more for #252 (load pixel mask); explain background peaks for scripting

Author: briantoby

GSASII/GSASIIimgGUI.py

@@ -2044,10 +2044,12 @@ def OnLoadPixelMask(event):
                                              # was loaded rather than a search
         data['SpotMask']['spotMask'] = maskImage > 0
         nmasked = sum(data['SpotMask']['spotMask'].flatten())
-        frac = nmasked/data['SpotMask']['spotMask'].size
+        frac = 100*nmasked/data['SpotMask']['spotMask'].size
         G2G.G2MessageBox(G2frame,
                              f'Mask removes {nmasked} pixels ({frac:.3f}%)',
                              'Mask loaded')
+        wx.CallAfter(UpdateMasks,G2frame,data)
+        wx.CallAfter(G2plt.PlotExposedImage,G2frame,event=event)
 
     def OnFindPixelMask(event):
         '''Do auto search for pixels to mask

GSASII/GSASIIscriptable.py

@@ -3494,12 +3494,25 @@ def Background(self):
     def add_back_peak(self,pos,int,sig,gam,refflags=[]):
         '''Adds a background peak to the Background parameters
 
+        Background in diffraction patterns is usually fit 
+        with a slowly varying smooth function, such as a Chebyschev
+        polynomial, but when the background contains broad peaks
+        (for example from a Kapton sample container) those peaks
+        are usually better fit by adding extra peaks to the
+        smooth background function rather that providing enough 
+        parameters to the smooth function in order fit the
+        peak(s). Note that background peaks are typically treated 
+        as Gaussian only (``gam``=0) with very large ``sig`` 
+        values (>1000). Normally one should refine ``int`` and 
+        then ``sig`` and only after the background peak is well 
+        fit can one refine the ``pos`` value. 
+
         :param float pos: position of peak, a 2theta or TOF value
         :param float int: integrated intensity of background peak, usually large
         :param float sig: Gaussian width of background peak, usually large
-        :param float gam: Lorentzian width of background peak, usually unused (small)
+        :param float gam: Lorentzian width of background peak, usually not used (small)
         :param list refflags: a list of 1 to 4 boolean refinement flags for
-            pos,int,sig & gam, respectively (use [0,1] to refine int only).
+            pos,int,sig & gam, respectively (e.g. use [0,1] to refine int only).
             Defaults to [] which means nothing is refined.
         '''
         if 'peaksList' not in self.Background[1]: