# How to calculate the mean of an image?

138 views (last 30 days)
bh dhouha on 16 Feb 2015
Commented: Kweku Nkrumah on 15 Jun 2018
How to calculate the mean of an image? Does the code mean2(img) give the right result?

Image Analyst on 16 Feb 2015
To calculate the mean of all pixels in the image, without regard to what color channel they came from (if it's a color image), you do
meanIntensity = mean(img(:));
What you did will not do it, as I'm sure you found out.
bh dhouha on 16 Feb 2015
Edited: bh dhouha on 16 Feb 2015
Thank you very much :) just a little thing : i used mean(mean(img1(:,:,1)))and it gave me the same result as mean(img1(:)).The first code is focused on the red channel only i think-as you answered me in another question- so how could it be the same result?
Image Analyst on 16 Feb 2015
It could be the same if the image was gray since the blue and green channel would be identical to the red channel. It would also be the same for lots of other cases, like where the green and blue channels are scrambled (spatially rearranged) versions of the red channel since they would have the same pixel values regardless of how they're rearranged.

Rashmi.D Jeya kumar on 8 Jan 2018
meanval = mean2(I) you can get mean value of an image
##### 3 CommentsShow 1 older commentHide 1 older comment
Image Analyst on 13 Jun 2018
Why does that mean anything is wrong? Maybe you took a bunch of photos through a microscope and they all have the same mean brightness (or really close to each other). Doesn't seem inherently unusual to me. Why do you think it indicates something is wrong?
Kweku Nkrumah on 15 Jun 2018
Ok. I get it now. Thank you.