Abstract: Aiming at the problem that the step size of traditional multithreshold color image segmentation method was less than the fixed value of distance parameter, sometimes the step size was too large to exceed the optimal result, we proposed global segmentation method for multithreshold color images under adaptive step size. Firstly, the color image was preprocessed to solve the problem of reducing the total number of colors without reducing the quality of the color image in order to improve 
the segmentation efficiency. Secondly, according to the objective function of multithreshold color image segmentation, the chaotic optimization theory was combined with particle swarm optimization algorithm, the global segmentation objective function of multithreshold color image was solved by chaotic particle swarm optimization algorithm. Finally, combined with the  global segmentation method for multithreshold color image under adaptive step size, the optimal color image thr
eshold segmentation results were obtained. The experimental results show that the segmentation effect, accuracy, stability and convergence of this method are good.

Key words: adaptive step size, multithreshold, color image, global, segmentation