IMAGEFILE(2) IMAGEFILE(2)
NAME
imagefile: readgif, readjpg, readpicfile, readpng,
readxbitmap, remap - processing external image file formats
SYNOPSIS
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);
DESCRIPTION
The Rawimage adt of module 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 init function an
implementation of the Bufio module, and pass read an
Bufio->Iobuf for each file. Read returns a tuple: a ref
Rawimage that holds the image and an error string. If the
Rawimage is nil, the error string will report the reason.
Files (particularly GIF files) are often incorrectly encoded
but yield usable pictures, so even if a Rawimage is
returned, the error string may still report problems.
Some image file types (eg, GIF) support having several
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IMAGEFILE(2) IMAGEFILE(2)
images in a single file. They can be read in all at once
using readmulti, which returns a tuple with the array of
images, and an error string as above.
The Rawimage is always defined as one or more bytes per
pixel, with nchans channels of data stored in the array
chans. The chandesc field, described below, specifies the
contents of chans. The rectangle r describes the shape of
the picture.
The Rawimage type can be converted to a regular Image (see
draw-image(2)) by calling module Imageremap's function
remap. Remap is passed the Rawimage, a 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.
How to remap is defined by the RImagefile itself: the field
chandesc specifies the type of the various chans of data:
RImagefile->CRGB specifies a 3-colour RGB image with no
colour map; RImagefile->CY a monotone (luminance-only,
grey-scale) image with no colour map; and RImagefile->CRGB1
a single-channel image with RGB colour map in cmap. The
file readers set chandesc as appropriate for the format of
the file.
The writing of image files is defined by the module
WImagefile. To initialize the module, call its init func-
tion with an instance of the Bufio module and pass its
writeimage function a Bufio->Iobuf representing the output
stream and an image of type Draw->Image.
These functions are split into separate modules to give
applications control over the memory they need to process
images.
SOURCE
/appl/lib/readgif.b
/appl/lib/readjpg.b
/appl/lib/readxbitmap.b
/appl/lib/readpicfile.b
/appl/lib/readpng.b
NOTES
The JPEG reader handles only the Baseline sequential format
as defined by the JFIF 1.02 file exchange format.
Functions to write these formats are as yet unimplemented.
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