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From: mark@calvin..westford.ccur.com (Mark Thompson)
Newsgroups: comp.graphics
Subject: Re: IFF 24 bit images
Keywords: question
Message-ID: <61538@masscomp.ccur.com>
Date: 13 Dec 90 16:48:05 GMT
References: <18648@netcom.UUCP>
Sender: news@masscomp.ccur.com
Reply-To: mark@calvin.westford.ccur.com (Mark Thompson)
Organization: Concurrent Computer Corp. Westford MA.
Lines: 62

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?

I have modified the ilbmtoppm converter to handle IFF24 if this is of
interest to you. As for the format, it is basically identical to
the standard Amiga IFF accept that the bitplanes have been extended to
24 bit RGB as follows:

  IFF24 bit ordering for one scanline of an N width image

Pixel         0   1   2   3   4   5   . . . . . --> N

Scanline 0    R0  R0  R0  R0  R0  R0  . . . . .
              R1  R1  R1  R1  R1  R1  . . . . .
              R2  R2  R2  R2  R2  R2  . . . . .
              R3  R3  R3  R3  R3  R3  . . . . .
              R4  R4  R4  R4  R4  R4  . . . . .
              R5  R5  R5  R5  R5  R5  . . . . .
              R6  R6  R6  R6  R6  R6  . . . . .
              R7  R7  R7  R7  R7  R7  . . . . .

              G0  G0  G0  G0  G0  G0  . . . . .
              G1  G1  G1  G1  G1  G1  . . . . .
              G2  G2  G2  G2  G2  G2  . . . . .
              G3  G3  G3  G3  G3  G3  . . . . .
              G4  G4  G4  G4  G4  G4  . . . . .
              G5  G5  G5  G5  G5  G5  . . . . .
              G6  G6  G6  G6  G6  G6  . . . . .
              G7  G7  G7  G7  G7  G7  . . . . .

              B0  B0  B0  B0  B0  B0  . . . . .
              B1  B1  B1  B1  B1  B1  . . . . .
              B2  B2  B2  B2  B2  B2  . . . . .
              B3  B3  B3  B3  B3  B3  . . . . .
              B4  B4  B4  B4  B4  B4  . . . . .
              B5  B5  B5  B5  B5  B5  . . . . .
              B6  B6  B6  B6  B6  B6  . . . . .
              B7  B7  B7  B7  B7  B7  . . . . .

Scanline 1    . . . . . . . . . . . . . . . . . 
  .
  .

The storage sequence goes horizontally for each bit of the color
component by scanline width based on the above.
So the first byte in an IFF24 ILBM would represent 8 bits from the
first 8 least significant bits of red of the first horizontal 8 pixels:

  Pixel  0  1  2  3  4  5  6  7 --> N
        R0 R0 R0 R0 R0 R0 R0 R0  = first byte in the body CHUNK.

Hope this isn't too confusing! 
+--------------------------------------------------------------------------+
|  Mark Thompson                                                           |
|  mark@westford.ccur.com                                                  |
|  ...!{decvax,uunet}!masscomp!mark   Designing high performance graphics  |
|  (508)392-2480                      engines today for a better tomorrow. |
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