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 writing. 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 program; see exec(2). It becomes a COMMAND attribute recording the provenance of the file.

The special call picopen_w(.IB 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 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 transportable.

There is no code to support TYPE=ccir601 and the various ccitt fax compression types.