Threshold an image to create a "binary" or "boolean" black and white image, in C with the VIPS library. Revised version of threshold1.c. Uses vips_image_new to create a dummy object. vips_object_local_array is used to create an array of VipsImage pointers - the array is hung off the dummy VipsObject, so everything gets cleaned up when the dummy …

threshold2.c

/** threshold2.c
 *
 * COMPILE
 *
 * gcc -Wall -o threshold2 threshold2.c `pkg-config vips --cflags --libs`
 *
 * EXAMPLE
 *
 * ./threshold2 128 in.png out.png 
 *
 */

#include <vips/vips.h>

int main (int argc, char** argv) {
    if (VIPS_INIT(argv[0]))
        vips_error_exit(NULL);
    
    if (argc != 4) {
        printf("USAGE: %s <THRESHOLD (0-255)> <INPUT_IMAGE_PATH> "
               "<OUTPUT_IMAGE_PATH>", argv[0]);
        vips_error_exit(NULL);
    }

    VipsObject* context = (VipsObject*) vips_image_new();
    VipsImage** t = (VipsImage**) vips_object_local_array(context, 4);

    double threshold = strtod(argv[1], NULL);

    if (!(t[0] = vips_image_new_from_file(argv[2],
            "access", VIPS_ACCESS_SEQUENTIAL, NULL)) ||
            vips_colourspace(t[0], &t[1], VIPS_INTERPRETATION_B_W, NULL) ||
            vips_extract_band(t[1], &t[2], 0, "n", 1, NULL) ||
            vips_moreeq_const1(t[2], &t[3], threshold, NULL) ||
            vips_image_write_to_file(t[3], argv[3], NULL)) {
        g_object_unref(context);
        vips_error_exit(NULL);
    }

    g_object_unref(context);

    return EXIT_SUCCESS;
}