Interpolating 1 dimensional array using OpenCV

Question

I define an array of 2 values, and try to use the imgproc module's resize function to resize it to 10 elements with linear interpolation as interpolation method.

cv::Mat input = cv::Mat(1, 2, CV_32F);
input.at<float>(0, 0) = 0.f;
input.at<float>(0, 1) = 1.f;
cv::Mat output = cv::Mat(1, 11, CV_32F);
cv::resize(input, output, output.size(), 0, 0, cv::INTER_LINEAR);
for(int i=0; i<11; ++i)
{
    std::cout<< output.at<float>(0, i) << " ";
}

The output I would have expected is:

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

What I get however is:

0 0 0 0.136364 0.318182 0.5 0.681818 0.863636 1 1 1

Clearly, my understanding of how resize works is wrong at a fundamental level. Can someone please tell me what I am doing wrong? Admittedly, OpenCV is an overkill for such simple linear interpolation, but please do help me with what is wrong here.

Answer 1

It's really simple. OpenCV is an image processing library. So you should remember that we are working on images.

Take a look at the output when we have only 8 pixels in destination image

0 0 0.125 0.375 0.625 0.875 1 1

If you take a look at this image it's very straightforward to understand resize behaviour

As you can see in this link you're using a Image transformation library: "The functions in this section perform various geometrical transformations of 2D images"

You want this results

but it will not interpolate properly the original 2 pixels image