How to calculate the average gradient of an image?

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Munshida P
Munshida P 2019-8-27
评论： Munshida P 2019-9-13
i have tried this code.But the results are mismatching.
[Gmag, Gdir] = imgradient(X, 'sobel');
AG=abs((sum(sum(mode(Gmag))/(sqrt(2)))))
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Munshida P
Munshida P 2019-8-30
Sir, i can't attach my dicom image here because,the file format is not supported.(.dcm)

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回答（3 个）

Guillaume
Guillaume 2019-8-30
Missing from your equation, is the exact definition of G. You're currently using the sobel operator to compute the gradient and as documented in the algorithms section of imgradient whichever operator you use is going to give you vastly different results for the magnitude.
I suspect that your equation use a completely different definition than 'sobel' for G.
As asked by Raunak, for us to be able to tell you what is wrong, we need the actual source image and whatever you compare it to.
Bruno Luong
Bruno Luong 2019-8-30
AG=abs((sum(sum(mode(Gmag))/(sqrt(2)))))
I can't see the denominator factor (H-1)*(W-1). And Why you use MODE?
Those two errors explain discrepency already.
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Guillaume
Guillaume 2019-8-30
So far, the issue does not appear to be matlab but maths.

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Raunak Gupta
Raunak Gupta 2019-8-30
Hi,
As per the formula you have mentioned above, the syntax for Calculating ‘AG’ is mistaken. For implementing the formula, you can use below commands.
%Here X is the array for which Gradient is to be calculated
[Gmag,Gdir] = imgradient(X,'sobel');
% Here since Gmag represent Magnitude of Gradient so no need to take absolute value
AG = sum(sum(Gmag))./(sqrt(2)*(size(X,1)-1)*(size(X,2)-1));
If you want to try other method for calculating gradient you may investigate ’method’ parameter in imgradient. Please keep in mind that imgradient works only for grayscale images and would not provide required results for RGB images. Here is the link to the documentation of imgradient.
https://www.mathworks.com/help/images/ref/imgradient.html
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PPO POT
PPO POT 2019-9-13
编辑：PPO POT 2019-9-13
https://www.sciencedirect.com/science/article/pii/S1746809418302714
This is my code, with this code you can browse image file and then calculate AG automatically,
[filename1,pathname] = uigetfile('*.*',' Select the Original Image ');
orgIM = imread(filename1);
% Pattern
%[Gmag, Gdir] = imgradient(I,'prewitt');
% 1] If test image is true color covert its to grayscale
if size(orgIM,3) == 3
testIM = rgb2gray(imread(filename1));
[Gmag,Gdir] = imgradient(testIM,'prewitt');
% Calcualte Average gradient
AG = sum(sum(Gmag))./(sqrt(2)*(size(testIM,1)-1)*(size(testIM,2)-1))
end
Munshida P
Munshida P 2019-9-13
info = dicominfo('MR-MONO2-12-an2');
X= dicomread(info);
imshow(X,[])
[Gmag,Gdir] = imgradient(X,'prewitt');
%Average gradient
AG = sum(sum(Gmag))./(sqrt(2)*(size(X,1)-1)*(size(X,2)-1 ))
got it....thank you sir

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