Algorithm 1: VIFM

Input: image, Target detection results, Square size m Output: m*m feature map matrix high ← image.shape0 width ← image.shape1 matrix ← $0^{m\times m}$ for (cls, x, y, w, h) ∈ results do:   center_x ← x +$\frac{w}{2}$   center_y ← y +$\frac{h}{2}$   index_width ← int($\frac{center\_x}{width}$m)   index_high ← int($\frac{center\_y}{high}$m)   if cls ≠’bus’ and cls ≠’car’ and cls ≠’trunck’     continue   end if if index_width ≥ m or index_high ≥ m or index_width < 0 or index_high < 0    continue   end if   matrix[index_width,index_high] ← matrix[index_width,index_high] + 1   end for return matrix