27 : file(file), gain(0.), saturation(0.), flux_scale(1.), psf_file(psf_file), weight_file(weight_file),
28 weight_absolute(false), weight_scaling(0.), has_weight_threshold(false), weight_threshold(0.),
29 is_background_constant(false), constant_background_value(0.), image_hdu(0), psf_hdu(0), weight_hdu(0) {