How can I convert the 8*8 matrix a to 4*4 matrix b using downsample

downsample for raw and column and save the result in one matrix like b

for example:

a=

   [1 2 8 5 4 7 5 9;

   4 8 3 6 7 1 2 11;

   7 8 2 1 7 7 7 9;

   11 5 7 0 9 7 6 5;

   7 8 9 6 0 0 8 7;

   9 6 7 2 6 3 2 1;

   1 1 2 4 5 8 9 6;

   0 7 8 9 6 3 5 4]

b=

   1 8 4 5

   7 2 7 7

   7 9 0 8

   1 2 5 9

Answer 1

[Azzi Abdelmalek]

A(1:2:end,1:2:end)

[Batool Engineer]

Thanks so much, but I want the matrix b by using downsample, how can I do it.

[Azzi Abdelmalek]

a=[1 2 8 5 4 7 5 9;
 4 8 3 6 7 1 2 11;
 7 8 2 1 7 7 7 9;
 11 5 7 0 9 7 6 5;
 7 8 9 6 0 0 8 7;
 9 6 7 2 6 3 2 1;
 1 1 2 4 5 8 9 6;
 0 7 8 9 6 3 5 4]
[n,m]=size(a);
a1=reshape(downsample(a,2),[],m)
out=reshape(downsample(a1',2),[],size(a1,1))'

[Batool Engineer]

thank you so much.

Answer 2

[Guillaume]

The two answers you've got are downsampling, using nearest neighbour interpolation.

More advanced ways of downsampling your matrix would be to use imresize, e.g.

imresize(a, 0.5, 'nearest')  %nearest neighbour interpolation
imresize(a, 0.5, 'bilinear') %bilinear interpolation
imresize(a, 0.5, 'bicubic')  %etc.

[Batool Engineer]

I want to write ' downsample ' instruction, e.g. b=downsample(a,2)

but in command window appear b =

     1     2     8     5     4     7     5     9
     7     8     2     1     7     7     7     9
     7     8     9     6     0     0     8     7
     1     1     2     4     5     8     9     6

but I want for columns also.