Image Shuffling with another image

Question

This is in continuation to a question Image Shuffling in one of my threads %# scramble autumn.tif with itself

img1 = imread('autumn.tif'); 

%# scramble 
[dummy,scrambleIdx] = sort(img1(:)); 
img2 = img1; 
img2(:) = img1(scrambleIdx); %# note the (:). If you don't use it, img2 becomes a vector 

%# unscramble 
[dummy2,unscrambleIdx] = sort(scrambleIdx); 
img3 = img2; 
img3(:) = img2(unscrambleIdx); 

Question 1:-The sort(X,dim) function arranges the columns of X in ascending order. Over here : implies all the dimensions of X? Question 2: In this code the columns and rows of img2 are shuffled or only the columns are shuffled? Plz clarify

Answer 1

1. sort(X,dim) sorts along dimension dim, i.e. sort(X,1) sorts the rows within each column, and sort(X,2) sorts the columns within each row. sortrows(X,4) sorts the rows according to the fourth row, and if you want to sort the columns, you have to transpose X first. sort(X(:) sorts all the elements of the array X.
2. In this code, all the elements of img2 are shuffled.

Instead of using autumn.tif, you may want to try shuffling on e.g. magic(5), a 5x5 magic square, so that you can better see what is going on.

EDIT

Here are the examples with magic(5)

>> m = magic(5)
m =
    17    24     1     8    15
    23     5     7    14    16
     4     6    13    20    22
    10    12    19    21     3
    11    18    25     2     9

>> sort(m,1) %# sort rows in each column of m
ans =
     4     5     1     2     3
    10     6     7     8     9
    11    12    13    14    15
    17    18    19    20    16
    23    24    25    21    22

>> sort(m,2) %# sort columns in each row of m
ans =
     1     8    15    17    24
     5     7    14    16    23
     4     6    13    20    22
     3    10    12    19    21
     2     9    11    18    25

>> sortrows(m,3) %# sort the rows of m according to column 3
ans =
    17    24     1     8    15
    23     5     7    14    16
     4     6    13    20    22
    10    12    19    21     3
    11    18    25     2     9

>> mt = m' %'# transpose m
mt =
    17    23     4    10    11
    24     5     6    12    18
     1     7    13    19    25
     8    14    20    21     2
    15    16    22     3     9

>> sortrows(mt,2) %# sort the rows of the transpose of m according to col 2
ans =
    24     5     6    12    18
     1     7    13    19    25
     8    14    20    21     2
    15    16    22     3     9
    17    23     4    10    11

>> mm = m; %# assign an output array for the next operation
>> mm(:) = sort(m(:)) %# sort all elements of m
mm =
     1     6    11    16    21
     2     7    12    17    22
     3     8    13    18    23
     4     9    14    19    24
     5    10    15    20    25