TH PICOPEN 9.2
SH NAME
picopen_r, picopen_w, picread, picwrite, picclose, rdpicfile, wrpicfile, picputprop, picgetprop, picunpack, picpack \- picture file I/O
SH SYNOPSIS
B
#include <libg.h>
PP
B
#include <fb.h>
PP
B
PICFILE *picopen_r(char *name)
PP
B
PICFILE *picopen_w(char *name, char *type, int x0, int y0, int w, int h, char *chan, char *argv[], char *cmap)
PP
B
int picread(PICFILE *pf, char *buf)
PP
B
int picwrite(PICFILE *pf, char *buf)
PP
B
void picclose(PICFILE *pf)
PP
B
Bitmap *rdpicfile(PICFILE *pf, int ldepth)
PP
B
int wrpicfile(PICFILE *pf, Bitmap *b)
PP
B
PICFILE *picputprop(PICFILE *pf, char *name, char *value)
PP
B
char *picgetprop(PICFILE *pf, char *name)
PP
B
void picunpack(PICFILE *pf, char *pix, char *fmt, ...)
PP
B
void picpack(PICFILE *pf, char *pix, char *fmt, ...)
PP
SH DESCRIPTION
These functions read and write raster images in
IR picfile (9.6)
format.
Open picture files are referred to by pointers of type
BR PICFILE* .
PP
I Picopen_r
opens the named picfile for reading and returns a pointer
to the open file.
If
I name
is
L
"IN"\fR,
standard input is used.
PP
I Picopen_w
similarly creates the named image file for writing.
The name
L
"OUT"
refers to standard output.
I Type
is a
B TYPE
attribute, as described in
IR picfile (9.6);
I x0
and
I y0
are the upper left coordinates of the
BR WINDOW
attribute;
I w
and
I h
are the image width and height in pixels.
I Chan
is a string specifying the order of channels for the
B CHAN
attribute; the length of this string becomes the value of
BR NCHAN .
IR Argv ,
if nonzero, is
conventionally the second argument of the main program;
see
IR exec (2).
It becomes a
B COMMAND
attribute recording the provenance of the file.
PP
The special call
B picopen_w(\c
IB name ,
BI PIC_SAMEARGS( pf ))
creates a file with the same attributes as an already open
picfile.
B PIC_SAMEARGS
mentions
I argv
by name, hence the name must be in scope at the point of call.
PP
I Picread
and
I picwrite
read or write a single row of pixels using the
character array
IR buf .
The length of the row is determined from the file's
B WINDOW
and
B NCHAN
attributes.
One-bit-per-pixel images (of type
B bitmap
or
BR ccitt-g4 ,
for example)
are decoded to one byte per pixel, 0 for black, 255 for white, and
are encoded as 1 for pixel values less than 128 and 0 otherwise.
Files of type
B ccir601
are decoded into conventional
B rgb
channels.
PP
I Picclose
closes a picture file and frees associated storage.
PP
I Wrpicfile
copies a bitmap into a picture file.
I Rdpicfile
allocates a
B Bitmap
of given
I ldepth
and reads picture file into it.  Since
B Bitmaps
are usually monochrome and only one or two bits deep,
I rdpicfile
computes the NTSC luminance of the input image and
uses Floyd-Steinberg error-diffusion dither to hide
quantization errors.
PP
I Picputprop
called after
I picopen_w
but before
I picwrite
adds header attributes, returning the revised
B PICFILE
pointer.
PP
I Picgetprop
returns a pointer to the value of the named attribute, or
0 if the picfile does not have the attribute.
In both
I Picputprop
and
IR picgetprop ,
with multiple appearances (e.g.
BR COMMAND )
are expressed as a sequence of
values separated by newlines.
PP
The header file defines macros to extract commonly-used
attributes:
IP
EX
PIC_NCHAN(pf), PIC_WIDTH(pf), PIC_HEIGHT(pf),
PIC_SAMEARGS(pf) \fR(see \fP\&picopen_w\fR)\fP
EE
PP
I Picunpack
extracts the channels of pixel array
I pix
into separate array
I args
of types described by the
I fmt
character string.
Format characters are
BR c ,
BR s ,
BR l ,
BR f ,
BR d ,
for arrays of types unsigned char, short, long,
float, and double.
Format character
B _
designates a picfile channel to be skipped.
I Picpack
reverses the process.
These routines effect a standard machine-independent byte
ordering.
SH EXAMPLES
Unpack the green and z channels from a file with channels
B rgbz...
br
ns
IP
EX
PICFILE *pf = picopen_r("file");
extern char pixels[], green[][1000];
extern float zdepth[][1000];
for(i=0; picread(pf, pixels); i)
       picunpack(pf, pixels, "_c_f", green[i], zdepth[i]);
EE
PP
Reflect a picture about its vertical midline.
br
ns
IP
EX
PICFILE *in = picopen_r("picture");
PICFILE *out = picopen_w("OUT", PIC_SAMEARGS(in));
int w = PIC_WIDTH(in);
int n = PIC_NCHAN(in);
char *buffer = malloc(w*n), *temp = malloc(n);
while (picread(in, buffer)) {
       char *left = buffer;
       char *right = buffer + n*(w - 1);
       for( ; left<right; left+=n, right-=n) {
               memmove(temp, left, n);
               memmove(left, right, n);
               memmove(right, temp, n);
       }
       picwrite(out, buffer);
}
EE
SH SOURCE
B /sys/src/libfb
SH SEE ALSO
IR picfile (9.6)
SH DIAGNOSTICS
I Picread
returns 1 on success, 0 on end of file or error.
br
I Picopen_r
and
I picopen_w
return 0 for unopenable files.
All three set
IR errstr (2)
to explain their failure.
SH BUGS
I Picpack
and
I picunpack
store and retrieve floating point channels (types
B f
and
BR d )
using native floating-point, rather than something
transportable.
PP
There is no code to support
B TYPE=ccir601
and the various
B ccitt
fax compression types.

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