Problem with noise reduction in the photograph

I am curious about whether you could or could not see noise reduction at the scale 1:1. Others have said that you could only see it at the said scale. I tested this and found that you could also see it if the image is above 74 pixels on the screen. Has anyone ever tried this and found the same thing as I did? And if you did, could you lessen the size such that even if there are different sizes, you could still see noise reduction?
