Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!sdd.hp.com!uakari.primate.wisc.edu!dali.cs.montana.edu!masscomp!peora!tarpit!bilver!alex
From: alex@bilver.uucp (Alex Matulich)
Newsgroups: comp.sys.amiga.graphics
Subject: Re: GreyScale Questions
Message-ID: <1991Feb23.174113.18677@bilver.uucp>
Date: 23 Feb 91 17:41:13 GMT
References: <4868@mindlink.UUCP>
Organization: W. J. Vermillion - Winter Park, FL
Lines: 37

In article <4868@mindlink.UUCP> Harvey_Taylor@mindlink.UUCP (Harvey Taylor) writes:
>    It seems the maximum greyscale range I can get is 16. Why? It seems
> to me I should be able to get 32 using EHB mode. Yes? No?

No.  The Amiga video hardware only allows 16 intensity levels for the
red, green, and blue electron guns in the CRT.  You will notice in your
palette setup that there are 4 bits per gun, which means 16 levels.

Extra half-brite will not help you here.  EHB can NOT increase the number
of available colors above the 4,096 you already have.  EHB will give you
a second set of colors that are half the brightness of the first set, but
the second set are still within the original 4,096 color range.  So, if
you already have the 16 gray levels

000,111,222,333,444,555,666,777,888,999,aaa,bbb,ccc,ddd,eee,fff

then EHB will give you these "additional" colors which will be repeats
of the ones above:

000,000,111,111,222,222,333,333,444,444,555,555,666,666,777,777

The only way I have ever been able to increase the number of gray levels
is to use dithering.  It's trivial to do with fill masks, and the results
are VERY nice in hi-res mode.

>    In the A2024 docs [in the autodocs] this formula occurs:
>*       Gray Level = (77 * R + 150 * G + 29 * B + 128)/1024
>    What is the basis for this?

This formula approximates the NTSC formula for converting color to
black & white.

-- 
 _ |__  Alex Matulich   (alex@bilver.UUCP)
 /(+__>  Unicorn Research Corp, 4621 N Landmark Dr, Orlando, FL 32817
//| \     UUCP:  ...uunet!tarpit!bilver!alex
///__)     bitnet:  IN%"bilver!alex@uunet.uu.net"