# How to find brightness of given area

There are (combinations of) OpenCV functions/methods to find the difference between two frames of a video. After finding such areas I would then like to know the rate of change of brightness for those locations (between different frames). But I have yet to find an OpenCV function/method that given an area would return a value in proportion to the (average) brightness of that area. Did I miss something? Is there a set of OpenCV calls that might do this?

-thanks

Will

`meanStdDev`

solve your problem?Like @unxnut says, you basically want to see how the intensity values of your image change over time. I would look indeed at some statistical approaches like mean and standard deviation.

OK, but I only want to look at a specific area in a frame of say 100dots.

And you can easily do that by specifying that area. For example, for your

`frame`

, you can do the operation on`frame.operator()(rect)`

where`rect`

is a rectangle defining your region of interest.