how to sparse represent a image?

hi,

 i'm trying to create a sparse matrix for an image.
i've given the command as,

a=imread('imagename.format')

b=sparse(a)

i'm getting the output for the first command and for the second command i'm getting a error as mentioned below,

Undefined function 'sparse' for input arguments of type 'uint8'

please help thanks in advance

Answer 1

[Shoaibur Rahman]

Convert a to double first, and the use that in sparse. Make sure that a is not in 3D, if so, then make it 2D before using in sparse.

a = double(a);
b = sparse(a); % for 3D a, you may use b = sparse(a(:,:,1)); or 2 or 3 instead of 1 here.
spy(b) % see the sparsity pattern

[lohith]

thank you very much :)

[Isra Anwar]

This code is not working on pgm (greymap images) what should I be changing in this code to get a sparse representation of a grey image?

[Guillaume]

@Isra, I suggest you start your own question posting the exact code you're using and explaining what 'not working' means exactly (you get an error? if so, which? no error but not the output you want? if so what output do you want? etc.)

[Snigdha KN]

This code shows an error when executed. It shows undefined function 'sparse' for argument type 'double'