VXrbufimage, VXsbufimage − VisionX multiframe image access

int VXrbufimage(iset, vfile, n);
VisXimage_t *iset;
VisXfile_t *vfile;
int n;
VisXimage_t * VXsbufimage(vfile, n);
VisXfile_t *vfile;
int n;

Multiframe image files in VisionX consisted of a set of "frames" which are delimited by begin frame (VX_FRAME) and end frame (VX_EFRAME) elements and contain at least one image (see VXmakeimage(3)). An image consists of two consecutive data elements, a bounding box followed by a conforming pixel data element. VXsbufimage and VXrbufimage manage a set of n consecutive image frames in memory.

Spatiotemporal and other filtering operations often require that a number of image frames be accessible a the same time. VXsbufimage creates a buffer of n image structures (where n is a program specified constant) an reads the first (n-1) frames from the specified file. Note, each frame must contain at least one image. The image structure is initialized for the first image found in the frame (and the whole frame list is available as the .list element of the image structure). VXsbufimage returns a pointer to the image structure buffer that it creates.

VXrbufimage deletes the oldest frame in the image buffer, moves all remaining images to one later in the buffer and then reads the next image frame into the vacated first element of the image buffer. If VXrbufimage is unable to read another image frame it returns zero, otherwise it returns 1.

The usage of VXsbufimage and VXrbufimage are best illustrated by an example. Consider that we wish to perform an operation on a sequence of images that is a function of n consecutive image frames. This may be realized by the following program structure:

VisXimage_t *iset;
VisXfile_t *ifile, ofile;
int n;
         ifile = VXopen(<name>, 0);      /* open input file */
         ofile = VXopen(<name1>, 1);     /* open output file */

n = ...;

iset = VXsbufimage(vfile, n);

while (VXrbufimage(iset, vfile, n)){

/* process images iset[0] to iset[n-1] */

/* place the resulting image in iset[n-1] */

writeframe(ofile, iset[n-1].list);

}

Note: iset[0] contains the most recently read image, iset[n-1] contains the oldest image. The above program does not write out the first n-1 frames; therefore, the resulting image sequence will have n-1 fewer frames than the input file. The above is only one example of how to use these functions there are many other possibilities. The value of n must not be changed during the execution of the program.

VXmakeimage(3), VXfloatimage(3)

A. P. Reeves