problem with QImage function

[hardikgarg19]

Hello,
I am grabbing a frame from the camera and trying to save it. I am not getting the proper image. There are tiles in the image: example: if I take a picture of a pen, in the top 1/4th part of the saved image I can see 3 pens from left to right and rest of the image is black.
Below is the code:

int frmSize;
unsigned char *frameData=NULL;

//ISG_GetFrame syntax: ISG_GetFrame(int cameraNumber, unsigned char **frameData, int *frameSize)
/*Parametes:
int camNum - value 0 to n used to select one of multiple cameras available. In the case
of a single camera connection, value 0 should be used.
unsigned char **frameData - pass the address location of the pointer that will be used to reference
the returned image.
int frameSize - takes the address of an integer that will hold the number of bytes in the image
Return value:
int status - returns 0 on success, -1 on timeout waiting for an available frame/

ISG_GetFrame(camNum,&frameData,&frmSize);


QImage img(frameData,1920,1200,QImage::Format_Mono);
ISG_ReleaseFrame(camNum);
//img=img.convertToFormat(QImage::Format_RGB16);
img.save( "C:\\test_folder\\fileTEST20.JPG" );

I have checked that the camera is returning MONO8 image with width 1920 and height 1200

Please help me with this issue. Thank You

[Christian Ehrlicher]

And what's your exact problem now?
See ctor documentation: "The buffer must remain valid throughout the life of the QImage..."

[hardikgarg19]

@Christian-Ehrlicher Hello Christian,
The buffer is valid till it is converted to QImage. Now the problem is that, I am trying to display QImage on QGraphicsview as a video and I am missing some frames. Below is the function that I am using:

void MainWindow::whenNewFrame(const QImage& im)
{
QPixmap stream_pix=QPixmap::fromImage(im);
if (!stream_pix.isNull())
{
delete ui->graphicsView->scene();
ui->graphicsView->setScene(new QGraphicsScene(ui->graphicsView));
ui->graphicsView->scene()->addPixmap(stream_pix);
}
}

So, I want to know if there is anything I can do to speed up the process.

[Christian Ehrlicher]

Not deleting the QGraphicsScene and QGraphicsPixmapItem on every call to whenNewFrame will be a good starting point...

[hardikgarg19]

@Christian-Ehrlicher if I remove the delete ui->graphicsView->scene() from the code then I got an error "QImage: out of memory, returning null image". I have read that addPixmap(stream_pix) will return a pointer to QGraphicsPixmapItem and I can update it instead of adding and deleting scene every time. But, I am not sure how to do that.

[Christian Ehrlicher]

@hardikgarg19 said in problem with QImage function:

But, I am not sure how to do that.

As member of the class for example.

[hardikgarg19]

@Christian-Ehrlicher
I am able to solve the problem using setPixmap() function. Below is the code:

mainwindow.h

QGraphicsPixmapItem *Item;

mainwindow.cpp
inside the constructor:

QImage defImg=QImage(1920,1200,QImage::Format_Grayscale8);
QPixmap defStream_pix=QPixmap::fromImage(defImg);
ui->graphicsView->setScene(new QGraphicsScene(ui->graphicsView));
Item=ui->graphicsView->scene()->addPixmap(defStream_pix);

inside the constructor, a pixmap is created and added to the scene. "Item" is the returned pointer.
now I have updated the "Item" whenever there is new image and update the scene.

void MainWindow::whenNewFrame(const QImage& im)
{
    QPixmap stream_pix=QPixmap::fromImage(im);

    if (!stream_pix.isNull())
    {
        Item->setPixmap(stream_pix);
        ui->graphicsView->scene()->update();
    }
}

Thank you @Christian-Ehrlicher

/edit by moderator: added <code> tags

[Christian Ehrlicher]

Nice, then you can mark the topic as solved now :)