Chagall Reference   Mask over colour       12.5.93
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   'Mask over colour' makes it possible to generate
   a mask automatically from a selectable colour or
   range of colours.
   
   To do this you click on 'Define' and place the 
   resultant cross on a point whose colour will be
   used as a reference for generating the mask. The
   colour values of the chosen point will be displayed
   under 'Fill-range'. You quit the selection with a
   right mouse click. Alternatively you can click on
   the colour values, clear the resultant field with
   <Esc> and type in new figures. As a third possibility
   you can click on the colour patch which brings up a
   dialog box containing a colour square in which you can
   click on the required colour, or again use sliders, 
   their arrows or the digital display. See Colour selection..\TOOL\COLORBOX.
   
   As in the case of area fill, you can also specify a 
   tolerance range for this function for the individual 
   basic colours of the current colour-model.
   
   'Mask over colour' then generates a mask that is
   black in those places that are included in the 
   specified colour range.  If the 'Apply mask' entry is 
   active, then the newly created mask region will be 
   added to the existing one, i.e. the previously created 
   mask will remain. If the entry is not active then the 
   existing mask will be cleared completely before the new 
   mask region is created.

   The additional 'Magic wand' option (again as in the 
   case of the fill function) ensures that the selection 
   of the chosen colour range starts from a given point 
   and only includes those parts of the picture that lie 
   within the given colour range and are also adjacent to 
   the start-point. For this the mouse cursor appears as
   a funnel with which you can set the starting point 
   before the function is carried out. In this case there
   is, of course, no point in defining a starting colour, 
   since this is determined automatically by the mouse 
   click when executing the function.

   WARNING: Since when filling via the 'Magic wand' it 
   is always just the rectangle on the screen which has 
   really been filled that is re-drawn, it is possible 
   that with the 'Apply mask' option deactivated the 
   previous mask regions will still be displayed on the
   screen even though the mask has been cleared. In this 
   case you should, after ending the function, press the
   <Clr Home> key once to see the correct mask.

   If when selecting this function no mask is present, 
   then this will be created automatically.

   A typical application of the 'Mask over colour' 
   function is for modifying certain parts of a picture 
   that have a similar colour. One can easily generate 
   a mask with the function that isolates a single 
   object in the picture, and thus protects it from
   any changes made in the editing process.

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