Chagall Reference     Filters              12.5.93
==================================================

   With filters you can change certain properties of
   a picture automatically in numerous ways.

   Chagall differentiates between two filter types:
   Those that may be applied to colour and halftone
   pictures and those that are available only for
   monochrome pictures.

   The following colour/halftone filters are 
   available in Chagall:

   - 'Sharpen':
     This reinforces the contours in the picture.
     One should use this filter with restraint 
     (by choosing a low 'Factor' for 'Effectiveness')
     or use the 'Smooth/sharpen' option instead.

   - 'Smooth/sharpen':
     A combination of 'Sharpen' and 'Smoothe'. This
     filter is particularly suited to sharpening
     a picture if you wish to avoid unnaturally
     hard contours.

   - 'Smoothe':
     Eliminates small variations of colour (noise)
     in a picture. Contours will be respectably 
     smoothed without smudging them.

   - 'Smudge':
     Adjacent picture portions will be smudged, so
     that contours are softened.

   - 'Invert':
     The picture will be transformed into its  
     negative (with tones and colours reversed).
     With this filter 'Effectiveness' has no meaning.

   - 'Relief':
     An effect-filter, which makes the picture look as
     if it had been pressed into soft metal. The 
     'Effectiveness' slider regulates the amount of
     blending with the original.
       
   - 'Mosaic':
     Here you can 'disintegrate' a picture into a mosaic.
     The 'Effectiveness' slider serves here for setting
     the size of the individual mosaic 'tiles'.

   The 'Effectiveness' factor normally determines the
   strength of the changes that the respective filter 
   makes to the picture. Which values are sensible here 
   depends not only on the filter itself, but also on
   the picture and the desired effect.

   For modifying a monochrome picture Chagall offers the
   following monochrome filters:

   - 'Outlin'e:
     Forms contours

   - 'Thin out':
     Reduction of pixel accumulation (erosion).

   - 'Thicken':
     Increase of pixel accumulation (dilatation).

   - 'Pixelfilter':
     Removes individual pixels.

   - 'Roughen':
     A combination of erosion and dilatation.
     This function can only be used once on a
     picture.

   - 'Smoothe':
     Another combination of dilatation and erosion 
     in different proportions. Again, this function 
     can only be used once on a picture.

   Naturally Chagall also permits restricting the 
   effective range of the filters, so that only a
   cut-out or a masked region can be selected for 
   sharpening, for instance. 

   Finally it should be noted that all filters use  
   mathematically-intensive operations and hence
   take some time to calculate. If you have second
   thoughts while waiting, you can break off any
   filtering operation with a <Shift-Shift> key 
   combination.

