CODEWITHSUNDEEP
c++opencv
Mohammad Asif
Mohammad Asif

Reputation: 113

convertTo not working in opencv

I am trying to use convertTo() in opencv C++. But an error pops saying

left of:convertTo must have class/struct/union

the program is below:

for (i = 0; i < height; i += 8)
{
    for (j = 0; j < width; j += 8)
    {
        Mat block = dctImage(Rect(j, i, 8, 8));
        vector<Mat> planes;
        split(block, planes);
        vector<Mat> outplanes(planes.size());
        for (k = 0; k < planes.size(); k++) {
            planes[k].convertTo(planes[k], CV_32FC1);
            dct(planes[k], outplanes[k]);
            outplanes[k].convertTo(outplanes[k], CV_8UC1);
        }
    }
}

Upvotes: 4

Views: 491

Answers (2)

Emile
Emile

Reputation: 11721

The Left:of statement suggests that its null or undefined i.e. outplanes[k] does not contain what you think it should.

I did a quick search and it looks like this could be a compiler issue whereby it has difficulty understanding/interpreting the line ...

vector<Mat> outplanes(planes.size());

https://en.wikipedia.org/wiki/Most_vexing_parse

What is outplanes? Is it being instantiated correctly?

The 'Most_vexing_parse' article suggests helping the compiler with extra parenthesis

vector<Mat> outplanes((planes.size()));

Kinda depends on your code and what the outplanes method/class is actually doing, but i imagine it's not returning what you think it should be.

Upvotes: 1

nils
nils

Reputation: 2534

I'm not sure if .convertTo() can handle the case of identical source and destination. You may want to try using a pair of temporary variables to get around your error message. Here is the relevant part from your example:

    // ...
    for (k = 0; k < planes.size(); k++) {
        Mat planes_k, outplanes_k;                     // <-- Added temporaries.
        planes[k].convertTo(planes_k, CV_32FC1);
        dct(planes_k, outplanes_k);
        outplanes_k.convertTo(outplanes[k], CV_8UC1);
    }
    // ...

UPDATE

According to the source code of .convertTo() my suggestion isn't really required (thanks pointing this out, @boaz001).

Upvotes: 1

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