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what is the role of mask passed to calcHist argument ?

asked 2017-01-02 04:11:30 -0500

simozz gravatar image

updated 2017-01-02 04:11:49 -0500

I have a doubt regarding the calcHist function:

From here I read:

"Optional mask. If the matrix is not empty, it must be an 8-bit array of the same size as images[i] . The non-zero mask elements mark the array elements counted in the histogram."

Is not clear to me how can be used the mask.

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answered 2017-01-02 06:02:15 -0500

It means that all the pixels having a value, will be added with their pixel value to the histogram you create. All the others will get ignored. Exactly like stated. For example if you have a squared image of 45x45 pixels, and a mask of 45x45 pixels with a white circle of 20 pixels diameter starting from the center point, then only the pixels inside the circle will be used for calculating your histogram.

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Asked: 2017-01-02 04:11:30 -0500

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Last updated: Jan 02 '17