executions is fine for the first run but it is showing an error

function ImagesExample(uname1) %# read images in a cell array disp(uname1); imgs = cell(6,1); for i=1:6 imgs{i} = imread( sprintf('C:/Users/maruthi1/Documents/MATLAB/images3/ma3%1d.jpg',i) ); end

      %# show them in subplots
      figure('Name','Image_mag','Numbertitle','off');
      title('Image_mag');
      for i=1:6
          subplot(2,3,i);
          h = imshow(imgs{i}, 'InitialMag',200, 'Border','tight');
          title(num2str(i))
          set(h, 'ButtonDownFcn',{@callback,i})
      end

function callback(o,e,idx)
        %# show selected image in a new figure
        figure(2), imshow(imgs{idx})
                         title(num2str(idx))
             promptMessage = sprintf('Drag out a box that you want to copy,\nor Cancel to abort processing?');
titleBarCaption = 'Continue?';
button = questdlg(promptMessage, titleBarCaption, 'Continue', 'Cancel', 'Continue');
if strcmpi(button, 'Cancel')
  return;
end
A=imgs{idx};
n = input('Please enter the number of scenes you wish to crop: ')
ii=1;
%load user.mat
while (ii<=n)
im_cropped{ii} = imcrop(imgs{idx});
ii=ii+1;
end
for ii=1:n

     figure (4) ;
      h=[];
      h(ii)=subplot(3,4,ii);
      imshow(im_cropped{ii},'Parent',h(ii));
       percent_match(uname1,im_cropped{ii});
      ii=ii+1;
  end
   promptMessage = sprintf('Your cropped images saved successfully');
  titleBarCaption = 'Continue?';
  button = questdlg(promptMessage, titleBarCaption, 'Continue', 'Cancel', 'Continue');
  if strcmpi(button, 'Cancel')
    return;
  end
  end
  end

percent_match.m

function percent_match(uname1,imgs)
disp(uname1);
 myDir = 'user_images/';
myDir=strcat(myDir,uname1)
myDir=strcat(myDir,'/');
jpgFiles = dir([myDir '*.jpg']);
numFiles = length(jpgFiles);
mydata = cell(1,numFiles);
% mydata = zeros(numFiles);
for k = 1:numFiles
    mydata{k} = imread([myDir jpgFiles(k).name]);
    mydata{k}=rgb2gray(mydata{k});
    imgs=rgb2gray(imgs);
   mydataPoints=detectSURFFeatures(mydata{k});
   strong1 = mydataPoints.selectStrongest(50);
   imgsPoints=detectSURFFeatures(imgs);
   strong2 = imgsPoints.selectStrongest(50);
   [mydataFeatures,mydataPoints1]=extractFeatures(mydata{k},strong1);
[imgsFeatures,imgsPoints]=extractFeatures(imgs,strong2);
mydataPairs=matchFeatures(mydataFeatures,imgsFeatures);
matchedmydataPoints = mydataPoints(mydataPairs(:, 1), :);
matchedimgsPoints = imgsPoints(mydataPairs(:, 2), :);
[tform, inlierBoxPoints, inlierScenePoints] = ...
    estimateGeometricTransform(matchedmydataPoints, matchedimgsPoints, 'affine');
    boxPolygon = [1, 1;...                           % top-left
        size(mydata{k}, 2), 1;...                 % top-right
        size(mydata{k}, 2), size(mydata{k}, 1);... % bottom-right
        1, size(mydata{k}, 1);...                 % bottom-left
        1, 1];     
        newBoxPolygon = transformPointsForward(tform, boxPolygon);
        %figure;
%imshow(imgs);
%hold on;
%line(newBoxPolygon(:, 1), newBoxPolygon(:, 2), 'Color', 'y');
%title('Detected Box');
 numPairs = length(mydataPairs); %the number of pairs

    percentage  = (numPairs*2);
   if percentage < 75
       disp('we have this');
       disp(percentage);
   else
       disp('we dont have this')
   end
        end
     end

Please help me for my project.

[Walter Roberson]

I recommend that you recode using fullfile() instead of building the file names the way you do now

Answer 1

[Guillaume]

Well, clearly from the error message, you're passing a 2D matrix to rgb2gray. If you pass a 2D matrix to rgb2gray it must be a colour map which is always a matrix with 3 columns. I suspect that instead you're giving it a greyscale image. rgb2gray only works on colour images or colour maps, not greyscale images.

It's impossible for us to tell you which image is causing problem since we don't have access to them. I would suggest you learn to use the debugger. At the comment prompt, issue

dbstop if error

run your code and when it breaks into the debugger, see which rogue image (uname or imgs) is causing the issue.

You could also wrap the call to rgb2gray in a check:

switch ndims(inputimage)
   case 2  %image is already greyscale
     greyimage = inputimage;
   case 3   %colour image
     greyimage = rgb2gray(inputimage);
   otherwise
     error('not an image');
end