Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!wuarchive!ukma!uflorida!mephisto!mcnc!rti!stdc01!mjones
From: mjones@stdc01.UUCP (Michael Jones)
Newsgroups: comp.graphics
Subject: Re: Converting grey scales to color
Message-ID: <582@stdc01.UUCP>
Date: 1 Dec 89 14:25:21 GMT
References: <128585@sun.Eng.Sun.COM>
Reply-To: mjones@stdc01.UUCP (Michael Jones)
Organization: Star Technologies, Graphicon Products Division (RTP, N.C)
Lines: 47

In article <128585@sun.Eng.Sun.COM> lyon@zeppy.Sun.COM (Lional Kendall) writes:
> I am looking for software that will convert grey scale pictures (.tiff)
> from my HP Scanjet back to their original colors.
> My scanner is presently connected to a 286AT, but I can connect it to 
> my Sun 386i if necessary.

I think that this is an honest question, so here is an honest answer:

1. You can't. The color information has been lost. Each monochrome 
   pixel value has been calculated by the scanner as 

       M = .30*R + .59*G + .11*B

   where R, G, and B are the "colors" in the original. (The scanner
   may not use the NTSC primaries, but this is the general scheme.)

   After this, you no longer know, when given M, what the R, G, and B
   values are. Perhaps Green was more, and Red was less ... or, else
   Green and Red were less, but Blue was much more, etc.

   Imagine a guessing game where player A (the scanner) says: "I have
   a number whose square is 4. Guess it!" and Player B (the person who 
   wants the color back) says "sqrt(4.0) -> 2.0 ... I guess two!". You
   may be suprised when player A sounds the jarring buzzer and shouts
   "NO! WRONG! The answer was negative two". The needed information was
   lost in the squaring, just as it is in scanning.

2. You might. But not in an automated, magic, manner. If you know what 
   colors (pixel chromaticities) were in your original image, then you
   will be able to supply the information that the scanner lost. If
   you think you know (i.e. are willing to guess), then you should talk
   to someone in the "Movie Colorization" industry. Suitable examples
   would be Color Systems Technologies, American Film Technologies,
   Colorization, Tintoretto, and Spectral Effects. I can steer you to
   the best technology for this task if you want to do it, but you
   really should try solution number three if you have access to the
   original color material.

3. You can. Buy a color scanner. Several are available, ranging from 
   the basic Mitsubishi SC-7500 (which is sitting beside me now), to 
   the very high quality scanners made by scitex and other prepress 
   groups. You might check out "Array Technologies"

-- 
-- Michael T. Jones          Email:    ...!{uunet,mcnc}!rti!stdc01!mjones --
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