ref: 82a3f55c5fb7b9f7a82449e4eb943c535ec3e491
dir: /man/2/imagefile/
.TH IMAGEFILE 2
.SH NAME
imagefile: readgif, readjpg, readpicfile, readpng, readxbitmap, remap \- processing external image file formats
.SH SYNOPSIS
.EX
include "imagefile.m";
gifreader := load RImagefile RImagefile->READGIFPATH;
jpgreader := load RImagefile RImagefile->READJPGPATH;
xbmreader := load RImagefile RImagefile->READXBMPATH;
picreader := load RImagefile RImagefile->READPICPATH;
pngreader := load RImagefile RImagefile->READPNGPATH;
imageremap := load Imageremap Imageremap->PATH;
Rawimage: adt
{
r: Draw->Rect;
cmap: array of byte;
nchans: int;
chans: array of array of byte;
chandesc: int;
init: fn(bufio: Bufio);
read: fn(fd: ref Bufio->Iobuf): (ref Rawimage, string);
readmulti: fn(fd: ref Bufio->Iobuf):
(array of ref Rawimage, string);
};
init: fn(bufio: Bufio);
writeimage: fn(fd: ref Bufio->Iobuf, image: ref Draw->Image)
: string;
remap: fn(i: ref RImagefile->Rawimage, d: ref Draw->Display,
errdiff: int): (ref Draw->Image, string);
.EE
.SH DESCRIPTION
The
.B Rawimage
.B adt
of module
.B RImagefile
defines an internal representation
and routines for reading images such as GIF and JPEG files.
To read a set of files of a given format, load the appropriate module,
pass its
.B init
function an implementation of the
.B Bufio
module, and pass
.B read
an
.B Bufio->Iobuf
for each file.
.B Read
returns a tuple: a
.B ref
.B Rawimage
that holds the image and an error string.
If the
.B Rawimage
is
.BR nil ,
the error string will report the reason.
Files (particularly GIF files) are often incorrectly encoded but yield usable pictures,
so even if a
.B Rawimage
is returned, the error string may still report problems.
.PP
Some image file types (eg, GIF) support having several images in a single file.
They can be read in all at once using
.BR readmulti ,
which returns a tuple with the array of images, and an error string as above.
.PP
The
.B Rawimage
is always defined as one or more bytes per pixel, with
.B nchans
channels of data stored in the array
.BR chans .
The
.B chandesc
field, described below, specifies the contents of
.BR chans .
The
rectangle
.B r
describes the shape of the picture.
.PP
The
.B Rawimage
type can be converted to a regular
.B Image
(see
.IR draw-image (2))
by calling module
.BR Imageremap 's
function
.B remap.
.B Remap
is passed the
.BR Rawimage ,
a
.B Display
on which to create the image, and a flag that specifies whether to apply Floyd-Steinberg
error diffusion code to the result, for smoother rendering of colours at the cost of
some noise in the image.
.PP
How to remap is defined by the
.B RImagefile
itself: the field
.B chandesc
specifies the type of the various
.B chans
of data:
.B RImagefile->CRGB
specifies a 3-colour RGB image with no colour map;
.B RImagefile->CY
a monotone (luminance-only, grey-scale) image with no colour map;
and
.B RImagefile->CRGB1
a single-channel image with RGB colour map in
.BR cmap .
The file readers set
.B chandesc
as appropriate for the format of the file.
.PP
The writing of image files is defined by the module
.BR WImagefile.
To initialize the module, call its
.B init
function with an instance of the
.B Bufio
module and pass its
.B writeimage
function a
.B Bufio->Iobuf
representing the output stream and an image of type
.B Draw->Image.
.PP
These functions are split into separate modules to give applications control over
the memory they need to process images.
.SH SOURCE
.B /appl/lib/readgif.b
.br
.B /appl/lib/readjpg.b
.br
.B /appl/lib/readxbitmap.b
.br
.B /appl/lib/readpicfile.b
.br
.B /appl/lib/readpng.b
.SH NOTES
The JPEG reader handles only the Baseline sequential format as defined by
the JFIF 1.02 file exchange format.
.PP
Functions to write these formats are as yet unimplemented.