What is the OpenCV template matching Max Min value range ? Need to be used as a theshold / c++/java

c++, image-processing, java, opencv, template-matching

Solution

`MinMaxLocResult` does not return `minVal` and `maxVal` range. `minVal` and `maxVal` are just minimum and maximum matching scores as can be seen in the link.

The structure `MinMaxLocResult` has also `minLoc` and `maxLoc` properties which are of type `Point`, giving the matching locations. Given that you use `TM_SQDIFF` or `TM_SQDIFF_NORMED` as a matching criterion , the best matching location will be `mmr.minLoc`.

In order to set a threshold for the detection, you can declare a variable`double thresholdMatch` and set its value experimentally. if minVal < thresholdMatch then it can be said that target object is detected

Problem

I am creating a simple openCV application using template matching where I need to compare find a small image in a big image and return the result as true(if match found) or false( no matches found). ``` Imgproc.matchTemplate(largeImage, smallImage, result, matchMethod); Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat()); MinMaxLocResult mmr = Core.minMaxLoc(result); double minMaxValue = 1; if (matchMethod== Imgproc.TM_SQDIFF || matchMethod== Imgproc.TM_SQDIFF_NORMED) { minMaxValue = mmr.minVal; useMinThreshold = true; } else { minMaxValue = mmr.maxVal; } ``` Now the problem is in taking decision (true/false) using this minMaxValue. I know the above two methods TM_SQDIFF and TM_SQDIFF_NORMED returns low values while the others return high values so I can have 2 different thresholds and compare one of threshold (depending on the template method type). So it would be great if some one can explain what is the minVal and maxVal range that the MinMaxLocResult returns. Is it 0 to 1 range? If yes, for Max type template method value 1 is a perfect match?

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