Constructing QImage from unsigned char* data

Question

I encountered a problem with passing Image object (captured with Point Grej FlyCapture2 SDK) to QImage object. I am getting a pointer associated with Image data by function:

virtual unsigned char* FlyCapture2::GetData  (   ) 

and then loading the data by:

QImage::QImage ( uchar * data, int width, int height, int bytesPerLine, Format format )

Formats of data of both Image objects are 8-bit monocolor. BytesPerLine parameter should be equal to width of the Image (I've already checked it by saving FlyCapture2::Image to .bmp and then loading it to QImage).

Do you thing the problem is casting from unsigned char* to uchar*? Do you have any other ideas? Copying image pixel by pixel is much too slow.

EDIT: I am converting Image captured by FlyCapture into the FlyCapture2::PIXEL_FORMAT_RGB8 , for which: R = G = B = 8 bits, within PGR::SnapShot() function. SnapShot() returns unsigned char* const. and here is a part of my Qt display function:

unsigned char *const img = PGRSystem->SnapShot();
QImage Img(img, 1024, 768, QImage::Format_RGB888);
QGraphicsScene *Scene = new QGraphicsScene();
Scene->addPixmap(QPixmap::fromImage(Img));
ui.ImageView->setScene(Scene);
ui.ImageView->fitInView(ui.ImageView->itemAt(100,100));
delete [] Scene;

I also tried to save Img to file, but got unhandled exception then. I tried other pixel format pairs (FlyCapture2::PIXEL_FORMAT_RGB - 24 bit RGB with QImage::RGB888 and FlyCapture2::PIXEL_FORMAT_RGBU32 with QImage::RGB32)

It is also worth to mention that QImage constuctor, which I am using, does not set the colorTable (I am getting exception when checking if QImage is in grayScale). I need a little more help I guess.

Answer 1

First thing - QImage doesn't support a native greyscale image, which is what it sounds as if you're getting as output - so I would be curious what Format argument you're using. Probably the easiest solution, though memory-inefficent, will be to expand your greyscale image to RGB by copying each value three times (into a new QByteArray).

An additional concern is that the particular QImage constructor you're using, does not copy the underlying data, so you need be sure the pointer returned from GetData() outlives the QImage - or force the QImage to make a copy internally, using, say, QImage::copy.

Seeing more code would help, as other respondents noted above.

Answer 2

Thanks a lot for your help, you were right about the Image formats. Unfortunatelly the main problem was associated with passing the pointer between functions. In PGR::SnapShot() I was creating FlyCapture2::Image and then I was getting the pointer to data. FlyCapture2::Image was detructed when exit the function so returned pointer was BadPtr.