Eliminate background noise of image without blurring it in matlab

The project is for 1 day only! The pictures store in: [login to view URL] I have 15 pictures that you can see "rings" in them. The rings are the main important parameter in the picture. However you can see "noise" in the background all over the picture (like squres) which i want to eliminate Need short code (4-5 lines) in matlab that: . Eliminate the backgtound noise from the picture. 2. You need to do it without bluriing the rings (especially the smallest ring in the middle of the picture)- i need to see the same ammount of rings after you filter them. 3. It should be very short code- not complicated, 4-5 lines code is best 4. Make the contrast- i mean more black and wihte without destroy info. I try to use gaussian filter with sigma=1.6, but it blurr some of the pictures (especially a3 and b1). You can see picture b1 to see the problem: In Picture 5 (b1) i draw line on part of the 3rd ring. In the gauss filter this is the last ring i can see, but in the real picture, i can see 5 rings. So i need filter that will not do it