Add soble edge detection

C/src/ascii.c

@@ -1,5 +1,6 @@
 #include "ascii.h"
 
+#include <math.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -50,6 +51,31 @@ size_t ascii_out_size(int dst_w, int dst_h, int color) {
   }
 }
 
+// Sobel edge detection (kernel convolution)
+static void sobel(const uint8_t *in, uint8_t *out, int w, int h) {
+  static const int Gx[3][3] = {{-1, 0, 1}, {-2, 0, -2}, {-1, 0, 1}};
+  static const int Gy[3][3] = {{-1, -2, -1}, {0, 0, 0}, {1, 2, 1}};
+
+  for (int y = 1; y < h - 1; y++) {
+    for (int x = 1; x < w - 1; x++) {
+      int gx = 0, gy = 0;
+      for (int ky = -1; ky <= 1; ky++) {
+        for (int kx = -1; kx <= 1; kx++) {
+          int p = in[(y + ky) * w + (x + kx)];
+          gx += Gx[ky + 1][kx + 1] * p;
+          gy += Gy[ky + 1][kx + 1] * p;
+        }
+      }
+
+      // TEST: test both L1 and L2 normalisations
+      int mag = abs(gx) + abs(gy); // L1 normalisation
+      // int mag = sqrt(gx * gx + gy * gy); // L2 normalisation
+
+      out[y * w + x] = (uint8_t)(mag > 255 ? 255 : mag);
+    }
+  }
+}
+
 //  Grayscale to ascii
 int grayscale_to_ascii(const uint8_t *gray, const uint8_t *rgb, int src_w,
                        int src_h, int dst_w, int dst_h, char *out,
@@ -61,6 +87,7 @@ int grayscale_to_ascii(const uint8_t *gray, const uint8_t *rgb, int src_w,
   int contrast = opts ? opts->contrast : 100;
   int invert = opts ? opts->invert : 0;
   int do_color = opts && opts->color && (rgb != NULL);
+  int do_edges = opts ? opts->edges : 0;
   int do_dither = opts ? opts->dither : 0;
 
   // Blocking Widht and height pixels in source pixels
@@ -123,6 +150,18 @@ int grayscale_to_ascii(const uint8_t *gray, const uint8_t *rgb, int src_w,
     }
   }
 
+  // Sobel edge detection
+  if (do_edges) {
+    // Temporary  buffer for detected edges results
+    uint8_t *edge_buf = calloc(dst_w * dst_h, sizeof(uint8_t));
+    if (edge_buf) {
+      sobel(small_g, edge_buf, dst_w, dst_h);
+      // overwite grayscale image with edge map
+      memcpy(small_g, edge_buf, dst_w * dst_h);
+      free(edge_buf);
+    }
+  }
+
   // Floyd-Steinberg dithering
   if (do_dither) {
     int16_t *eb = malloc(dst_w * dst_h * sizeof(int16_t));

C/src/main.c

@@ -1,18 +1,18 @@
 #include "ascii.h"
 #include "capture.h"
-#include "timing.h"
 #include "thread_sharing.h"
+#include "timing.h"
 
 #include <getopt.h>
+#include <pthread.h>
 #include <signal.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <termios.h>
 #include <time.h>
 #include <unistd.h>
-#include <pthread.h>
-#include <stdint.h>
 
 // Defaults
 #define DEFAULT_ASCII_WIDTH 80
@@ -51,6 +51,7 @@ static void print_usage(const char *prog) {
       "  -b <val>      brightness offset        -128..128  (default: 0)\n"
       "  -c <val>      contrast in percent      >0; 100=none (default: 100)\n"
       "  -i            invert brightness->charset mapping\n"
+      "  -e            enable Sobel edge detection\n"
       "  -C            colour output (ANSI truecolor)\n"
       "  -D            Floyd-Steinberg dithering\n",
       prog, DEFAULT_CAPTURE_WIDTH, DEFAULT_CAPTURE_HEIGHT, DEFAULT_FPS,
@@ -62,7 +63,7 @@ void term_raw_mode(void) {
   tcgetattr(STDOUT_FILENO, &orig_terminal);
   struct termios raw = orig_terminal;
   raw.c_lflag &= ~(ICANON | ECHO); // no line buffering or no echo
-  raw.c_cc[VMIN] = 0;             // non-blocking read
+  raw.c_cc[VMIN] = 0;              // non-blocking read
   raw.c_cc[VTIME] = 0;
   tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw);
 }
@@ -87,13 +88,14 @@ int main(int argc, char *argv[]) {
       .contrast = 100,
       .invert = 0,
       .color = 0,
+      .edges = 0,
       .dither = 0,
       .charset = NULL,
   };
 
   // CLI parsing
   int opt;
-  while ((opt = getopt(argc, argv, "d:W:H:w:h:f:b:c:iCDs:")) != -1) {
+  while ((opt = getopt(argc, argv, "ed:W:H:w:h:f:b:c:iCDs:")) != -1) {
     switch (opt) {
     case 'd':
       device = optarg;
@@ -137,6 +139,9 @@ int main(int argc, char *argv[]) {
     case 'C':
       opts.color = 1;
       break;
+    case 'e':
+      opts.edges = 1;
+      break;
     case 'D':
       opts.dither = 1;
       break;
@@ -159,8 +164,8 @@ int main(int argc, char *argv[]) {
   }
   fprintf(stderr, "Device: %s | capture %dx%d | ASCII %dx%d | %d fps%s%s%s\n",
           device, cam.width, cam.height, ascii_w, ascii_h, fps,
-          opts.color ? " | color" : "", opts.dither ? " | dither" : "",
-          opts.invert ? " | inverted" : "");
+          opts.color ? " | color" : "", opts.edges ? " | edges" : "",
+          opts.dither ? " | dither" : "", opts.invert ? " | inverted" : "");
 
   // Allocate pixel buffers
   int cam_pixels = cam.width * cam.height;