Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!samsung!think.com!mintaka!wookumz.ai.mit.edu!rjc
From: rjc@wookumz.ai.mit.edu (Ray Cromwell)
Newsgroups: comp.graphics
Subject: Re: IFF 24 bit images
Keywords: question
Message-ID: <1990Dec13.033315.2560@mintaka.lcs.mit.edu>
Date: 13 Dec 90 03:33:15 GMT
References: <18648@netcom.UUCP>
Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius)
Organization: None
Lines: 32

In article <18648@netcom.UUCP> allanh@netcom.UUCP (Allan N. Hessenflow) writes:
>I'm looking for information on the format of IFF 24 bit images.  I have
>PBM & FBM, both of which will read IFF ILBM ham mode images; while I was
>looking for sample images to test a reader in ham mode I kept finding
>images which claim to be "IFF 24 bit images."  While I'm asking, are there
>any other types of IFF images besides 1-8 bit mapped, ham, and 24 bit?

  Yes and quite a few. First, because of the Amiga's display coprocessor
(COPPER) there are some IFF Formats that overcome the Amiga's pallete
limitations (32 registers non-ham) by reloading the palette every scanline.
Among these are SHAM(Sliced HAM), AHAM & DHAM (Dynamic Ham, basically
they are almost identical to SHAM except for the chunk names being
different. These 2 were invented by ASDG & Newtek) Although I don't have
all the information availible, I know a little about them that can help.
SHAM format is almost the same as ILBM except that it has an extra chunk
called CTBL (I think) This chunk contains a palette for each scanline.
(the AHAM and DHAM formats changed the name of this to something else)
There is also an ARES format (and DRES too, or whatever Newtek calls it)
In this mode, you have a normal hi-res interlaced picture, but with
a seperate palette every scanline. NewTek has an IFF21? (21 bit format)
also (I think its obsolete now) that they used on Digiview 3.0.
You might try looking on bix, or ftping shamview from abcfd20.larc.nasa.gov.
some of the people on comp.sys.amiga can help too, Like Perry from ASDG
software. (sorry, I can't remember how to spell his last name.)

It would be great to have pbm support SHAM/DYnamic Hires modes, but
I scanline by scanline quantizer would be needed. (since the base palette
can be changed every scanline.)

>allan
>-- 
>Allan N. Hessenflow   {apple|claris}!netcom!allanh    allanh@netcom.uucp