Effect that apply circle hough transformation.
Algorithm steps:
1) Convert to gray scale;
2) Apply sobel filter (edge detection);
3) Circle hough transformation, accumulating circle radius;
4) Verifiy possible circles.
Effect that apply sobel edge detection filter.
Two 3x3 convolution masks are applied to each pixel.
One with a horizontal trend and one with a vertical trend.
The result of the each convolution is treated a vector representing
the edge through the current pixel.