C++AMP Computing gradient using texture on a 16 bit image

Question

I am working with depth images retrieved from kinect which are 16 bits. I found some difficulties on making my own filters due to the index or the size of the images. I am working with Textures because allows to work with any bit size of images.

So, I am trying to compute an easy gradient to understand what is wrong or why it doesn't work as I expected.

You can see that there is something wrong when I use y dir.

For x:

For y:

That's my code:

typedef concurrency::graphics::texture<unsigned int, 2> TextureData;
typedef concurrency::graphics::texture_view<unsigned int, 2> Texture

cv::Mat image = cv::imread("Depth247.tiff", CV_LOAD_IMAGE_ANYDEPTH);

//just a copy from another image
cv::Mat image2(image.clone() );


concurrency::extent<2> imageSize(640, 480);
int bits = 16;

const unsigned int nBytes = imageSize.size() * 2; // 614400


{
    uchar* data = image.data;

    // Result data
    TextureData texDataD(imageSize, bits);
    Texture texR(texDataD);


    parallel_for_each(
        imageSize,
        [=](concurrency::index<2> idx) restrict(amp)
    {
        int x = idx[0];
        int y = idx[1];

        // 65535 is the maxium value that can take a pixel with 16 bits (2^16 - 1)
        int valX = (x / (float)imageSize[0]) * 65535;
        int valY = (y / (float)imageSize[1]) * 65535;

        texR.set(idx, valX);
    });
    //concurrency::graphics::copy(texR, image2.data, imageSize.size() *(bits / 8u));
    concurrency::graphics::copy_async(texR, image2.data, imageSize.size() *(bits) );

    cv::imshow("result", image2);
    cv::waitKey(50);
}

Any help will be very appreciated.

Answer 1

Your indexes are swapped in two places.

int x = idx[0];
int y = idx[1];

Remember that C++AMP uses row-major indices for arrays. Thus idx[0] refers to row, y axis. This is why the picture you have for "For x" looks like what I would expect for texR.set(idx, valY).

Similarly the extent of image is also using swapped values.

int valX = (x / (float)imageSize[0]) * 65535;
int valY = (y / (float)imageSize[1]) * 65535;

Here imageSize[0] refers to the number of columns (the y value) not the number of rows.

I'm not familiar with OpenCV but I'm assuming that it also uses a row major format for cv::Mat. It might invert the y axis with 0, 0 top-left not bottom-left. The Kinect data may do similar things but again, it's row major.

There may be other places in your code that have the same issue but I think if you double check how you are using index and extent you should be able to fix this.