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