Function sprs::visu::nnz_image

pub fn nnz_image<N, I, Iptr>(mat: CsMatViewI<'_, N, I, Iptr>) -> Array2<u8> where
    I: SpIndex,
    Iptr: SpIndex, 

Create an array holding a black and white image representing the non-zero pattern of the sparse matrix.

Since this is aimed at display, zeros will be mapped to 0xFF white pixels while non-zeros will be mapped to 0x00 black pixels.