image,sizeof(image));

CvCapture * camera;
 IplImage * image;
  qint64 nWrite;

 image=cvQueryFrame(camera);
 nWrite = gtcpSocket->write((char*)image,sizeof(image));

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But nWrite shows only 4 bytes transferred..

How to send image as binary data?

[squidge]

sizeof(image) is a pointer, so 4 bytes is what I'd expect it to write.

image->imageData may be more suitable (or wherever the data is stored)

[khrave]

hello, can i ask you something, i'm currently doing a similar program with yours, im trying to send a video feed from a mobile robot into my laptop using qt and open cv,

i also use the same source code that have tried to open the webcam in opencv using Qt,

but after compiling the QtOpenCV i got thsi eror messages:

1. collect2: ld returned 1 exit status

can u share help me to solve this error?

What I do in this situation is go into my project directory via console and run make from console. Usually, but not always, it will show some more info regarding why ld returned 1 exit status. More often than not, it is because a library wasn't found. Hope this helps!

[Qt Coder]

Hey I m able to send image over socket ,but at clients side I m not able to see any image

My server application code for sending image is

QImage pic("Viraat.png","PNG");
 
    QByteArray ba;
    QBuffer buffer( &ba );
    buffer.open(QIODevice::WriteOnly);
    pic.save(&buffer,"PNG");           // writes image into ba in PNG format
    nWrite = gtcpSocket->write((const char *)ba);
 
    QMessageBox::critical(this, QString::number(int(nWrite)),
                              tr("Size of Image sent to client: %1."));

QImage pic("Viraat.png","PNG");
   
    QByteArray ba;
    QBuffer buffer( &ba );
    buffer.open(QIODevice::WriteOnly);
    pic.save(&buffer,"PNG");           // writes image into ba in PNG format
    nWrite = gtcpSocket->write((const char *)ba);

    QMessageBox::critical(this, QString::number(int(nWrite)),
                              tr("Size of Image sent to client: %1."));

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here MessageBox shows that 8 bytes transferred which is the size of file.


Now at client side I have written code as

QDataStream in(tcpSocket);
       in.setVersion(QDataStream::Qt_4_6);
 
       QByteArray ba;
       QBuffer buffer( &ba );
       buffer.open(QIODevice::ReadOnly);
 
        //nRead = in.device()->read((char *)&ba,sizeof(ba));
       ba =  tcpSocket->read(100);
 
 
       //empty image
       QImage image(2048,1024,QImage::Format_Indexed8);
 
       //load pixel data into empty image from QByteArray
       image = QImage::fromData(ba,"PNG");
 
        //load pixel data into empty image from QByteArray
 
 
        QMessageBox::critical(this,tr("Data Received: %1."),QString::number(ba.length()));
        image.save("d:/pic.png","PNG");
        ui->label_3->setPixmap(QPixmap:: fromImage( QImage(image)));
        ui->label_3->show();
        tcpSocket->disconnectFromHost();

QDataStream in(tcpSocket);
       in.setVersion(QDataStream::Qt_4_6);
        
       QByteArray ba;
       QBuffer buffer( &ba );
       buffer.open(QIODevice::ReadOnly);
       
        //nRead = in.device()->read((char *)&ba,sizeof(ba));
       ba =  tcpSocket->read(100);


       //empty image
       QImage image(2048,1024,QImage::Format_Indexed8);

       //load pixel data into empty image from QByteArray
       image = QImage::fromData(ba,"PNG");

        //load pixel data into empty image from QByteArray
    

        QMessageBox::critical(this,tr("Data Received: %1."),QString::number(ba.length()));
        image.save("d:/pic.png","PNG");
        ui->label_3->setPixmap(QPixmap:: fromImage( QImage(image)));
        ui->label_3->show();
        tcpSocket->disconnectFromHost();

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but nothing is saved at D drive and no image is set in label. but it shows it received 8 bytes of data...

how to construct Qimage from raw data and how to save the data/image received over socket to local hard drive ?

[wysota]

You expect the whole image data to fit into 8 bytes? Or even into 100 bytes?

[Qt Coder]

I dont know how much would be the image size so I have given maximum of 100 bytes data to read. what to give read size otherwise if you dont know how much size of data is going to arrive on socket?

[squidge]

So why not send the size of the data your sending before sending the actual image data? Then you know the size you are expecting.

[Qt Coder]

I m able to receive data on socket but I need to construct image from it and set it as pixmap to my label

My client side code is

QPixmap pixmap;
      QDataStream in(tcpSocket);
       in.setVersion(QDataStream::Qt_4_6);
 
       QByteArray ba;
       QBuffer buffer( &ba );
       buffer.open(QIODevice::ReadOnly);
        ba =  tcpSocket->read(100);
 
        pixmap.loadFromData(ba,"PNG");
 
        ViewObj->ui.label->setPixmap(pixmap);

QPixmap pixmap;
      QDataStream in(tcpSocket);
       in.setVersion(QDataStream::Qt_4_6);
        
       QByteArray ba;
       QBuffer buffer( &ba );
       buffer.open(QIODevice::ReadOnly);
        ba =  tcpSocket->read(100);

        pixmap.loadFromData(ba,"PNG");

        ViewObj->ui.label->setPixmap(pixmap);

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But no image is displayed also tell me some way how to save received image on local hard drive

[wysota]

Please, answer these questions:

• How many bytes (roughly) would a BMP image with 2048x1024 size and an 8 bit colormap take?
• How many bytes are sent on the socket on the transmitting side?
• How many bytes should be sent on the socket assuming a maximal possible image compression available is about 1:12?
• How are those three figures related to each other?
• What is the size of byte array on the receiving end before calling loadFromData()?

If you don't know how to answer those questions, please look for answers in the Internet. Answers to the last two should give you a hint why an image is not displayed.

[Qt Coder]

Currently The image which I m sending is of
1)Image resolution - 128 by 128
2)format - "PNG"
3)size on disk - 8,192 bytes

but at server side it shows only 8 bytes transferred...

As I searched on internet 8 bit Grayscale means 1 byte per pixel

so answer to your first question is

1) 2048x1024 = 2097152 pixels which would mean 2097152 bytes
2) in my case only 8 bytes are sent on the socket on the transmitting side
3) if we consider above bmp image with the 2048*1024 resolution then 174762 bytes should be sent assuming a maximal possible image compression available is about 1:12

correct me if I m wrong

[wysota]

So what does it mean if 8 bytes are sent on the transmitting end if the image has volume of 8kB? Can the image be recreated on the receiving end from those 8 bytes?

[Qt Coder]

I m getting a runtime error in my server application

when I compile it it gives error

C:\Qt\2010.02.1\qt\examples\widgets\WebServer\debug\QtOpenCV.exe exited with code -1073741515

C:\Qt\2010.02.1\qt\examples\widgets\WebServer\debug\QtOpenCV.exe exited with code -1073741515

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it use to run fine before ,

I tried adding messegebox in main() at very first step but control dont even reaches there, if I run exe manually it gives

Runtime error !.. This application has requested the runtime to terminate it in an unusual way.

Runtime error !.. This application has requested the runtime to terminate it in an unusual way.

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I m not able to debug it also..

How to fix this runtime error?

[Qt Coder]

Hey I got where this runtime error lies

I need to place those OpenCV dll's in my debub folder.

Now my server side code is

QImage pic("monkey_off_128x128.png","PNG");   
 
    QByteArray ba;
    QBuffer buffer( &ba );
    buffer.open(QIODevice::WriteOnly);
    pic.save(&buffer,"PNG");           // writes image into ba in PNG format
    nWrite = gtcpSocket->write(ba.data());
    QMessageBox::critical(this, QString::number(ba.length()),QString::number((int)nWrite));

QImage pic("monkey_off_128x128.png","PNG");   

    QByteArray ba;
    QBuffer buffer( &ba );
    buffer.open(QIODevice::WriteOnly);
    pic.save(&buffer,"PNG");           // writes image into ba in PNG format
    nWrite = gtcpSocket->write(ba.data());
    QMessageBox::critical(this, QString::number(ba.length()),QString::number((int)nWrite));

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The messageBox shows ba.length() to be 9437 and nWrite to be 8 only.
where as the file size is 7045 bytes and size on disk 8192 bytes ,I dont know from where it has added extra bytes.

also why it sends only 8 bytes over socket?