
   Module name:   BRIGHTEN.MDL 
   Module I.D.:   BRIG (BRIGhten) 
   Module type:   Function module for colour images
   Author:        Dirk Haun @ WI2
   Status:        Freeware
   Version No:    0.04
   Version date:  23.07.1996
   Purpose:       Altering the brightness of colour images 


Description:

With this module one can alter the brightness of colour images. In the 
'Apply module...' dialog you can select from several pre-set values 
(5, 25 or 33 % lighter or darker). 'Select 1 - 99%', on the other hand, 
brings up a sub-dialog where you can freely select any value between 
1 and 99 % (0% is meaningless and will be rejected); after inputting 
the desired value, a click on the 'Lighter' or 'Darker' button (whichever 
you want) will alter the image, or you can click on 'Cancel' if you 
change your mind, in which case the picture will remain unaltered. 
Note that if you want the altered picture to appear in a new window rather 
than overwriting the old one, you have to click on the appropriate button 
_before_ you open the sub-dialog!

For the technically interested: The module converts the RGB colour values 
of the picture into YIQ colour space (where 'Y' is the brightness and 'I' 
and 'Q' the colour information). After this the Y-values are increased or 
reduced by the desired percentage and finally converted back to RGB colour 
space.

The YIQ-colour model is used, for instance, by the American NTSC television 
system. You will find further information about this in:

'Computer Graphics - Principles and Practice'
Foley, van Dam, Feiner, Hughes
Addison-Wesley, 1990
ISBN 0-201-12110-7


Standard disclaimer:

This module fulfils its objects for me, which does not mean that 
it will do this everywhere. So should one of these modules do
something unexpected, I cannot be held responsible for any sort
of damage caused thereby (whatever it may be) -- you use it at
your own risk.


Contact address:

The author of this module can be reached in the following ways:

 By snail-mail:

   Dirk Haun
   Europastr. 8
   64569 Nauheim

 By e-mail:

   Dirk Haun @ WI2 (MausNet)

