Usage: autotrace [options] <input_file_name>
Options:<input_file_name> must be a supported image file.
  You can use '--' or '-' to start an option.
  You can use any unambiguous abbreviation for an option name.
  You can separate option names and values with '=' or ' '.

-background-color <hexadecimal>: the color of the background that should
    be ignored, for example FFFFFF; default is no background color.

-centerline: trace a character's centerline, rather than its outline.

-charcode <unsigned>: code of character to load from GF font file.

-color-count <unsigned>: number of colors a color bitmap is reduced to,
    it does not work on grayscale, allowed are 1..256;
    default is 0, that means no color reduction is done.

-corner-always-threshold <angle-in-degrees>: if the angle at a pixel is
    less than this, it is considered a corner, even if it is within
    `corner-surround' pixels of another corner; default is 60.

-corner-surround <unsigned>: number of pixels on either side of a
    point to consider when determining if that point is a corner;
    default is 4.

-corner-threshold <angle-in-degrees>: if a pixel, its predecessor(s),
    and its successor(s) meet at an angle smaller than this, it's a
    corner; default is 100.

-despeckle-level <unsigned>: 0..20; default is 0: no despeckling.

-despeckle-tightness <real>: 0.0..8.0; default is 2.0.

-dpi <unsigned>: The dots per inch value in the input image, affects scaling
    of mif output image


-error-threshold <real>: subdivide fitted curves that are off by
    more pixels than this; default is 2.0.

-filter-iterations <unsigned>: smooth the curve this many times
    before fitting; default is 4.

-input-format: Available formats: ppm, png, pbm, pnm, bmp, tga, pgm, gf.

-help: print this message.

-line-reversion-threshold <real>: if a spline is closer to a straight
    line than this, weighted by the square of the curve length, keep it a
    straight line even if it is a list with curves; default is .01.

-line-threshold <real>: if the spline is not more than this far away
    from the straight line defined by its endpoints,
    then output a straight line; default is 1.

-list-output-formats: print a list of supported output formats to stderr.

-list-input-formats: print a list of supported input formats to stderr.

-log: write detailed progress reports to <input_name>.log.

-noise-removal <real>:: 0.0..1.0; default is 0.99.

-output-file <filename>: write to <filename>

-output-format <format>: use format <format> for the output file. Available formats:
    rpl, tk, cfdg, xfig, plot, svg, plot-svg, gschem, gmfa, text, epd, tek, rib, sk, plot-tek, gmfb, pcl, txt, asy, plot-pcl, tex, gnuplot, cairo, dat, plot-hpgl, lwo, pcb, xml, dr2d, pov, dxf_14, eps, tfig, mp, meta, java1, hpgl, ai, cgm, pdf, latex2e, ps2ai, p2e, java2, pic, svm, plot-cgm, plot-ai, plt, noixml, vtk, tgif, idraw, fig, emf, plot-fig, kil, er, m, dxf, obj, ugs, pcbfill, mif, mma, java, gcode, c, dxf_s, ild, mpost, pcbi

-preserve-width: preserve line width prior to thinning.

-remove-adjacent-corners: remove corners that are adjacent.

-tangent-surround <unsigned>: number of points on either side of a
    point to consider when computing the tangent at that point; default is 3.

-report-progress: report tracing status in real time.

-debug-arch: print the type of cpu.

-debug-bitmap: dump loaded bitmap to <input_name>.bitmap.ppm or pgm.

-version: print the version number of this program.

-width-weight-factor <real>: weight factor for fitting the linewidth.


You can get the source code of autotrace from 
https://github.com/autotrace/autotrace

gcc sample.c `pkg-config --libs autotrace` `pkg-config --cflags autotrace`

/* sample.c */
#include <autotrace/autotrace.h>

int main()
{
  char * fname = "img/triangle.png";
  at_fitting_opts_type * opts = at_fitting_opts_new();
  at_input_read_func rfunc = at_input_get_handler(fname);
  at_bitmap_type * bitmap ;
  at_splines_type * splines;
  at_output_write_func wfunc = at_output_get_handler_by_suffix("eps");

  bitmap = at_bitmap_read(rfunc, fname, NULL, NULL, NULL);
  splines = at_splines_new(bitmap, opts, NULL, NULL);
  at_splines_write(wfunc, stdout, "", NULL, splines, NULL, NULL);
  return 0;
}