how calculate the Background noise in an image?

how can i calculate the Background noise in an image?

Answer 1

[Image Analyst]

Take a picture of the background and compute the standard deviation of it. How about that? Or do the same to a smooth part of the image. Should work if you have additive Gaussian noise, but there are lots of different kinds of noise. Can you post an image and say what you want to do with this information?

[dziri halima]

i do not understand what i need do to calculate in practic.

[Image Analyst]

stDev = std(backgroundImage(:));

[dziri halima]

thank you sir; i used it but This result is obtained on Undefined variable backgroundImage.

Error in ==> algori at 94 stDev = std(backgroundImage(:))

[Image Analyst]

Please give the error message. ALL OF IT. I need all the red text, not just a small chunk of it like you did. Maybe backgroundImage needs to be cast as double, or maybe you are not using that same name for the variable in your image. Maybe you used "grayImage" or the hated "I" or some other name. I won't know until you post the entire error.

[dziri halima]

i work with scintigraphy image and to calculate the ejection fraction i need to calculate the background noice to remove it .

[Image Analyst]

Did you see my latest comment??? I asked you for something in it.

[dziri halima]

??? Undefined variable backgroundImage.

Error in ==> algori at 94 stDev = std(backgroundImage(:))

>> this is the all red text;

[Image Analyst]

Exactly like I suggested before: "you are not using that same name for the variable in your image." What is your background image called?

[dziri halima]

ok sir i defined bachgroundImage like this :

b = imread('image5.jpg');
b=b(:,:,1);
a=fspecial('average',[5 5]);
    G=imfilter(b,a);
  G1=imadjust(G);
    backgroundImage=double(G1);
    stDev = std(backgroundImage(:))

is it correct ?

then i obtained the result but I'm not sure if this result is correct or not. i want calculate the background noise in small region of the image how can i do it?

this is the image

[Image Analyst]

That looks right. Perhaps in the code you misspelled backgroundImage as bachgroundImage or something????

[dziri halima]

in your first comment you said that there are lots of different kinds of noise.please can you explain it and how can i know the kinds of noice in my image ? i want know if The method of calculating background noice changing with kinds of noice ?

[Image Analyst]

There's additive Gaussian noise, Poisson noise, 1/f noise, shot noise, and other kind of stochastic noise. In addition there are systematic noises like fixed pattern noise, quantization noise, etc. The Internet is a better source of education for you than I am, so I encourage you to learn more about noise. I'm not able to give you a course on noise here in the Answers forum for many reasons.

[dziri halima]

Thank you for your answers

Answer 2

[Muhammad Usman Saleem]

what kind of noise you are talking about?

[dziri halima]

 i don't know  the kind of noise in my image ,i want know it !!!!

[Muhammad Usman Saleem]

share image please?

[dziri halima]

</matlabcentral/answers/uploaded_files/34576/image1.jpg> i work with scintigraphy image

[Muhammad Usman Saleem]

i am sharing with you my two lectures , please read it your solution is here. (if you resolve the matter please accept my answer)