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From: her@compel.UUCP (Helge Egelund Rasmussen)
Newsgroups: comp.sys.amiga
Subject: Re: HAM-E
Message-ID: <1233@compel.UUCP>
Date: 22 Oct 90 11:12:58 GMT
References: <34115@nigel.ee.udel.edu>
Organization: Compel, Copenhagen, DK
Lines: 51

JK829055@pucal.bitnet (Jim Karczewski, Programmer -- TTR Development, Inc.) writes:

>Actually when you are painting on a 320x400 Picture.. it is a 640x400 Picture
>Compressed.. So that gives you up to 16,192 Colors per screen at once.. Seeing
>that you have 2 Pixels of information for ever one pixel displayed
>on the screen.  But this still doesn't make sense to me because there is the
>limit of 16 colors on a Hi-Res screen..

>                                        Jim Karczewski

I've just received my HAM-E, and I like it very much (it really works :-) ).

Here is a description of the way HAM-E works (as far as I understand):

HAM-E concatenates two pixels in a HIRES picture (640xwhatever) to form a
8 bit pixel in LORES (320xwhatever). This mean, that there is 8 bits to 
describe every pixel.

HAM-E can use this info in two ways:

1: Register mode.
  In this mode the 8 bits is used as a color index, ie. a pointer to a color 
  table with 256 entries (each entry in the color table is described with 24 
  bit). 
  In this mode you can use 256 colors from a palette consisting of 2**24
  colors = 16,777,216 colors).
  This is like normal amiga hires mode where you can use 16 colors from a 
  palette consisting of 2**12 = 4096 colors.
  The paint program uses this mode.

2: Ham mode.
  In this mode the 8 bits is used like the normal Amiga HAM mode. That is
  2 bits are used for choosing which color (R, G or B) to change, and 6 bits 
  are used for the new color value. 
  This gives 2**18 colors = 262144 colors, on the screen at the same time.
  Of course you have the same "fringing" problems as the normal Amiga HAM mode,
  but as you have 2**6 = 64 color registers to use, the problem is much smaller
  than in normal HAM mode. 
  The above description is not the full story, in fact you have 250 color
  registers in HAM mode so the problem is even smaller.

Every HAM-E picture must start with one or more scanlines which contains
the values for the color registers, and an indication of which mode to use.
But otherwise the pictures is just like any other HIRES picture, that is 
you can use any IFF viewer to show HAM-E pictures.

---

Helge E. Rasmussen  .  PHONE + 45 31 37 11 00  .  E-mail:  her@compel.dk
Compel A/S          .  FAX   + 45 31 37 06 44  .  
Copenhagen, Denmark