Issues with opencv and image

[quixotic120]

trying to convert local webcam stream from cv::Mat to QImage but the output is weird. I've tried a bunch of things and searched for hours; I'm officially stuck.

here is the code snippet in question

void AppName::SlotFrameReady(cv::Mat image, qint64 captureTime, qint64 processTime)
{
  //  cv::Mat imageholder;
 //  cv::cvtColor(image, imageholder, CV_BGRA2RGBA);

 //   QImage img((const unsigned char*)(image.data), image.cols, image.rows, QImage::Format_Grayscale8);
 //    QImage img((const unsigned char*)(imageholder.data), imageholder.cols, imageholder.rows, QImage::Format_RGB32);
 QImage img((const unsigned char*)(image.data), image.cols, image.rows, image.step, QImage::Format_RGB888);

m_VideoView->Update(&img);

}

This is what I've tried - adding image.step, tried every QImage format, tried img.invertPixels() and img.invertRGB/invertRGBA()

I have also tried this, found on stackexchange:

void AppName::SlotFrameReady(const cv::Mat4b &image, qint64 captureTime, qint64 processTime)
{

QImage dest(image.cols, image.rows, QImage::Format_RGBA8888);
for (int y = 0; y < image.rows; ++y) {
        const cv::Vec4b *srcrow = image[y];
        QRgb *destrow = (QRgb*)dest.scanLine(y);
        for (int x = 0; x < image.cols; ++x) {
                destrow[x] = qRgba(srcrow[x][2], srcrow[x][1], srcrow[x][0], 255);
        }
     }

m_VideoView->Update(&dest);

but it results in the same broken output.

I've also tried creating a temporary image to run cvtColor and convert (tried CV_BGRA2RGB and BGRA2RGBA) and this gives the same result.

type() output is 24 which, if I am correct, is CV_8UC4 (aka 4 channels of unsigned char).

If I use any sort of above I get the following (although some formats will show incorrect color instead of just grayscale. This is with RGB8888): http://i.imgur.com/79k3q8U.png

if I output in grayscale everything works as it should: removed link bc rep isn't enough

The one thing I haven't tried is writing the mat to a file and reading it into a qimage. My thinking is that this is very inelegant and will be too slow for my needs.

another thing to note - the video view update function transforms the qimage into a qpixmap for display. could this be where the error is?

the relevant section of VideoView where it is converted to PixMap and pushed to display:

QPixmap bitmap = QPixmap::fromImage(*image).transformed(transform, Qt::SmoothTransformation);
setPixmap(bitmap); 

using the FaceTime camera built into my macbook pro as well as with 2 other USB cams I've tried (logitech c270 and a no-name garbage cam)

On mac 10.11 with QT creator 5 and opencv 2, have also tried opencv3.1 with no change. Have assumed it's an issue with opencv and I asked on their forums awhile back. While I did receive a lot of very helpful responses was not able to find a solution.

Thanks!

[SGaist]

Hi and welcome to devnet,

What image format should you be getting from OpenCV ? Are you sure you are getting BGRA ?

[quixotic120]

@SGaist Hello,
I believe opencv works in BGR. Image type is reported as CV_8UC4 which (if I'm correct) translates to an unsigned 8 bit 4 channel image which is why I've been trying BGRA - trying to convert to a 3 channel (e.g. BGR) usually crashes at runtime

thanks!

[SGaist]

The OpenCV conversion crashes ?