Find the average image of a set of images

Hello,

I need to calculate the average image of a training set images but I don't have any idea how to do it.

Thank you in advance !

Answer 1

[Image Analyst]

How about just doing a for loop:

for k = 1 : numberOfImages
  thisImage = double(imread(files(k).filename)); % Or whatever...
  [rows columns numberOfColorBands] = size(thisImage);
  % First do a check for matching rows, columns, and number of color channels.  Then:
  if k == 1
    sumImage = thisImage;
  else
    sumImage = sumImage + thisImage;
  end
end
sumImage = sumImage / numberOfImages;

If you want, you can then either leave sumImage as double

imshow(sumImage, []);  % Use []

or cast back to uint8 or uint16

sumImage = uint8(sumImage);
imshow(sumImage);  % [] is optional now.
I do it all the time and it's fast

[Image Analyst]

Referring to your answer, I hadn't seen your code yet. Obviously my files(k).filename should be your jpegFiles(k).name. Plus make sure you do the size check for robustness. It's not robust unless you check for that because it's dangerous to assume that all your images will be the same size. Even if they are, it can't hurt and makes it more robust should someone decide to borrow that snippet of code for another averaging app.

Answer 2

[Kuno Meyer]

@Image Analys, you should also care about clipping. Use im2double() before accumulation and im2uint8() afterwards.

[Image Analyst]

Yes, that's true. Good catch. I'll fix it.

Answer 3

[K.]

Thanks for the answer!

I've already read and displayed the images using this code :

myFolder = 'C:\Users\***\Desktop\barcelona';
      if ~isdir(myFolder)
        errorMessage = sprintf('Error: The following folder does not 
      exist:\n%s', myFolder);
      uiwait(warndlg(errorMessage));
      return;
      end
filePattern = fullfile(myFolder, '*.jpg');
jpegFiles = dir(filePattern);
for k = 1:length(jpegFiles)
      baseFileName = jpegFiles(k).name;
      fullFileName = fullfile(myFolder, baseFileName);
      fprintf(1, 'Now reading %s\n', fullFileName);
      imageArray = imread(fullFileName);
      imshow(imageArray);  % Display image.
      drawnow; % Force display to update immediately.
end

and tried to use the loop you mentioned but I didn't understand for what "files" refer to:

for k = 1 : 48
  thisImage = imread(files(k).fullFileName); % Or whatever...
  [rows columns numberOfColorBands] = size(thisImage);
  % First do a check for matching rows, columns, and number of color channels.  Then:
  if k == 1
    sumImage = thisImage;
  else
    sumImage = sumImage + thisImage;
  end
end
sumImage = sumImage / 48;

An error appears telling me that "files" is an ndefined variable or class "files".

Thanks again.

Answer 4

[kavya k]

sir, i am trying to perform the averaging of 30 images . i am unable to clear that error can any one help me please......

Answer 5

[kavya k]

sir, i am trying to perform the averaging of 30 images . i am unable to clear that error can any one help me please...... i have attached the .m file please once check and help me out

[Image Analyst]

Lots of stuff wrong with that. See improved version below.

clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 30;

filenames{1} = '20170508115706551.bmp';
filenames{2} = '20170508115706871.bmp';
filenames{3} = '20170508115707191.bmp';
filenames{4} = '20170508115707511.bmp';
filenames{5} = '20170508115708150.bmp';
filenames{6} = '20170508115708470.bmp';
filenames{7} = '20170508115708790.bmp';
filenames{8} = '20170508115709110.bmp';
filenames{9} = '20170508115709433.bmp';
filenames{10} = '20170508115709750.bmp';
filenames{11} = '20170508115710070.bmp';
filenames{12} = '20170508115710711.bmp';
filenames{13} = '20170508115711031.bmp';
filenames{14} = '20170508115711670.bmp';
filenames{15} = '20170508115712310.bmp';
filenames{16} = '20170508115712630.bmp';
filenames{17} = '20170508115712950.bmp';
filenames{18} = '20170508115713590.bmp';
filenames{19} = '20170508115713912.bmp';
filenames{20} = '20170508115714230.bmp';
filenames{21} = '20170508115714550.bmp';
filenames{22} = '20170508115715192.bmp';
filenames{23} = '20170508115715510.bmp';
filenames{24} = '20170508115715830.bmp';
filenames{25} = '20170508115716470.bmp';
filenames{26} = '20170508115716790.bmp';
filenames{27} = '20170508115717431.bmp';
filenames{28} = '20170508115717751.bmp';
filenames{29} = '20170508115718070.bmp';
filenames{30} = '20170508115718390.bmp';
count = 0;
for k = 1 : length(filenames)
  thisFileName = filenames{k};
  if exist(thisFileName, 'file')
    thisImage = double(imread(thisFileName));
    if k == 1
      sumImage = thisImage;
    else
      sumImage = sumImage + thisImage;
    end
    count = count + 1;
  end
end
meanImage = sumImage / count;

figure
imshow(meanImage, []);
axis on;
title('Mean Image', 'FontSize', 30);

[Orhan Albayrak]

I have tried to run this code but i have encountered with an errror. It said to me that-->

Array dimensions must match for binary array op.

Error in assign2 (line 64)

sumImage = sumImage + thisImage;

so what can i do now?

[Image Analyst]

Well obviously thisImage is a different size than sumImage. What sizes are they? Look in the workspace, or use the size() function

[rows, columns, numberOfColorChannels] = size(sumImage)
[rows2, columns2, numberOfColorChannels2] = size(thisImage)
if isequal(size(sumImage), size(thisImage))
    sumImage = sumImage + thisImage;
else
    warningMessage = sprintf('Image sizes do not match.\nCheck sizes in the command window\n')
    uiwait(errordlg(warningMessage));
    return;
end

[Orhan Albayrak]

Thank you for helping me :)