As the traditional algorithms for local histogram equalization is used to enhance the contrast of an image

the output brightness is always regardless of the input image.However

this is not the desirable property in many applications where preserving the original brightness is essential

so a new algorithm of local histogram equalization is proposed.Based on the algorithm of partially overlapped sub-block histogram equalization (POSHE)

we change the way of equalizing sub-block:based on the mean

each sub-block is separated recursively into a series of sub-images with different gray ranges

then the histograms are equalized over their respective gray ranges

and finally the output of the sub-block is composed with the resulting equalized sub-images.The simulation results show that

with the new algorithm

the local details on the image can be enhanced effectively

and the original brightness can also be preserved in the meantime.Besides

scalable degree of brightness preservation may be achieved by choosing the number of recursive separation.The proposed algorithm can enhance the image in a more natural manner and hence

is very useful for many commercial purposes such as consumer electronics where brightness preservation is required.