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From: aaron@madnix.UUCP (Aaron Avery)
Newsgroups: comp.sys.amiga.tech
Subject: Re: 24bit/pixel
Message-ID: <954@madnix.UUCP>
Date: 4 Nov 89 06:29:27 GMT
References: <5342@spudge.UUCP>
Reply-To: aaron@madnix.UUCP (Aaron Avery)
Organization: ASDG Incorporated
Lines: 38

In article <5342@spudge.UUCP> johnm@spudge.UUCP (John Munsch) writes:
>What is the official IFF format for 24bit/pixel pictures?  Is it just a
>FORM ILBM with 24 interleaved bitplanes, no CMAP, and some decree that 
>(for example) the first 8 planes represent the red component the next 8
>green, etc.  Actually, I kind of hope not, because bitplanes work great for
>the Amiga's display but they are an awful way to store that data for other
>work.

Yes. That's basically it. 

Yes, it's a pain to do image processing unless the data is in chunky pixel
format, but also, many current graphics processors allow you to specify
bitplane or chunky format for the display.  Also, 24-bit files stored in
bitplane format compress quite well, due to the equally-significant bits
being stored together.

As to the standard...
Store a BMHD indicating 24 bitplanes. No CMAP, but don't bomb if you find
one; just ignore it. Within the BODY, the bitplane ordering is as follows:

bit 0 of red   ...   bit 7 of red
bit 0 of green ... bit 7 of green
bit 0 of blue  ...  bit 7 of blue

Thus, any reader which can currently deal with an 8-bit ILBM, should have
no trouble, as the bitplanes are in the same order as an 8-bit ILBM would
be, for each of red, green and blue.

This can also be extended to fewer bitplanes, such as 18, as long as it's
divisible by 3.

- Aaron

-- 
Aaron Avery, ASDG Inc.         "A mime is a terrible thing to waste."
                                                             -- Robin Williams
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