how to obtain the values of a square matrix inside a circular region of image?
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as825
el 16 de Nov. de 2013
Comentada: as825
el 22 de En. de 2014
Suppose we find a circular roi in an image. How to obtain the values of a square matrix or square area inside that circle. give that the x and y coordinates of the circle and its radius
4 comentarios
Walter Roberson
el 16 de Nov. de 2013
"Largest" in which sense? The greatest area? If so then in a circle the rectangle with the greatest area is a square.
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Walter Roberson
el 16 de Nov. de 2013
d = r/sqrt(2);
xcoords = [x-d x+d x+d x-d x-d];
ycoords = [y-d y-d y+d y+d y-d];
line(xcoords, ycoords)
Now what you need to deal with is the rounding to integer coordinates. Rounding towards the center is the safest way. I would need to think more to figure out if there are circumstances under which it might then be possible to get a slightly larger area by extending one pixel further in one direction.
4 comentarios
Walter Roberson
el 16 de Nov. de 2013
Extracting pixel values:
YourImage(x-d:x+d, y-d:y+d)
In terms of area, Yes, any maximal square inside the circle would do, up to the effects of area reduction due to round-off of non-integers. Circles have no inherent internal orientation, so a square aligned with the axis will have the same area (to within round-off) as a square at (say) 17.29 degrees relative to the origin.
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