fn filter_internal(
method: FilterType,
bpp: usize,
len: usize,
previous: &[u8],
current: &[u8],
output: &mut [u8],
) -> FilterTypefn filter_internal(
method: FilterType,
bpp: usize,
len: usize,
previous: &[u8],
current: &[u8],
output: &mut [u8],
) -> FilterType