Receiving raw image data through TCP for display using Qt

[anda_skoa]

However the image I get is not totally black (It should be all black as I am not providing any light to the sensor). There are always some pixels with different color at the right bottom of the image (Refer attachment "temp1.png"). Can it be the noise?

Have you checked the return value of readRawData()? Is it the number of bytes you expect?

Cheers,
_

[yeye_olive]

You cannnot expect to read all the image data from the socket in one go. As already said in this thread, you must keep track of how much data you have received. My previous post outlines a solution to your problem that does not assume any single piece of data (including the 32-bit integers) to be read in a single execution of the slot connected to readyRead().

[benz6699]

Have you checked the return value of readRawData()? Is it the number of bytes you expect?

Cheers,
_

Yes, I have checked the return value of readRawData(). It is the number of bytes I expect. For this testing I have set the camera so that it deliver only 8 x 10 pixel image. And all the values in the buffer are zero from buffer[0] to buffer[79]. So I should get a total black image right? However I always get an image with pixels with other colour at the bottom right corner. I cannot identify where is my mistake here. Please advice.

[yeye_olive]

What value does QImage::byteCount() return? Scanlines must be 32-bit aligned, which generally introduces some padding; though there shouldn't be any if your image is 8 pixels wide and 8 bits deep.

By the way, you do not need to go through a temporary buffer. Just read into QImage::bits() directly.

[benz6699]

What value does QImage::byteCount() return? Scanlines must be 32-bit aligned, which generally introduces some padding; though there shouldn't be any if your image is 8 pixels wide and 8 bits deep.

By the way, you do not need to go through a temporary buffer. Just read into QImage::bits() directly.

QImage::byteCount() return the value I expect which is 80 (I "ask" the sensor to send me 8 x 10 x1 byte image). So what else can I check more?

Can you show me the code of how to read data directly into QImage::bits()? Thanks.

[yeye_olive]

QImage::byteCount() return the value I expect which is 80 (I "ask" the sensor to send me 8 x 10 x1 byte image). So what else can I check more?

Could you post a minimal complete example reproducing the problem?

Can you show me the code of how to read data directly into QImage::bits()? Thanks.

Sure, something like: result = my_qiodevice_ptr->read(my_qimage.bits() + number_of_bytes_already_read, my_qimage.byteCount() - number_of_bytes_already_read);

[benz6699]

Could you post a minimal complete example reproducing the problem?

#include "client.h"
#include <QHostAddress>
#include "mainwindow.h"
#include <QtGui>
#include <QAbstractSocket>
#include <QImage>
 
Client::Client(QWidget *parent) :
    QWidget(parent)
{
    socket = new QTcpSocket(this);  
    connect(socket, SIGNAL(readyRead()),this, SLOT(tcpReady()) );
}
 
int Client::capture(int mode, int NBRLine)
{
    if (socket->state() != QTcpSocket::ConnectedState)
    {
        socket->connectToHost("192.168.0.65", 1096);
    }
    /* send command to retrieve raw image data from sensor */
    if(socket->waitForConnected(5000))
    {
        QByteArray block;
        QDataStream out(&block, QIODevice::WriteOnly);
        out.setVersion(QDataStream::Qt_4_0);
        out.setByteOrder(QDataStream::LittleEndian);
        //out << qint32(0) << qint32(0) << qint32(0) << qint32(1);
        out << qint32(9) << qint32(1) << qint32(0) << mode << qint32(10) << qint32(2) << qint32(0) << NBRLine ;
        socket->write(block);
        socket->flush();
    }
    else
    {
        return false;
    }
}
 
 
int Client::tcpReady()
{
    QDataStream input(socket);
    input.setVersion(QDataStream::Qt_4_0);
    input.setByteOrder(QDataStream::LittleEndian);
    qint32 cmdID, counter, metaSize, CmdNbr, min, max, value, error, width, height;
    QByteArray buffer;
 
    int sizereceived = 0;
    int sizeAvailable = 0;
 
    forever{
        if (socket->bytesAvailable() < sizeof(qint32))
        {
            return 0;
        }
        input >> cmdID;
        // We get the data response with cmdID = 100 when we send a command to get parameter value
        if (cmdID == 100)
        {
            input >> counter >> metaSize >> CmdNbr >> min >>  max >> value;
        }
        // We get the data response with cmdID = 101 when we send a command to set parameter value
        else if (cmdID == 101)
        {
            input >> counter >> metaSize >> CmdNbr >> error;
        }
        // Here we get a streaming raw image data
        else if (cmdID == 1)
        {
            break;
        }
        else
        {
            return 0;
        }
    }
 
    // Here we read the data and construct image
    input >> counter >> metaSize >> width >> height; 
    int pixel = width * height;
    char *temp = new char[pixel];
    //char *temp = 0;
    int read = input.readRawData(temp, pixel);
    buffer.append(temp, pixel);
    QImage image = QImage(width, height, QImage::Format_Indexed8);
    delete [] temp;
 
    int m_index = 0;
    for (int i = 0; i < (pixel-1); ++i, ++m_index)
    {
        image.bits()[m_index] = buffer[i];
    }
    int cnt = image.byteCount();
    bool gray =  image.isGrayscale();
 
   if( !image.isNull() )
   {
      int result = image.save("E:/temp1.png", "PNG",1);
   }
    return 1;
}

#include "client.h"
#include <QHostAddress>
#include "mainwindow.h"
#include <QtGui>
#include <QAbstractSocket>
#include <QImage>

Client::Client(QWidget *parent) :
    QWidget(parent)
{
    socket = new QTcpSocket(this);  
    connect(socket, SIGNAL(readyRead()),this, SLOT(tcpReady()) );
}

int Client::capture(int mode, int NBRLine)
{
    if (socket->state() != QTcpSocket::ConnectedState)
    {
        socket->connectToHost("192.168.0.65", 1096);
    }
    /* send command to retrieve raw image data from sensor */
    if(socket->waitForConnected(5000))
    {
        QByteArray block;
        QDataStream out(&block, QIODevice::WriteOnly);
        out.setVersion(QDataStream::Qt_4_0);
        out.setByteOrder(QDataStream::LittleEndian);
        //out << qint32(0) << qint32(0) << qint32(0) << qint32(1);
        out << qint32(9) << qint32(1) << qint32(0) << mode << qint32(10) << qint32(2) << qint32(0) << NBRLine ;
        socket->write(block);
        socket->flush();
    }
    else
    {
        return false;
    }
}


int Client::tcpReady()
{
    QDataStream input(socket);
    input.setVersion(QDataStream::Qt_4_0);
    input.setByteOrder(QDataStream::LittleEndian);
    qint32 cmdID, counter, metaSize, CmdNbr, min, max, value, error, width, height;
    QByteArray buffer;

    int sizereceived = 0;
    int sizeAvailable = 0;

    forever{
        if (socket->bytesAvailable() < sizeof(qint32))
        {
            return 0;
        }
        input >> cmdID;
        // We get the data response with cmdID = 100 when we send a command to get parameter value
        if (cmdID == 100)
        {
            input >> counter >> metaSize >> CmdNbr >> min >>  max >> value;
        }
        // We get the data response with cmdID = 101 when we send a command to set parameter value
        else if (cmdID == 101)
        {
            input >> counter >> metaSize >> CmdNbr >> error;
        }
        // Here we get a streaming raw image data
        else if (cmdID == 1)
        {
            break;
        }
        else
        {
            return 0;
        }
    }

    // Here we read the data and construct image
    input >> counter >> metaSize >> width >> height; 
    int pixel = width * height;
    char *temp = new char[pixel];
    //char *temp = 0;
    int read = input.readRawData(temp, pixel);
    buffer.append(temp, pixel);
    QImage image = QImage(width, height, QImage::Format_Indexed8);
    delete [] temp;

    int m_index = 0;
    for (int i = 0; i < (pixel-1); ++i, ++m_index)
    {
        image.bits()[m_index] = buffer[i];
    }
    int cnt = image.byteCount();
    bool gray =  image.isGrayscale();

   if( !image.isNull() )
   {
      int result = image.save("E:/temp1.png", "PNG",1);
   }
    return 1;
}

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Sure, something like: result = my_qiodevice_ptr->read(my_qimage.bits() + number_of_bytes_already_read, my_qimage.byteCount() - number_of_bytes_already_read);

I tried the following code, but it give me the error message" :-1: error: C2664: 'qint64 QIODevice::read(char *,qint64)' : cannot convert parameter 1 from 'uchar *' to 'char *' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast."

input >> counter >> metaSize >> width >> height; 
int pixel = width * height;
 
QImage image = QImage(width, height, QImage::Format_Indexed8);
socket->read(image.bits(), pixel);

input >> counter >> metaSize >> width >> height; 
int pixel = width * height;

QImage image = QImage(width, height, QImage::Format_Indexed8);
socket->read(image.bits(), pixel);

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