image not getting refreshed in Qlabel

[stampede]

Yes but why do you need disk access ? Worker can process the image and send the processed result directly to the display thread, what's wrong with that
now you have this:

[load image from disk] --> process it --> [save to disk] --> inform gui that image is updated --> [load from disk] --> display

[load image from disk] --> process it --> [save to disk] --> inform gui that image is updated --> [load from disk] --> display

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why not have this:

[load image from disk] --> process it -->  inform gui that image is updated, send the image via signal --> display

[load image from disk] --> process it -->  inform gui that image is updated, send the image via signal --> display

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[prkhr4u]

Can you pl tell how to pass image via signal,I am unable to do so.

[anda_skoa]

You add QImage as a parameter of the signal

class GrabThread : public QThread
{
    Q_OBJECT
 
signals:
    void ImageRefreshSignal(const QImage &image);
};

class GrabThread : public QThread
{
    Q_OBJECT

signals:
    void ImageRefreshSignal(const QImage &image);
};

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And you pass the image at emit

emit ImageRefreshSignal(image); // or image.copy() if the thread continues to use "image"

emit ImageRefreshSignal(image); // or image.copy() if the thread continues to use "image"

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Similar signature changes to slot and connect obviously

Cheers,
_

[prkhr4u]

I have done the changes and now am sending the image via signal,but still I am unable to refresh the image.
Here is what I have done:

class GrabThread : public QThread
{
    Q_OBJECT
     private:
      void run();
    public:
    signals:
    void ImageRefreshSignal(const QImage &image);
};

class GrabThread : public QThread
{
    Q_OBJECT
     private:
      void run();
    public:
    signals:
    void ImageRefreshSignal(const QImage &image);
};

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Signal emmited like:

QImage img;
img.load("abc.bmp");
emit ImageRefreshSignal(img);

QImage img;
img.load("abc.bmp");
emit ImageRefreshSignal(img);

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slot method called like:

void Dialog_user::ImageRefreshSlot(QImage img )
{
    qDebug()<<"inside slot";    
    ui->label->setPixmap(QPixmap::fromImage(img));
}

void Dialog_user::ImageRefreshSlot(QImage img )
{
    qDebug()<<"inside slot";    
    ui->label->setPixmap(QPixmap::fromImage(img));
}

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//dialog_user.h

class Dialog_user : public QDialog
{
    Q_OBJECT
 
public:
    explicit Dialog_user(QWidget *parent = 0);
    ~Dialog_user();
 
private slots:
    void ImageRefreshSlot (QImage img);

class Dialog_user : public QDialog
{
    Q_OBJECT
    
public:
    explicit Dialog_user(QWidget *parent = 0);
    ~Dialog_user();
    
private slots:
    void ImageRefreshSlot (QImage img);

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the connection is as follows:

QObject::connect( & gthread, SIGNAL( ImageRefreshSignal(QImage) ),& d_user, SLOT( ImageRefreshSlot(QImage) ) );

QObject::connect( & gthread, SIGNAL( ImageRefreshSignal(QImage) ),& d_user, SLOT( ImageRefreshSlot(QImage) ) );

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I have checked the mechanism, and the message "inside slot" is being printed,but the image is not getting refreshed.

[stampede]

Why do you load the image before sending it ? Can't you send the processed object ? Can we see the image processing code ?

[prkhr4u]

I have a separate image processing thread,which processes the image object as well as writes it to a bmp file "abc.bmp"
The image processing is entirely different from GUI thread and works continuously in the background.
As the GUI thread is only meant for display purposes,I am not sending the processed object for writing in GUI thread.

Is there other way to send the image via a signal without loading it?

[stampede]

I have a separate image processing thread,which processes the image object as well as writes it to a bmp file "abc.bmp"
The image processing is entirely different from GUI thread and works continuously in the background.
As the GUI thread is only meant for display purposes,I am not sending the processed object for writing in GUI thread.

Yes we know that ! Show us the code where you do this "abc.bmp" file writing in image processing thread. We want you to just emit the changed image apart from writing it to file. You have some image object on which you call save() method, right ? Just emit a signal, passing this object as parameter...

[prkhr4u]

Here is the main code for writing:

void convert2bmp(unsigned int **Buffer_in,unsigned int x_size,unsigned int y_size,char *output_str)
unsigned char* data3d = new unsigned char[x_size*y_size];
fp = fopen (output_str, "wb");
    for ( i = x_size; i >= 0; i--)
        for (j = 0; j < y_size; j++)
        {            
            data3d[k++]=Buffer_in[i][j];
        }
    fwrite( data3d, sizeof( char ),x_size*y_size, fp);
    fclose(fp);

void convert2bmp(unsigned int **Buffer_in,unsigned int x_size,unsigned int y_size,char *output_str)
unsigned char* data3d = new unsigned char[x_size*y_size];
fp = fopen (output_str, "wb");
    for ( i = x_size; i >= 0; i--)
        for (j = 0; j < y_size; j++)
        {            
            data3d[k++]=Buffer_in[i][j];
        }
    fwrite( data3d, sizeof( char ),x_size*y_size, fp);
    fclose(fp);

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Buffer_in: buffer containing the processed image data
x_size,y_size: dimension of image
Output_str: name of output file:"abc.bmp"

After some image processing,which occurs on the buffer,I am writing it to a bitmap file.The Buffer_in is only available to me inside this(image processing thread) and then I am displaying the image in a Qlabel in GUI thread.
The method "convert2bmp" is being called after every image processing iteration and the processed image needs to be displayed on a GUI thread everytime.
But the image is not getting refreshed every time.

[ChrisW67]

The variable k is used uninitialised.

Just from looking at what you are doing to the image data I think it is exceptionally unlikely you have a valid BMP at the end of the process.
Ignoring your GUI for a moment. Is the BMP file being written? Is it the correct size in bytes? Is it a valid BMP and can you see the right image in Microsoft Paint or something similar?

[prkhr4u]

The bmp file is being written properly.
I have excluded the code for bmp header and small variables like i,j,k.
The code for main file writing is being enclosed.

[anda_skoa]

If Buffer_in is your pixel data, you can probably use it to create a QImage instance pointing to the same image data.

And then use QImage::copy() to send it through the signal.

Cheers,
_

[prkhr4u]

I have sent the pixel data using QImage as follows:

QImage myImage(400,700,QImage::Format_RGB888);
                                   for (int x=0;x<400;x++)
                                       for (int y=0;y<700;y++)
                                           myImage.setPixel(x,y,qRgb(Buffer_in[y][x*3],Buffer_in[y][x*3+1],Buffer_in[y][x*3+2]));                                   
                                   emit ImageRefreshSignal(myImage.copy(0,0,400,700));

QImage myImage(400,700,QImage::Format_RGB888);
                                   for (int x=0;x<400;x++)
                                       for (int y=0;y<700;y++)
                                           myImage.setPixel(x,y,qRgb(Buffer_in[y][x*3],Buffer_in[y][x*3+1],Buffer_in[y][x*3+2]));                                   
                                   emit ImageRefreshSignal(myImage.copy(0,0,400,700));

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and used the slot as follows:

void Dialog_user::ImageRefreshSlot(QImage img )
{
    qDebug()<<"inside slot";   
    ui->label->setPixmap(QPixmap::fromImage(img));
}

void Dialog_user::ImageRefreshSlot(QImage img )
{
    qDebug()<<"inside slot";   
    ui->label->setPixmap(QPixmap::fromImage(img));
}

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still the label containg the image is not getting refreshed.
The slot is being called correctly and the debug message "Inside slot" is being printed.