Question

With the following code i detect all squares in a gray scale image:

for (;contours != null; contours = contours.HNext)
{
    var approxContour = contours.ApproxPoly(contours.Perimeter * 0.05,
       contours.Storage);

    var rect = approxContour.GetMinAreaRect();

    if (IsSquare(rect, rect.size.Height * 0.1f))
      boxes.Add(rect);
}

I’m looking for a way to filter the squares based by their color. E.g. I want to remove all squares with an average gray value less then 128.

Which OpenCv function do I have to use?

Answer 1

You have to use ROIs and GetAverage():

var rect = approxContour.GetMinAreaRect();
gray.ROI = approxContour.BoundingRectangle;
var average = gray.GetAverage();
gray.ROI = Rectangle.Empty;

if (average.Intensity > 100)
{
    continue;
}