Path: utzoo!mnetor!uunet!husc6!endor!olson
From: olson@endor.harvard.edu (Eric K. Olson)
Newsgroups: comp.sys.mac
Subject: Re: Mac II Color Graphics Standard?
Message-ID: <3719@husc6.harvard.edu>
Date: 6 Jan 88 15:19:37 GMT
References: <7863@eleazar.Dartmouth.EDU>
Sender: news@husc6.harvard.edu
Reply-To: olson@endor.UUCP (Eric K. Olson)
Organization: Lexington Software Design
Lines: 60
Keywords: Mac II, Color

Unfortunately, there are many formats for color and/or grayscale information
generated on a Mac II:

	The most general way to move PICT 2 (Mac II PICT) data is via the
clipboard.  This allows any program that opens multi-bit windows to pass
color pictures in and out of itself.  It doesn't require any special file
type, so it is supported most easily.

	A PICT file contains the same information as a clipboard PICT, but
stored in the data fork of a file.  Pixelpaint supports this format.  Some
older Mac software (MacDraw) can also generate this type of file, but not
in color.

	A GrayView file contains the same information as a PICT file and a
clipboard PICT, but stored in a PICT #0 resource in the resource fork of the
file.  This is the format of a Mac II StartUpScreen, as well as a DeskPicture
for use with the DeskPict INIT.  If the file contains an original Mac-screen
size bitmap (uncompressed) in the data fork, that bitmap will be used as the
StartUpScreen on a non-Mac-II.

	The drawback of all the PICT formats is that they cannot be generated
easily on a non-Mac-II, and if PICT 2 data is displayed on a non-Mac-II, it
will be displayed as black & white, with white being > 50% luminance (the
same display you would get if you displayed them on a Mac II set to 2 color
mode).  For this reason, there are formats which can hold grayscale information
useable by non-Mac-II's, also:

	TIFF is a "standard" scanner format, which can hold either a huge
bitmap containing 100% black and 100% white pixels (data from scanners is
usually in this format-- but sometimes in greyscale), or a grayscale picture,
a PixMap (multi-bit-per-pixel BitMap) containing pixels varying in intensity
(usually 16 or 256 gray levels per pixel).  It can also represent color
information, but without a lookup table (gray data doesn't need a lookup
table as much), usually 2 bits each for red, green, and blue.  TIFF is an
extensible format, so software written a while ago sometimes cannot deal
with newer TIFF file (for instance, grayscale TIFF is newer than scanner TIFF).

	ThunderScan GrayMap format can represent up to 64 gray levels per
pixel.  I find it useful for backwards compatibility.  ImageStudio can read
this format.  Thunderscan can include a grayscale map (pixel value to 
intensity lookup table, also called a transfer function).

	RIFF (Raster Image File Format) is the native format for ImageStudio.
It can store grayscale information up to 256 grays per pixel, and can store
color information with a color lookup table (although I know of nothing that
will read a color RIFF file).

	Since ThunderScan and ImageStudio both run on Non-Mac-II's, GrayMap
and RIFF files are somewhat more universal than anything using a PICT format.
TIFF is quite universal (even when moving to IBM-PC's, although byte-ordering
may become a problem if the importing application isn't careful), but
can contain so many different kinds of information you never quite know
what you'll get.

Hope this helps.

-Eric
                      (defun maybe (x) (maybe (not x)))
Eric K. Olson     olson@endor.harvard.edu     harvard!endor!olson     D0760
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