Dividing the circular mask -have read previous posts

Hi Everyone, I have read the previous posts of members using circular mask and dividing this mask into various sectors. The posts are quite helpful and I tried to implement them; by trying to implement atan2 to compute the angle and then dividing the region based on angle regions. My question is that; the succeeding masks generated by me for dividing the circle by specifying angle intervals all end up as zeros. I do get a circular mask between -pi/4 and pi/4, but on multiplying it with the image I just get a white circle. I hope to see the section of region computed by my mask but I dont I am not sure where I am going wrong. My image size is 128x128 and the radius is 64,64 (centre of the image). Angle=atan2(64,64)to compute angle and from here I specifiy four quadrant masks which lie between 0-90; 90-180; 180-270 and 270 and 360 using q1= circular mask & angle between regions. On convolution of image with each of these masks I get only black images and an image with white circle for quadrant 1. Can anyone please guide me on this. I need to implement a circular mask which splits the region obtained by multiplying the mask with image into two regions. I am planning to rotate this mask to get subsequent regions. Any help will be appreciated. Cheers. IA

[Image Analyst]

Can we see your code?