How to extract odd values and even values from a 500x500 black image ?

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Maha Almuaikel 2022-3-6

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https://ww2.mathworks.cn/matlabcentral/answers/1664864-how-to-extract-odd-values-and-even-values-from-a-500x500-black-image

编辑： DGM 2022-3-6

I want to extract the even and odd numbers from 500x500 black matrix to turn them white without using loops or conditions statement.

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Maha Almuaikel 2022-3-6

pardon me I was not clear, I mean the odd and even index from the zeros matrix

Image Analyst 2022-3-6

You're still not clear. Zero is neither an odd number or an even number.

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Answer 1

Image Analyst 2022-3-6

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https://ww2.mathworks.cn/matlabcentral/answers/1664864-how-to-extract-odd-values-and-even-values-from-a-500x500-black-image#answer_911239

编辑：Image Analyst 2022-3-6

在 MATLAB Online 中打开

Do you have any other numbers other than 0? If so you can use rem(M, 2). Observe:

M = magic(5)
M = 5×5
    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
mCopy = M;
oddIndexes = rem(mCopy, 2) == 1
oddIndexes = 5×5 logical array
   1   0   1   0   1
   1   1   1   0   0
   0   0   1   0   0
   0   0   1   1   1
   1   0   1   0   1
oddNumbers = M(oddIndexes) % Extract the odd numbers.
oddNumbers = 13×1
    17
    23
    11
     5
     1
     7
    13
    19
    25
    21
% Turn the odd numbers to white (255)
mCopy(oddIndexes) = 255
mCopy = 5×5
   255    24   255     8   255
   255   255   255    14    16
     4     6   255    20    22
    10    12   255   255   255
   255    18   255     2   255
evenIndexes = rem(mCopy, 2) == 0
evenIndexes = 5×5 logical array
   0   1   0   1   0
   0   0   0   1   1
   1   1   0   1   1
   1   1   0   0   0
   0   1   0   1   0
evenNumbers = M(evenIndexes)
evenNumbers = 12×1
     4
    10
    24
     6
    12
    18
     8
    14
    20
     2
% Turn the even numbers to white (255)
mCopy = M; % Reset mCopy so there are no 255's in there anymore.
mCopy(evenIndexes) = 255
mCopy = 5×5
    17   255     1   255    15
    23     5     7   255   255
   255   255    13   255   255
   255   255    19    21     3
    11   255    25   255     9

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Answer 2

DGM 2022-3-6

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https://ww2.mathworks.cn/matlabcentral/answers/1664864-how-to-extract-odd-values-and-even-values-from-a-500x500-black-image#answer_911339

编辑：DGM 2022-3-6

在 MATLAB Online 中打开

Consider the matrix:

A = randi([10 99],5,5)
A = 5×5
    37    23    33    22    34
    58    58    16    79    86
    11    39    73    93    97
    11    37    92    79    19
    32    19    47    48    85
% get elements from odd linear indices
oddelems = A(1:2:numel(A))
oddelems = 1×13
    37    11    32    58    37    33    73    47    79    79    34    97    85
% get elements from even linear indices
evenelems = A(2:2:numel(A))
evenelems = 1×12
    58    11    23    39    19    16    92    22    93    48    86    19

That's linear indices. Maybe you want to address odd or even rows/columns:

% get elements from odd rows
oddrows = A(1:2:size(A,1),:)
oddrows = 3×5
    37    23    33    22    34
    11    39    73    93    97
    32    19    47    48    85
% get elements from even rows
evenrows = A(2:2:size(A,1),:)
evenrows = 2×5
    58    58    16    79    86
    11    37    92    79    19

... and so on for columns

EDIT: I'm dumb. I forgot you wanted to set pixels to white.

The above still holds. You're still trying to address your array. Just apply that to an assignment:

B = zeros(5)
B = 5×5
   0     0     0     0
   0     0     0     0
   0     0     0     0
   0     0     0     0
   0     0     0     0
B(1:2:numel(B)) = 1 % set odd linear indices to 1
B = 5×5
   0     1     0     1
   1     0     1     0
   0     1     0     1
   1     0     1     0
   0     1     0     1