  K{\"o}hler's method is a useful multi-thresholding technique based on
boundary contrast. However, the direct algorithm has a too high complexity-O(N
2) i.e. quadratic with the pixel numbers N-to process images at a sufficient
speed for practical applications. In this paper, a new algorithm to speed up
K{\"o}hler's method is introduced with a complexity in O(N M), M is the number
of grey levels. The proposed algorithm is designed for parallelisation and
vector processing , which are available in current processors, using OpenMP
(Open Multi-Processing) and SIMD instructions (Single Instruction on Multiple
Data). A fast implementation allows a gain factor of 405 in an image of 18
million pixels and a video processing in real time (gain factor of 96).
