4f system has the characters of noise and low-pass
to remove the noise and protect the image texture of its output images
a method is proposed. Different with the classic hard threshold denoise method in NSCT domain
it adopts a smaller threshold to remove the small amplitude noise to protect the image detail better and protrude the remanent big amplitude noise
then uses the continuity of image texture to remove the large amplitude isolated noise from the consecutive image detail in the high-frequency sub-band images. Eventually the noise is removed and the image detail is protected in the same time. Experiments show that the method can reach the same degree with classic methods in denoising
and is better than classic method in protecting image detail in view of vision and numerical judgment standard. It is more suitable for the situation as the 4f system which needs protect the image detail extraordinarily.