glBindBuffer( GL_PIXEL_PACK_BUFFER_ARB, pbo->pbo );
check_error();
glBufferData( GL_PIXEL_PACK_BUFFER_ARB, img_size, NULL, GL_STREAM_READ );
glBindBuffer( GL_PIXEL_PACK_BUFFER_ARB, pbo->pbo );
check_error();
glBufferData( GL_PIXEL_PACK_BUFFER_ARB, img_size, NULL, GL_STREAM_READ );