1. A method for detecting polyp candidates in a medical image, comprising: applying a filter to an image of a colon to generate a response image; and identifying polyp candidates in tagged stool and clean sections of the colon in the response image, wherein the image of the colon is acquired from a medical imaging device, wherein the filter is represented by the following formula: M ⁡ ( x ) ⁢ = ∫ ∀ y ⁢ ε ⁢ V ′ ⁢ S ⁡ ( m , θ , r , y ) ⁢ ⁢ Δ ⁢ ⁢ y T ⁡ ( V ′ ) , where 
 S ( m, θ, r, y )= S 1 (m)×S 3 ( y )×(S 2( θ, r, y )+ S 5 (θ , r, y ), where M(x) is an output of the filter at a location x within the image of the colon, y is another location in the image of the colon, m is a magnitude of a gradient at y, r is a radial distance from y to x, θ is an angle between the gradient at y and a ray from x to y, V′ is a volume of the image of the colon and T is a weighting based on a size of the volume, wherein the method is performed using a processor.