miff
NAME
MIFF - Magick Image File Format is a platform-independent
format for storing bitmap images. MIFF is a part of the
ImageMagick toolkit of image manipulation utilities for the
X Window System. ImageMagick is capable of converting many
different image file formats to and from MIFF (e.g. JPEG,
XPM, TIFF, etc.).
SYNOPSIS
#include <image.h>
DESCRIPTION
A MIFF image file consist of two sections. The first
section is a header composed of keywords describing the
image in text form. The next section is the binary image
data. The header is separated from the image databy a :
character immediately followed by a newline.
The MIFF header is composed entirely of ASCII characters.
The fields in the header are keyword and value combination
in the keyword=value format, with each keyword and value
separated by an equal sign (=). Each keyword=value
combination is delimited by at least one control or
whitespace character. Comments may appear in the header
section and are always delimited by braces. The MIFF header
always ends with a colon (:) character, followed by a
newline character. It is also common for a formfeed and a
newline character to appear before the colon. You can then
list the image keywords with more(1), without printing the
binary image that follows the colon separator.
The following is a list of keyword=value combinations that
may be found in a MIFF file:
class=DirectClass
class=PseudoClass indicates the type of binary image
data stored in the MIFF file. If this keyword is not
present, DirectClass image data is assumed.
colors=value
specifies the number of colors in a DirectClass image.
For a PseudoClass image, this keyword specifies the
size of the colormap. If this keyword is not present
in the header, and the image is PseudoClass, a linear
256 color grayscale colormap is used with the image
data.
columns=value
indicates the width of the image in pixels. This is a
required keyword and has no default.
compression=RunlengthEncoded
compression=QEncoded indicates the type of algorithm
used to compress the image data. If this keyword is
not present, the image data is assumed to be
uncompressed.
id=ImageMagick
The id keyword identifies the file as a MIFF-format
image file. This keyword is required and has no
default. Although this keyword can appear anywhere in
the header, it should start as the first keyword of the
header in column 1. This will allow programs like
file(1) to easily identify the file as MIFF.
matte=True
matte=False specifies whether a DirectClass image has
matte data. Matte data is generally useful for image
compositing. This keyword has no meaning for pseudo-
color images.
montage=<width>x<height>{+-}<x offset>{+-}<y offset>
size and location of the individual tiles of a
composite image. See X(1) for details about the
geometry specification.
Use this keyword when the image is a composite of a number
of different tiles. A tile consists of an image and
optionally a border and a label. <width> is the size in
pixels of each individual tile in the horizontal direction
and <height> is the size in the vertical direction. Each
tile must have an equal number of pixels in width and equal
in height. However, the width can differ from the height.
<x offset> is the offset in number of pixels from the
vertical edge of the composite image where the first tile of
a row begins and <y offset> is the offset from the
horizontal edge where the first tile of a column begins.
If this keyword is specified, a directory of tile names must
follow the image header. The format of the directory is
explained below.
packets=value
specifies the number of compressed color packets in the
image data section. This keyword is optional for
RunlengthEncoded images, mandatory for QEncoded images,
and not used for uncompressed image.
rows=value
indicates the height of the image in pixels. This is a
required keyword and has no default.
scene=value
indicates the sequence number for this MIFF image file.
This optional keyword is used when a MIFF image file is
one in a sequence of files used in an animation.
signature=value
this optional keyword contains a string that uniquely
identifies the image colormap. Unique colormap
identifiers are normally used when animating a sequence
of PseudoClass images.
The following is a sample MIFF header. In this example,
<FF> is a formfeed character:
id=ImageMagick
class=PseudoClass colors=256
signature=d79e1c308aa5bbcdeea8ed63df412da9
compression=RunlengthEncoded packets=27601
columns=1280 rows=1024
scene=1
{
Rendered via Dore by Sandi Tennyson.
}
<FF>
:
Note that keyword=value combinations may be separated by
newlines or spaces and may occur in any order within the
header. Comments (within braces) may appear anywhere before
the colon.
If you specify the montage keyword in the header, follow the
header with a directory of image tiles. This directory
consists of a name for each tile of the composite image
separated by a newline character. The list is terminated
with a NULL character.
Following the header (or image directory if the montage
keyword is in the header) is the binary image data itself.
How the image data is formatted depends upon the class of
the image as specified (or not specified) by the value of
the class keyword in the header.
DirectClass images (class=DirectClass) are continuous-tone,
RGB images stored as intensity values in red-green-blue
order. Each color value is one byte in size [0..255] and
there are three bytes per pixel (four with an optional matte
value). The total number of pixels in a DirectClass image
is calculates by multiplying the rows value by the column
value in the header.
PseudoClass images (class=PseudoClass) are colormapped RGB
images. The colormap is stored as a series of red-green-
blue pixel values, each value being a byte in size. The
number of colormap entries is indicated by the colors
keyword in the header, with a maximum of 65,535 total
entries allowed. The colormap data occurs immediately
following the header (or image directory if the montage
keyword is in the header).
PseudoClass image data is an array of index values into the
color map. If these are 256 or fewer colors in the image,
each byte of image data contains an index value. If the
image contains more than 256 colors, then the index value is
stored as two contiguous bytes with the most significant
byte being first. The total number of pixels in a
PseudoClass image is calculated by multiplying the rows
value by the columns value in the header.
MIFF is capable of storing a digital signature for
colormapped images. This signature was developed for use
when animating a sequence of images on a colormapped X
server. All of the signatures in a sequence of MIFF files
are checked, and if they all match, you do not need to
compute a global colormap.
The default colormap identifier is a digital signature
computed using RSA's Data Security MD5 Digest Algorithm.
(See a description of this algorithm in Internet draft,
[MD5], July 1992. The colormap signature is computed if the
MIFF file is part of a scene (i.e. the scene value does not
equal 0).
The image data in a MIFF file may be uncompressed or may be
compressed using one of two algorithms. The compression
keyword in the header indicates how the image data is
compressed. The run-length encoding (RLE) algorithm may be
used to encode image data into packets of compressed data.
For DirectClass images, runs of identical pixels values (not
BYTE values) are encoded into a series of four-byte packets
(five bytes if a matte value is included). The first three
bytes of the packet contain the red, green, and blue values
of the pixel in the run. The fourth byte contains the
number of pixels in the run. This value is in the range of
0 to 255 and is one less than the actual number of pixels in
the run. For example, a value of 127 indicates that there
are 128 pixels in the run.
For PseudoClass images, the same RLE algorithm is used.
Runs of identical index values are encoded into packets.
Each packet contains the colormap index value followed by
the number of index values in the run. The number of bytes
n a PseudoClass RLE packet will be either two or three,
depending upon the size of the index values. The number of
RLE packets stored in the file is specified by the packets
keyword in the header, but is not required.
A more complex algorithm, the predictive arithmetic
compression algorithm found in the lossless JPEG compression
scheme, may be used to to achieve a greater compression
ratio than run-length encoding. PseudoClass images are
first promoted to DirectClass before encoding. The number
of compressed packets stored in the file is specified by the
packets keyword in the header.
MIFF files may contain more than one image. Simply
concatenate each individual image (composed of a header and
image data) into one file.
SEE ALSO
display(1), animate(1), import(1), montage(1), mogrify(1),
convert(1), more(1), compress(1)
COPYRIGHT
Copyright 1995 E. I. du Pont de Nemours and Company
Permission to use, copy, modify, distribute, and sell this
software and its documentation for any purpose is hereby
granted without fee, provided that the above copyright
notice appear in all copies and that both that copyright
notice and this permission notice appear in supporting
documentation, and that the name of E. I. du Pont de Nemours
and Company not be used in advertising or publicity
pertaining to distribution of the software without specific,
written prior permission. E. I. du Pont de Nemours and
Company makes no representations about the suitability of
this software for any purpose. It is provided "as is"
without express or implied warranty.
E. I. du Pont de Nemours and Company disclaims all
warranties with regard TO this software, including all
implied warranties of merchantability and fitness, in no
event shall E. I. du Pont de Nemours and Company be liable
for any special, indirect or consequential damages or any
damages whatsoever resulting from loss of use, data or
profits, whether in an action of contract, negligence or
other tortuous action, arising out of or in connection with
the use or performance of this software.
AUTHORS
John Cristy, E.I. du Pont de Nemours and Company
Incorporated