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Re: [OM] Photoshop7: Making a grey scale

Subject: Re: [OM] Photoshop7: Making a grey scale
From: Garth Wood <garth@xxxxxxxxxxxxxxx>
Date: Sun, 25 May 2003 13:00:58 -0600
At 02:38 PM 5/25/2003 -0400, Lama wrote:
>How do I make a simple grey scale that I can print out, then photograph?  If 
>tell PS to "Fill" something at 18%, then print it on my
>inkjet, will it match my store bought 18 0rey card or does "18%" in PS mean 
>something different?  What is the 8-bit equivalent of
>18% reflectance?  Obviously all the colors will be equal but what's the value 
>between 0 and 255?


Jim:

Well, there's a bunch of different ways you can do this.  PS7 allows you to use 
several different colour models (Lab, HSB, RGB, etc.).  In Lab and HSB, the 
values for 18 0rey (which is really 180f pure black, and the same thing as 820f 
pure white) are:


   L,a,b = 84, 0, 0
   
   H,S,B = 0, 0, 82

Or you can input the value as a RGB triplet, thusly:

   R,G,B = 209, 209, 209 (slightly off from 82% white, because [(256 x .82) - 
1] = 208.92 or approx. 209; close enough for jazz...)


Now, whether you can print this off and actually get a *real* 18 0rey depends 
on whether or not your printer's been calibrated.  Since I've never had to 
worry about this, I've never done it.  Others on this List know way more about 
printer calibration than I probably ever will.


Garth




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