In this first recipe, we will present some very basic low-pass filters. In the introductory section of this chapter, we learned that the objective of such filters is to reduce the amplitude of the image variations. One simple way to achieve this goal is to replace each pixel with the average value of the pixels around it. By doing this, the rapid intensity variations will be smoothed out and thus replaced by more gradual transitions.
The objective of the cv::blur function is to smooth an image by replacing each pixel with the average pixel value computed over a rectangular neighborhood. This low-pass filter is applied as follows:
cv::blur(image,result, cv::Size(5,5)); // size of the filter
This kind of filter is also called a box filter. Here, we applied it by using a 5x5 filter in order to make the filter's effect more visible. Our original image is the following:
The result of the filter being applied on the preceding image is...