# Video/Imagstitching assertion failed in Image blending

**URL:** <https://forum.opencv.org/t/video-imagstitching-assertion-failed-in-image-blending/17174>\
**Category:** C++\
**Tags:** stitching\
**Created:** [April 5, 2024, 2:07pm UTC](https://forum.opencv.org/t/video-imagstitching-assertion-failed-in-image-blending/17174 "2024-04-05T14:07:46Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![pascalHSW](https://avatars.discourse-cdn.com/v4/letter/p/5f9b8f/32.png) [@pascalHSW](https://forum.opencv.org/u/pascalHSW)\
**Post date:** [April 5, 2024, 2:07pm UTC](https://forum.opencv.org/t/video-imagstitching-assertion-failed-in-image-blending/17174/1 "2024-04-05T14:07:46Z")

</div>

Hey guys,  
I´m currently working on an implementation to use opencv stitching lib for video stitching.  
Now I´m facing the problem that as soon as I try to feed the blender with data, an assertion fails with the following message.

> “OpenCV(4.9.0) Error: Assertion failed (y == 0 || (data && dims \>= 1 && (unsigned)y \< (unsigned)size.p[0])) in cv::Mat::ptr, file D:\Repos\opencv\modules\core\include\opencv2/core/mat.inl.hpp, line 715”

In this peace of code:

```auto
void Blender::feed(InputArray _img, InputArray _mask, Point tl)
{
    Mat img = _img.getMat();
    Mat mask = _mask.getMat();
    Mat dst = dst_.getMat(ACCESS_RW);
    Mat dst_mask = dst_mask_.getMat(ACCESS_RW);

    CV_Assert(img.type() == CV_16SC3);
    CV_Assert(mask.type() == CV_8U);
    int dx = tl.x - dst_roi_.x;
    int dy = tl.y - dst_roi_.y;

    for (int y = 0; y < img.rows; ++y)
    {
        const Point3_<short> *src_row = img.ptr<Point3_<short> >(y);
        --> Point3_<short> *dst_row = dst.ptr<Point3_<short> >(dy + y); //Here is the fail!
        const uchar *mask_row = mask.ptr<uchar>(y);
        uchar *dst_mask_row = dst_mask.ptr<uchar>(dy + y);

        for (int x = 0; x < img.cols; ++x)
        {
            if (mask_row[x])
                dst_row[dx + x] = src_row[x];
            dst_mask_row[dx + x] |= mask_row[x];
        }
    }
}

```

y = 0 and dy = -110.

It looks like the assert fails because the data field is `data=""`. But when I go back in the Callstack it looks like there is Data in cv::Mat.

Please if someone could help me.

Thanks

Best regards

Pascal