Remove Noise from Image

I have this RGB image.

I cropped the image into 4 equal size and then When I convert these images to binary images using im2bw. I get noisy image.

I have applied different filters but none of them worked. Can anyone suggest which filter or pre-processing technique should I use?

Answer 1

[Image Analyst]

Try using a tophat or bottomhat filter, imtophat() or imbothat(). Or else use adapthisteq().

[Li Sun]

to add to what he has said, try to convert your RGB to LAB format, then do it on the L layer, then convert back to RGB. BTW, were you able to get good result without cropping the image?