Find black pixel co-ordinates in image

Hello all,

This a second part or extension of this question http://www.mathworks.com/matlabcentral/answers/126167-divide-an-image-into-n-sectors and according to this http://www.mathworks.com/matlabcentral/answers/126167#comment_208638 as answered by Jos we get the number of black pixels in each sector.

I need to find out the coordinates of black pixels in each sector, that is for every sector of 4 degree if there are any black pixels present then how to get the co-ordinates of those pixels for every sector.

Here's the sample image:-

http://i.imgur.com/cgOL1yu.png

I tried something like this to get the pixels but it ain't working : -

for i = 1 : max(SectorIdx)
     [cx1, cx2] = find(bw(SectorIdx == i) == 0)
end

But it isn't working. For the code reference see the previous post link given above.

Thank you. Any help or reference would be of great help.