Xref: utzoo comp.windows.x:35595 comp.graphics:17434
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uupsi!sunic!dkuug!modulex!ssn
From: ssn@modulex.dk (Svend Skafte Nielsen)
Newsgroups: comp.windows.x,comp.graphics
Subject: Re: changing color intensity in X
Message-ID: <728@modulex.dk>
Date: 23 Apr 91 09:11:37 GMT
References: <1991Apr20.204325.2078@eng.ufl.edu>
Organization: A/S MODULEX, Copenhagen, Denmark
Lines: 40

tsao@helios.tcad.ee.ufl.edu ( Tsao) writes:


>	I am writing a graphics program for shading, would somebody tell me how to
>change the intensity of the same color like 'setgray' in postscript ? or the
>only way to do that is using different colors (blue, light blue, etc).

>	thanks.


>--

>--- Qing

   Intensity (also called lightness or luminance) is usually calculated
   as

         I = (R+G+B)/3

   where R, G and B are the resp. red, green and blue components of the
   color (e.g. from the XColor structure). 
   One way of changing the intensity of a color then is to increase or
   decrease each RGB component with an equal ammount. 
   A better way is to use a conversion of RGB to IHS values ( Intesity,
   Hue and Saturation), change I and transform back to RGB. 
   There are several books and articles on the subject e.g. Durrett: 
   "Color and Computers", John Rankin (I don't remember the title),
   Wayne Niblack: "Digital Image Processing".

   Good luck

   Svend.


---------------------------------------------------
Svend Skafte Nielsen    | Email:    ssn@modulex.dk
A/S MODULEX		| Phone:    +45 44 53 30 11
Lyskaer 15		| Telefax:  +45 44 53 30 74
DK-2730 Herlev		|
Denmark			|