EnigmA Amiga Run 1995 October/EnigmA AMIGA RUN 01 (1995)(G.R. Edizioni)(IT)[!][issue 1995-10][Aminet 7].iso/Aminet/dev/amos/AMOSL0595.lzh/AMOSLIST/[e-mail]_Wed May 24 11:29:06 1995.msg

Internet Message Format | 1995-06-01 | 4KB

Received: from svcs1.digex.net by mail1.access.digex.net with SMTP id AA09001
  (5.67b8/IDA-1.5); Wed, 24 May 1995 11:29:05 -0400
Received: (from daemon@localhost) by svcs1.digex.net (8.6.12/8.6.12) id GAA16381 for amos-out; Wed, 24 May 1995 06:35:09 -0400
Received: from www1.access.digex.net (www1.access.digex.net [205.197.247.32]) by svcs1.digex.net (8.6.12/8.6.12) with SMTP id GAA16378 for <[e-mail]>; Wed, 24 May 1995 06:35:02 -0400
Received: from varano.ing.unico.it by www1.access.digex.net with SMTP id AA28304
  (5.67b8/IDA-1.5 for <[e-mail]>); Wed, 24 May 1995 06:33:07 -0400
Received: by varano.ing.unico.it (5.65/DEC-Ultrix/4.3)
    id AA06166; Wed, 24 May 1995 12:32:22 +0200
Date: Wed, 24 May 1995 12:32:22 +0200 (MET DST)
From: MeF <[e-mail]>
Subject: Re: point and Ham
To: Robert Currie <[e-mail]>
Cc: [e-mail], [e-mail]
In-Reply-To: <[e-mail]>
Message-Id: <[e-mail]>
Mime-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Status: RO
X-Status:



>     The way HAM works is that the first pixel of every line defines a
> color. The pixel beside it changes only one aspect of that color, either the
> red, green or blue aspect. This pattern is repeated across the entire line
> of  the graphics screen, each pixel only containing the change in one aspect pf
> the color. By getting the pixel color, you are really only getting the value
> of the change in one aspect of the previouse color. To calculate the color you
> must actually apply the changes made to the first pixel of the line up to and
> including the pixel in question. I am not sure of the exact form of the changes
> as in which change goes in which order(I think it is Red then Green then Blue)
> but I am sure someone could supply you with that information.

That's not precise.
It is not the firs pixel on the screen which determine the colour...
otherwise you could not have black and withe on the same line.

The HAM works this way (for HAM6):

The HAM is based on the fact that real good picture have lots of shade
which can be "compressed" in less bits.
You have a base palette of 16 colors. Now, the screen is done by 6 planes
(thta's why HAM6!).
The color of a pixel is described as follows:
the first 4 bit of the pixel (the first 4 bit-planes) tell you which color
of the palette had to be used as the reference color.
The last 2 bits (last two bitplanes) carry these informations:
If both bits are 00 the color is used pure that's you see the same color
which is stored in the palette base.
If I remember right the following value refer to RGB shades as follows...
If bit 1 is set to 1 you have a shade in the RED value of the color.
If bit 2 is set to 1 you have a shade in the GREEN value of the color
IF bit 1 is set to 1 and bit 2 is sey to 1 you have a shade in the BLUE
value of the color.

So a pixel can different from the next on the left only of a single
component of the color or it have to belong to the base palette set.

That's why you can't have smooth horizontal grey shades (but you can have
smooth horizontal red, blue, green shades). A grey shade implies you
firstly pass through the RED, the GREEN and the BLUE shade to finally
reach the desired grey shade.
That is there are two pixels on the screen which are not of the desired
color... that's called fringing.

Hope this will help.

MeF