Question

I am new to MatLab. I am trying to do some work on image processing. I want to find element’s indexes in a matrix. If this is my matrix:

A =

92    99     1     8    15    67    74    51    58    40
98    80     7    14    16    73    55    57    64    41
 4    81    88    20    22    54    56    63    70    47
85    87    19    21     3    60    62    69    71    28
86    93    25     2     9    61    68    75    52    34
17    24    76    83    90    42    49    26    33    65
23     5    82    89    91    48    30    32    39    66
79     6    13    95    97    29    31    38    45    72
10    12    94    96    78    35    37    44    46    53
11    18   100    77    84    36    43    50    27    59

Then I want to find the indexes of elements which are greater than 50. I know one way to do it is by loops but that is very expensive if I do it on 512 X 512 or greater images.

Is there any other way? Actually I want to find it because I have an image in which there is a plain background and there is a person in it. So I want to find the points where there is a change in that plain background. Any help would be appreciated.

Answer 1

You can use find for your task

[r c] = find( A > 50 ); % now you have the row. column indices of all elements greater than 50