Chagall Reference   Mask                  12.5.93
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   Masks act as a stencil that one can lay over
   a picture while editing (working on) it so
   as to restrict the effect of an operation to 
   a defined, unmasked region. 

   While in 'real life' one can mostly only resort 
   to stencils working digitally, Chagall's masks
   work in an analogue manner:

   A digital stencil has only two values, that is
   full operation or none. The masks in Chagall, 
   however, have 256 shades available, so that with 
   the help of a mask one can graduate the effect 
   of an operation, i.e. a tool or a filter for 
   instance, in different parts of the picture.

   A mask is practically a halftone picture that
   lies over the actual picture. White areas of
   the mask let the effects of an operation that
   respects the mask pass without hindrance, so
   that it will operate at full strength. The 
   darker the mask is at a given point, however, 
   the less effect the operation will have at that
   point.  Thus black areas of the mask result in
   the corresponding operation having no effect 
   at all in that region.

   In Chagall all tools and filters are constructed
   so that their intensity (strength of effect) can
   be controled with a mask.

   In each dialog it is possible to choose whether 
   the effect will respect the mask or not.

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  |  Create new maskCREATE  |    Invert maskINVERT    |   Apply maskAPPLY     |
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  |     Save maskSAVE     |    Load maskLOAD      | Mask over colourCOLOR |
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  |  Mask in PictureMSK2PIC  |  Picture in MaskPIC2MASK  |   Delete maskDELETE    |
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