Basic 2D Example Program

This is the standard template for implemetning algorithms that operation on conventional 2D images. This program allows the image file names to be specified on the command line, allows the threshold to be specified on the command line, and also works on image files that contain more than one image.

See the concept tutorial for a desction of the v4 image structures.


#include "VisXV4.h"    /* VisionX structure include file       */
#include "Vutil.h"     /* VisionX utility header files         */

VXparam_t par[] =      /* command line structure               */
{    "if=",    0, " input file  vthresh: threshold images"},
{    "of=",    0, " output file "},
{    "th=",    0, " Threshold value (default 50)"},
{     0,       0,    0}
#define  INIMAGE   par[0].val
#define  OUTIMAGE  par[1].val
#define  THRESHOLD par[2].val

int main(int argc, char** argv)
Vfstruct (im);
int x, y;
int thresh;

VXparse(&argc, &argv, par);  /* parse the command line         */
 if (THRESHOLD ) {
    thresh = atoi (THRESHOLD); 
 } else {
    thresh = 50;

 while ( Vfread( &im, INIMAGE) ) {
    if ( im.type != VX_PBYTE ) {
           fprintf (stderr, "error: image not byte type\n");
           exit (1);
    for ( y = im.ylo; y <= im.yhi; y++) {
       for ( x = im.xlo; x <= im.xhi; x++) {
          im.u[y][x] = im.u[y][x] >= thresh ? 255 : 0;
    Vfwrite( &im, OUTIMAGE);

  1. Command line parameters have now been added to this program.
  2. To perform exactly the same function as the previous program one would need to give the command:
    vthresh if=infile.vx of=outfile.vx
    The “par” structure defines a total of three parameters if= for the input file name and of= for the output file name; the if= and of= prefixes are used by convention throughout the VisionX system. A third optional parameter th= is also specified which allows the image threshold to be set to any value (not just 50).
  3. The VXparse function matches command line parameters where possible to the .val elements. Therefore, after parsing the command line specified above, the par .val elements would have the following contents:
    par[0].val   “inimage.vx”
    par[1].val    “outimage.vx
    par[2].val   “” 
    The #define statements in the program provide a convenient way to name the different par .val elements.
  4. If the th= option is specified on the command line then the string given as the threshold will be converted to an integer value by the atoi function and assigned to thresh.
  5. The program as written will correctly operate on images with any dimensions and any number of channels but will only operate on images of type unsigned byte. Therefore a check has been added to ensure that the input image file is of the correct type.
  6. Since there are no dependencies in this simple program there is no real need to create an image structure for the result; it may be written back into the original image. Also a more succinct c language version or the if expression in the first program is used in the second program which performs the same function.
Table 1 base pixel types supported by VisionX and their Vfstruct names
Vfstruct type Name C-Type Vfstruct Member Description
VX_PBYTE unsigned char .u most usual
byte format
VX_PFLOAT float .f 32-bit floating point
VX_PDOUBLE double .d 64-bit floating point
VX_PBIT unsigned char .b 1-bit (packed 8/byte)
VX_PCHAR char .c 8-bit signed integer
VX_PSHORT short .s 16-bit signed integer
VX_PINT int .i 32-bit signed integer
VX_PIDX unsigned char .u 8-bit color index