How to get the noise only image?

[tjucruiser]

Under the same circumstances, I get 15 X ray images I1, I2, I3, …,I15.
Then two methods were used to get the noise only image.

First method:
Noise image=(I1-I2)/sqrt(2).
They said that subvided by sqrt(2) can maintain the variance of the Noise image identical to I1 and I2.

Second method:
Noise image=I1-(I1+I2+I3+…+I15)/15. Can this method maintain the variance of noise image identical to original images?

If I don't consider the coefficient of sqrt(2), I think first method can also be explained as
Noise image=I1-(I1+I2)/2.
The above equation is similar to second method.

Please give me some suggestion, Thank you.

 

[Jan Brittenson]

Are the images identical differing only in random noise?
Or are they different with fixed noise?

 

[tjucruiser]

The images identical differing only in random noise.

 

[Lars]

since noise varies between images I'd be inclined to calc a mean from all images and then diff each image to the mean.

 

[tjucruiser]

Lars Vinberg, thank you! I think you are right. But can you give me the mathematical deduction. If I have N images with radom noise, and I have them added on, I can eliminate the radom off from the image.

 

[Lars]

You can average out noise, not eliminate.

mean = (I1 + I2 +... + I15) / 15

That's the best you can do using mean, I think.

If you want to get into denoising raster algorithms, that's a different thing.