term% cat index.txt PICOPEN(9.2) PICOPEN(9.2)
NAME
picopen_r, picopen_w, picread, picwrite, picclose, rdpicfile, wrpic‐
file, 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 writing. The name
"OUT" refers to standard output. Type is a TYPE attribute, as de‐
scribed 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 attri‐
bute; the length of this string becomes the value of NCHAN. Argv, if
nonzero, is conventionally the second argument of the main program; see
exec(2). It becomes a COMMAND attribute recording 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 con‐
ventional 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 com‐
putes 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 at‐
tributes, 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 separated 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 separate 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
standard machine-independent byte ordering.
EXAMPLES
Unpack the green and z channels from a file with channels rgbz...
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 trans‐
portable.
There is no code to support TYPE=ccir601 and the various ccitt fax com‐
pression types.
PICOPEN(9.2)