Chagall Reference   Change colour-space    12.5.93
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   'Change colour-space' is a powerful but also
   a very complex function. It serves to replace
   a given group of colours by others. So one
   can change the colour of an object consisting
   of many nuances of a given colour without 
   having to look after each individual shade.
   Thus one can easily transform a red pepper 
   into a green or red one.

   To do this one has to set a colour-centre for 
   the source and the goal (target) picture. It 
   is normal to use the HSB colour model for 
   setting the colour in each case.

   Quick changes can be made by dragging the 
   respective sliders; the values will be shown 
   on the right. More accurate adjustment is
   possible by clicking on the arrows, or on the
   readout value which will bring up a numerical
   field that you can clear with <Esc> and type
   in the new value. Note that as with all similar 
   numerical fields you have to use the existing
   decimal point; it CANNOT be typed in!

   As an alternative you can also call up a 
   colour selector..\TOOL\COLORBOX that shows the available 
   range of colours more graphically by clicking 
   on the colour patch next to 'Source' or 'Goal'; 
   here you again have the choice of dragging 
   the sliders or inputting values numerically, 
   and you can also set the colour by clicking 
   in the graduated display, which uses the 
   currently active colour model.

   Besides the colour-centre you also have to
   preset a tolerance value which defines the 
   maximum permitted deviation of the H (hue),
   S (saturation) and B (brightness) values from
   the source colour-centre. Again you can use
   the arrows or click on the numbers for numerical 
   input.

   With values of 0% only the exactly defined 
   source colour will be replaced, with higher
   values correspondingly more divergent colours.

   With 'Pick' it is possible to choose the source
   in a simpler manner. To do this you run over the 
   picture with a small square that appears after a
   click on the 'Pick' button, and then you can 
   collect the source colour-space piece by piece.
   Since you can repeatedly start at a different 
   place with a new mouse click, you have to quit
   this function explicitly with a right mouse-click.
   The 'Change colour-space' function pays regard 
   to Masks..\MASK\MASK, if the corresponding option is
   switched on, whereby its effect is reduced in
   proportion to the mask density.

   The operating range can be restricted to a frame.

