Divide by zero error in SEEDS Superpixels

[scloke]

• OpenCV => 4.2
• Operating System / Platform => Windows 64 Bit
• Compiler =>Visual Studio 2019

Detailed description

For opencv_contrib/modules/ximgproc/src/seeds.cpp
lines 136-141

//compute initial label for sublevels: level <= seeds_top_level
//this is an equally sized grid with size nr_h[level]*nr_w[level]
int computeLabel(int level, int x, int y) {
    return std::min(y / (height / nr_wh[2 * level + 1]), nr_wh[2 * level + 1] - 1) * nr_wh[2 * level]
            + std::min((x / (width / nr_wh[2 * level])), nr_wh[2 * level] - 1);
}

When processing a large number of images, a program crash can occur with a divide by zero error in the above function. This can be rectified by changing to the following:

//compute initial label for sublevels: level <= seeds_top_level
//this is an equally sized grid with size nr_h[level]*nr_w[level]
int computeLabel(int level, int x, int y) {
    return std::min(y * nr_wh[2 * level + 1] / height), nr_wh[2 * level + 1] - 1) * nr_wh[2 * level]
            + std::min((x * nr_wh[2 * level] / width)), nr_wh[2 * level] - 1);
}

[alalek]

Feel free to prepare PR with proposed fix (onto 3.4 branch if applicable)