Chagall Reference   Picture to mask       12.5.93
=================================================

   This function makes it possible to adopt the
   current picture as a mask for another picture.
   For this first select the corresponding picture,
   which naturally has to be a halftone image.
   Then select the 'Picture to mask' function. 
   The mouse cursor will change to a small window
   symbol, with which you click on that picture
   window to which you wish to assign the mask.

   The combination of 'Mask to new picture' and
   'Picture to mask' makes it possible to separate
   a mask from its picture in a moment, alter it
   separately and then continue using it as a mask.
   While Chagall of course permits direct editing
   of a mask in the mask mode, the procedure 
   described above has two advantages: 

   - A mask isolated as a picture can have its
     own mask applied to it in turn.
   - The mask will be displayed unrastered as a
     grey-scale.
