Chagall Reference   Display   <Control-Z>  12.5.93
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   This dialog permits the setting of those 
   parameters that influence the display <Control-Z>
   of pictures in Chagall:

   'Show'
     Here you can choose whether normally only the
     picture, only the mask or both should be 
     displayed on the screen. You can also select
     this via the Function-keys <F8>, <F9>, <F10> 
     respectively.

   'Raster type'
     determines whether pictures having a greater
     colour-depth than that of the current screen
     resolution are to be displayed rastered or
     not ('No raster'). Colour pictures can be
     either unrastered, or use one specific raster.
    
     If you decide for an unrastered display, then
     the display quality may suffer badly in some 
     circumstances: 
     In the most favourable case the colours will
     simply appear with somewhat coarser gradations,
     but in unfavourable cases you may hardly be able
     to recognise anything on the screen! If you work 
     on a screen with less that 24-bit colour-depth
     then you should practically always select one 
     of the rastering algorithms.

     If you have decided on rastering, then Chagall
     offers several different rastering or dithering
     processes, of which two were developed specially 
     for screen display:
    
    'Ordered Dither'
       produces a very homogeneous, but artificial-
       looking pattern, while
    'Floyd-Steinberg' 
       produces a natural and more randomly-constructed
       pattern. In general FloydSteinberg is well suited
       for producing as natural-looking an impression  
       of the picture as possible, though Ordered Dither 
       is to be preferred for editing, since with this
       it is easier to keep a close check on the effect
       of any alterations.

     If you are working on a monochrome screen or with a 
     1-bit deep 'line' picture, then all raster types are 
     available and can be mixed in one picture. This 
     leaves open many design possibilities since the 
     drawing tools also use these rastering processes 
     in a monochrome picture.

   'Mask-colour'
     The mask-colour setting decides in which colour 
     the mask should be superimposed over the picture.
     Whereas in most cases one can work well with the
     (default) black mask, this option offers a way
     of overcoming difficulties if a black mask is
     hard to see (on a dark picture, for instance).
     If you click on the colour field then you can 
     select the colour directly from a PopUp. (This
     option is of little use on a monochrome screen
     since only solid black and white is available).
    
   'Display' 
     Here you can configure Chagall's display of 
     pictures:
     You should always activate 'Compatibility' when
     using a graphics card that arranges the colour
     information for a single pixel in a manner 
     that differs from normal. In our experience
     Chagall works reliably with 'Compatibility'
     switched off in practically all monochrome 
     resolutions and also with most graphics cards.
     When using built-in TT and Falcon resolutions,
     however, then for 16- and 256-colour graphics 
     modes 'Compatibility' must be switched on.
     Incidentally, Chagall attempts to recognise
     automatically when 'Compatibility' has to be
     switched on, so that in most cases you don't 
     need to bother about its operation.
  
   'Use cache'
     You should switch on the 'Use cache' option
     particularly if you use Chagall without a  
     True-Color graphics card and nevertheless 
     wish to edit colour pictures:
     Chagall will then try to create a cache for
     every picture, as long as sufficient RAM 
     memory is available. This cache ensures an
     appreciably faster screen redraw, specially
     when the contents of a window have to be
     built up anew (e.g. when moving a picture).
     In principle the cache will lead to a minimal
     slowing down during drawing, though this is
     hardly noticeable.
     
   'Color model'
     determines in which colour system (RGB, YMC or 
     HSB) Chagall will input and show colours.
     Which model is to be preferred depends on the
     use to which the picture is to be put.

