allow normalizing extracted bg spectrum per-spaxel

jdaviz/configs/cubeviz/plugins/spectral_extraction/spectral_extraction.py

@@ -56,7 +56,12 @@ class SpectralExtraction(PluginTemplateMixin, ApertureSubsetSelectMixin,
       Whether the ``background`` aperture should be considered wavelength-dependent (requires
       ``wavelength_dependent`` to also be set to ``True``). The cone is defined
       to intersect ``background`` at ``reference_spectral_value``.
+    * ```bg_spec_per_spaxel``:
+        Whether to normalize the resulting summed background per spaxel when calling
+        ``extract_bg_spectrum``.  Otherwise, the spectrum will be scaled by the ratio between the
+        areas of the aperture and the background aperture. Only applicable if ``function`` is 'Sum'.
     * ``bg_spec_add_results`` (:class:`~jdaviz.core.template_mixin.AddResults`)
+    * :meth:`extract_bg_spectrum`
     * ``aperture_method`` (:class:`~jdaviz.core.template_mixin.SelectPluginComponent`):
       Method to use for extracting spectrum (and background, if applicable).
     * ``add_results`` (:class:`~jdaviz.core.template_mixin.AddResults`)
@@ -78,6 +83,7 @@ class SpectralExtraction(PluginTemplateMixin, ApertureSubsetSelectMixin,
     bg_scale_factor = Float(1).tag(sync=True)
     bg_wavelength_dependent = Bool(False).tag(sync=True)
 
+    bg_spec_per_spaxel = Bool(False).tag(sync=True)
     bg_spec_results_label = Unicode().tag(sync=True)
     bg_spec_results_label_default = Unicode().tag(sync=True)
     bg_spec_results_label_auto = Bool(True).tag(sync=True)
@@ -184,7 +190,7 @@ def __init__(self, *args, **kwargs):
     def user_api(self):
         expose = ['dataset', 'function', 'aperture',
                   'background', 'bg_wavelength_dependent',
-                  'bg_spec_add_results', 'extract_bg_spectrum',
+                  'bg_spec_per_spaxel', 'bg_spec_add_results', 'extract_bg_spectrum',
                   'add_results', 'extract',
                   'wavelength_dependent', 'reference_spectral_value',
                   'aperture_method']
@@ -472,7 +478,7 @@ def extract(self, return_bg=False, add_data=True, **kwargs):
                                            self.wavelength_dependent,
                                            selected_func, **kwargs)
 
-        bg_spec = self.extract_bg_spectrum(add_data=False)
+        bg_spec = self.extract_bg_spectrum(add_data=False, bg_spec_per_spaxel=False)
         if bg_spec is not None:
             spec = spec - bg_spec
 
@@ -518,15 +524,20 @@ def extract_bg_spectrum(self, add_data=False, **kwargs):
             Additional keyword arguments passed to the NDDataArray collapse operation.
             Examples include ``propagate_uncertainties`` and ``operation_ignores_mask``.
         """
+        # allow internal calls to override the behavior of the bg_spec_per_spaxel traitlet
+        bg_spec_per_spaxel = kwargs.pop('bg_spec_per_spaxel', self.bg_spec_per_spaxel)
         if self.background.selected != self.background.default_text:
             bg_spec = self._extract_from_aperture(self.spectral_cube, self.uncert_cube,
                                                   self.background, self.bg_weight_mask,
                                                   self.bg_wavelength_dependent,
                                                   self.function_selected.lower(), **kwargs)
             if self.function_selected.lower() == 'sum':
-                # then scale according to aperture areas across the spectral axis (allowing for
-                # independent wavelength-dependence btwn the aperture and background)
-                bg_spec *= self.aperture_area_along_spectral / self.bg_area_along_spectral
+                if bg_spec_per_spaxel:
+                    bg_spec *= 1 / self.bg_area_along_spectral
+                else:
+                    # then scale according to aperture areas across the spectral axis (allowing for
+                    # independent wavelength-dependence btwn the aperture and background)
+                    bg_spec *= self.aperture_area_along_spectral / self.bg_area_along_spectral
         else:
             bg_spec = None
 

jdaviz/configs/cubeviz/plugins/spectral_extraction/spectral_extraction.vue

@@ -141,6 +141,14 @@
               <span style="padding: 6px">Export Background Spectrum</span>
             </v-expansion-panel-header>
             <v-expansion-panel-content class="plugin-expansion-panel-content">
+              <v-row v-if="function_selected === 'Sum'">
+                <v-switch
+                  v-model="bg_spec_per_spaxel"
+                  label="Normalize per-spaxel"
+                  hint="Whether to normalize the resulting summed background per spaxel (not shown in preview).  Otherwise, the spectrum will be scaled by the ratio between the areas of the aperture to the background aperture."
+                  persistent-hint
+                ></v-switch>
+              </v-row>
               <plugin-add-results
                 :label.sync="bg_spec_results_label"
                 :label_default="bg_spec_results_label_default"

jdaviz/configs/cubeviz/plugins/spectral_extraction/tests/test_spectral_extraction.py

@@ -343,6 +343,9 @@ def test_background_subtraction(cubeviz_helper, spectrum1d_cube_largest):
         assert extract_plg._obj.marks['bg_spec'].visible
 
         bg_spec = extract_plg.extract_bg_spectrum()
+        extract_plg.bg_spec_per_spaxel = True
+        bg_spec_normed = extract_plg.extract_bg_spectrum()
+        assert np.all(bg_spec_normed.flux.value < bg_spec.flux.value)
         spec = extract_plg.extract()
 
     assert np.allclose(spec.flux, spec_no_bg.flux - bg_spec.flux)