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 representa‐
tion 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 Rawim‐
age 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 images in a sin‐
gle 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 spec‐
ifies a 3-colour RGB image with no colour map; RImagefile->CY a mono‐
tone (luminance-only, grey-scale) image with no colour map; and RImage‐
file->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 function with an instance of the
Bufio module and pass its writeimage function a Bufio->Iobuf represent‐
ing 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.
IMAGEFILE(2)
