mode value

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Hej Witek, thanks for your answer, but I think that the maxVal and Mode Value are not the same. When I use your approach, I will get the highest bin-value but not the amount of pixels for this bin

If mode value is the most often appearing one, then the max value of the histogram if the mode value. The highest bin value will have the number of pixels of particular brightness (assuming you make your bins 1 pixel wide) that appear most often in the image. I think this is exactly what you are looking for.