How can I get the fringe visibility of a difference Image

To measure the fringe visibility I need to know the maximal and minamale intensities of the Image and my problem is that I cannot calculte the intensities they are always Imax = 1 and Imin = 0.

Have any anyone an Idea ? thank u for help.

Here is my Matlab code :

A=im2double(rgb2gray(imread('Diffbild_sw.tif')));

maxA=max(max(A))

minA=min(min(A))

V = (maxA-minA)/(maxA+minA);

Answer 1

[Image Analyst]

If you want the original values, don't call im2double():

rgbImage = imread('Diffbild_sw.tif');
grayImage = rgb2gray(rgbImage);
maxGrayLevel = max(grayImage(:))
minGrayLevel = min(grayImage(:))

[Khaled Jbir]

Thank u for your fast answer but i have always 1 and 0 as maxGrayLevel and minGrayLevel so the fringe visibility "V" is always = 1 it is normal ? i don´t think so so do you know maybe where is my fault ?

[Image Analyst]

Please attach the image. It sounds like a binary (black and white) image - just two gray levels.

[Khaled Jbir]

here the attached image

[Image Analyst]

Using the code I first gave up above, this is what I get:

maxGrayLevel =
  240
minGrayLevel =
    0

So there is something you're not telling us.

[Khaled Jbir]

Yes, but can I use a filter or another method so that I can avoid that the minGrayLevel=0 because if it is the case my fringe visibility will be always equal 1.

 (V = (maxGrayLevel-minGrayLevel)/(maxGrayLevel+minGrayLevel))

and it is not logic.

[Image Analyst]

The min gray level is what it is. If you don't like it being that, you can always change it. What would you change it to? That formula will always be 1 if minGrayLevel = 0 of course. But I don't think you want to just arbitrarily change your min gray level to 42 or whatever. Besides, what would you do with the other gray levels? Like gray levels 1-41 or whatever? Or the brighter gray levels? Basically if you want to fudge your data, you can make the V be whatever you want -- just plug in the desired V, the actual max gray level, and solve for the min gray level.