Help with Image SNR

Can anyone suggest a good way to be able to

1: estimate the average signal of the bright spots 2: Estimage the DC background level 3: The std of the background

This is my typical image

I enclose the ascii data as unable to upload tiffs

[Jason]

1: I first of all try to get the background:

im_back=imopen(im,strel('disk',40));  %Get features with radius>40 (i.e.. background)
bk=mean(im_back(:));
%se=strel('disk',2);
%z4=imerode(z3,se);

z1=im-im_back;        %Subtract Background
imshow(im_back);

2: I then do a median filter to remove any single pixels:

%Median Filter this background subtracted image
z2=medfilt2(z1,[2,2]);   
z2( z2 < 0) = 0;        %put any negative values to zero

3:Create Binary Image

%threshold on median processed, background subtracted image to create
%binary image, then fill holes
IM=z2;
%level1 = graythresh(double(z2))
mx=double(max(IM(:)))
me=mean(IM(:));
sd=std2(IM(:));
level=round(me+0.5*sd)

IM( IM < level) = 0;
IM( IM > level-1) = 1;

z3 = imfill(IM,'holes');

Im not sure Im going about this int he right way???