walk_pos[0] = image_conv_alpha_func(walk_sec_pos[0], walk_sec_pos[src->channels - 1], a[0], b[0]); \
walk_pos[1] = image_conv_alpha_func(walk_sec_pos[1], walk_sec_pos[src->channels - 1], a[1], b[1]); \
walk_pos[2] = image_conv_alpha_func(walk_sec_pos[2], walk_sec_pos[src->channels - 1], a[2], b[2]); }while(0)
walk_pos[0] = image_conv_alpha_func(walk_sec_pos[0], walk_sec_pos[src->channels - 1], a[0], b[0]); \
walk_pos[1] = image_conv_alpha_func(walk_sec_pos[1], walk_sec_pos[src->channels - 1], a[1], b[1]); \
walk_pos[2] = image_conv_alpha_func(walk_sec_pos[2], walk_sec_pos[src->channels - 1], a[2], b[2]); }while(0)