getting absurd result in For loop

multi = dir('D:\testing\abrupt\*.jpg');
for i = 1:2:length(multi)
    filename = strcat('D:\testing\abrupt\',num2str(i),'.jpg');
I = imread(filename);
 I1 = rgb2gray(I);
    mat1(:,:,i)= I1;
end

In the folder "multi" images are saved as 1.jpg 3.jpg 5.jpg...etc.the total number of images in "multi"was 133 and it is like 1,3,5,7....265, means only odd number of images are saved. when this code was run, the I am getting m-by-n-by-133 mat1(:,:,i) values but problem encountered is that mat1(:,:,2), mat1(:,:,4), mat1(:,:,6) or mat1(:,:,even no.) are having all matrix elements as zero whereas mat1(:,:,odd number) are giving correct result? How can I solve this problem??

Answer 1

[Jan]

The results is not absurd, but exactly as expected. Try this:

a = [];
a(1) = 1;
a(3) = 3;
disp(a)

The element a(2) is filled by a 0 implicitly. There are no "gaps" in numerical arrays. Solution:

FileList = dir('D:\testing\abrupt\*.jpg');
for iFile = 1:length(FileList)
    filename = fullfile('D:\testing\abrupt\', FileList(iFile));
    I = imread(filename);
    I1 = rgb2gray(I);
    mat1(:, :, iFile)= I1;
end

If you want to exclude the files with the even indices:

FileList = dir('D:\testing\abrupt\*.jpg');
index    = 0;
for iFile = 1:2:length(FileList)
  filename = fullfile('D:\testing\abrupt\', sprintf('%d.jpg', iFile));
  I        = imread(filename);
  I1       = rgb2gray(I);
  index    = index + 1;
  mat1(:,:, index) = I1;
end

[NAVNEET NAYAN]

Thanks Simon, It's working now...

Answer 2

[KSSV]

In the for loop you are taking only even numbers....change it to 1:1:length(multi)

multi = dir('D:\testing\abrupt\*.jpg');
for i = 1:1:length(multi)
    filename = strcat('D:\testing\abrupt\',num2str(i),'.jpg');
I = imread(filename);
 I1 = rgb2gray(I);
    mat1(:,:,i)= I1;
end

[NAVNEET NAYAN]

when i am doing for i = 1:1:length(multi) i am getting an error : File "D:\testing\abrupt\2.jpg" does not exist. Error in program_number_2(line 7) I2 = imread(filename);