Hi Kenneth,
I'm not quite sure what you're doing but you seem to be picking off consecutive 3 bit sequences in the buf vector and interpreting them as integers? For example, the bit_range for p2 references bit_offset 3 into the first byte while p3 references bit 6 in the first byte. And indeed the value for v2 is 5 which is what I'd expect though v3's value is 1 rather than 4.
When reading a 3bit tiff image for instance I would have a byte array and need to pick off 3bit unsigned integers. There was a bug in gil that I have fixed. I also would like to add some test code to make sure we can detect problems earlier. But that test code needs to run on big and little endian machines.
So I'd naively I'd expect the big endian bit sequence above to yield:
101 101 100 110 110 111 011 011
resulting in values for v1 to v8 as:
5 5 4 6 6 7 3 3
Seems like bytes are read left to right on big endian machines. It's the other way around on my machine. Could you do me a favor and run again the code below. #include <cassert> #include <vector> #include <boost/assert.hpp> #include <boost/gil/gil_all.hpp> using namespace std; using namespace boost; using namespace gil; int main() { typedef bit_aligned_image1_type< 3, gray_layout_t >::type gray3_image_t; typedef gray3_image_t image_t; typedef image_t::view_t view_t; typedef view_t::reference ref_t; typedef bit_aligned_pixel_iterator< ref_t > iterator_t; std::vector< unsigned char > buf( 4 ); int x = 1; if( *( char*) &x ) { //small endian // bit pattern is: 1011 0110 0110 1101 1101 1011 // each byte is read right to left buf[0] = 182; buf[1] = 109; buf[2] = 219; } else { //little endian // bit pattern is: 1101 1011 0110 1101 1011 0110 // each byte is read right to left buf[0] = 219; buf[1] = 109; buf[2] = 182; } iterator_t it( &buf[0], 0 ); ref_t p1 = *it; it++; ref_t p2 = *it; it++; ref_t p3 = *it; it++; ref_t p4 = *it; it++; ref_t p5 = *it; it++; ref_t p6 = *it; it++; ref_t p7 = *it; it++; ref_t p8 = *it; it++; unsigned char v1 = get_color( p1, gray_color_t() ); unsigned char v2 = get_color( p2, gray_color_t() ); unsigned char v3 = get_color( p3, gray_color_t() ); unsigned char v4 = get_color( p4, gray_color_t() ); unsigned char v5 = get_color( p5, gray_color_t() ); unsigned char v6 = get_color( p6, gray_color_t() ); unsigned char v7 = get_color( p7, gray_color_t() ); unsigned char v8 = get_color( p8, gray_color_t() ); // all values should be 110b ( 6 ); assert( v1 == 6 ); assert( v2 == 6 ); assert( v3 == 6 ); assert( v4 == 6 ); assert( v5 == 6 ); assert( v6 == 6 ); assert( v7 == 6 ); assert( v8 == 6 ); return 0; } Thanks a lot, Christian