now my question is that which 'a' i should take?

I is 20*20 image of class uint8;

a=im2double(I) and a=double(I) gives different result.

now generate noisy image using noisy=a+n;

where,n=0+10*randn(size(I))

now my question is that which 'a' i should take?(either a=im2double(I) ora=double(I))

Answer 1

[Image Analyst]

im2double() scales images to the 0-1 range whereas double() leaves their values alone. It just depends on what range you want the image to be in before you add noise to it.

[vipul utsav]

which is better for noise estimation as your thought?(when i want to add noise in original image manually )

[Image Analyst]

Either one can do it. I tend to not use im2double.