Path: utzoo!utgpu!attcan!uunet!lll-winken!ames!pacbell!well!pokey
From: pokey@well.UUCP (Jef Poskanzer)
Newsgroups: comp.graphics
Subject: Re: the word "bitmap"
Message-ID: <10354@well.UUCP>
Date: 14 Jan 89 23:30:35 GMT
References: <975@etnibsd.UUCP>
Reply-To: Jef Poskanzer <jef@rtsg.ee.lbl.gov>
Organization: Paratheo-Anametamystikhood Of Eris Esoteric, Ada Lovelace Cabal
Lines: 27

I get a lot of mail about my portable bitmap toolkit.  I mean a *lot*
of mail - I'm approaching 1000 messages.  A certain percentage of the
mail has always asked how come the package barfs when fed a color
image.  Now, I named the package specifically to avoid this class of
questions.  I thought *everyone* knew that a bitmap is one bit deep.
Apparently not.

The origin of the term bitmap has to do with there being a mapping, in
the strictest mathematical sense, between bits in memory and pixels on
the screen.  The bits don't have to be currently displayed to qualify;
the mapping is still there even when not being used.  Remember, bitmap
screens were a new idea back then - memory was $thousands / K, the
PDP-11 (memory-mapped I/O) had just been invented, and most displays
were vector-based.

It is hard for me to see how you can get from this origin to using
"bitmap" for grayscale and color images.  I agree that the terminology
is still evolving in this area.  Thanks to the X folks, "pixmap" is
becoming common for color images.  But I haven't yet heard anyone use
an analogous term for grayscale.  So I'll propose one: "graymap".

Now, is everybody happy?
---
Jef

             Jef Poskanzer   jef@rtsg.ee.lbl.gov   ...well!pokey
                                 Actual size.