[Interest] Problem with cv::Mat grayscale to QImage

[René Hansen]

You might need to set the bytesPerLine of the QImage to match the step of
cv::Mat. I seem to recall having a similar issue once, converting between a
four and three bytes per pixel formats, e.g. if the cv::Mat is in CV_8UC4.


/René

On Thu, 20 Jun 2019 at 23:05, Jason H <jhihn at gmx.com> wrote:

> Simple code:
>
> cv::Mat left_image = cv::imread(filename, cv::IMREAD_COLOR );
> cv::cvtColor(mat, mat, cv::COLOR_BGR2GRAY);
> cv::imwrite("dummy_gray_cv.png", left_image); // ok
> QImage test((unsigned char*) left_image.data, left_image.cols,
> left_image.rows, QImage::Format_Grayscale8);
> test.save("dummy_gray_qt.png"); // skewed
>
>
> However the dummy_gray_qt.png image is not aligned correctly, it's skewed
> as if bytes are missing/being skipped.
>
> I have to convert it back to color to work:
> cv::Mat dst;
> cv::cvtColor(left_image, dst, cv::COLOR_GRAY2BGRA);
> QImage result = QImage((unsigned char*) dst.data, dst.cols, dst.rows,
> QImage::Format_RGB32);
> result.save("dummy_color_qt.png")
>
> Is there a way I can avoid needing cv::cvtColor(left_image, dst,
> cv::COLOR_GRAY2BGRA)?
>
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> https://lists.qt-project.org/listinfo/interest
>


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