add lobal BW threshold on 8 bpp images

agl · Dec 23, 2024 · 528a5f4 · 528a5f4
1 parent 0625330
commit 528a5f4
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Showing 2 changed files with 38 additions and 14 deletions.
diff --git a/AUTHORS b/AUTHORS
@@ -4,6 +4,7 @@ Adam Langley <agl@imperialviolet.org>
 
 Contributors:
 =============
+Dan Bloomberg <dan.bloomberg@gmail.com>
 Misty De Meo <mistydemeo@gmail.com>
 zdenop <zdenop@gmail.com>
 Steven Lee http://www.rubypdf.com

diff --git a/src/jbig2.cc b/src/jbig2.cc
@@ -49,7 +49,8 @@
 #define JBIG2_WEIGHT_DEF 0.5f
 #define BW_THRESHOLD_MIN 0
 #define BW_THRESHOLD_MAX 255
-#define BW_THRESHOLD_DEF 128
+#define BW_LOCAL_THRESHOLD_DEF 200
+#define BW_GLOBAL_THRESHOLD_DEF 128
 
 static void
 usage(const char *argv0) {
@@ -61,7 +62,9 @@ usage(const char *argv0) {
   fprintf(stderr, "  -s --symbol-mode: use text region, not generic coder\n");
   fprintf(stderr, "  -t <threshold>: set classification threshold for symbol coder (def: %0.2f)\n", JBIG2_THRESHOLD_DEF);
   fprintf(stderr, "  -w <weight>: set classification weight for symbol coder (def: %0.2f)\n", JBIG2_WEIGHT_DEF);
-  fprintf(stderr, "  -T <bw threshold>: set 1 bpp threshold (def: %d)\n", BW_THRESHOLD_DEF);
+  fprintf(stderr, "  -T <bw threshold>: set 1 bpp threshold (def: %d)\n", BW_LOCAL_THRESHOLD_DEF);
+  fprintf(stderr, "  -G --global: use global BW threshold on 8 bpp images;\n"
+                  "               the default is to use local (adaptive) thresholding\n");
   fprintf(stderr, "  -r --refine: use refinement (requires -s: lossless)\n");
   fprintf(stderr, "  -O <outfile>: dump thresholded image as PNG\n");
   fprintf(stderr, "  -2: upsample 2x before thresholding\n");
@@ -213,13 +216,14 @@ int
 main(int argc, char **argv) {
   bool duplicate_line_removal = false;
   bool pdfmode = false;
+  bool globalmode = false;
+  int bw_threshold = BW_LOCAL_THRESHOLD_DEF;
   float threshold = JBIG2_THRESHOLD_DEF;
   float weight = JBIG2_WEIGHT_DEF;
-  int bw_threshold = BW_THRESHOLD_DEF;
   bool symbol_mode = false;
   bool refine = false;
   bool up2 = false, up4 = false;
-  const char *output_threshold = NULL;
+  const char *output_threshold_image = NULL;
   const char *basename = "output";
   l_int32 img_fmt = IFF_PNG;
   const char *img_ext = "png";
@@ -294,7 +298,7 @@ main(int argc, char **argv) {
     }
 
     if (strcmp(argv[i], "-O") == 0) {
-      output_threshold = argv[i+1];
+      output_threshold_image = argv[i+1];
       i++;
       continue;
     }
@@ -320,9 +324,11 @@ main(int argc, char **argv) {
         return 1;
       }
 
-      if ((threshold < JBIG2_THRESHOLD_MIN) || (threshold > JBIG2_THRESHOLD_MAX)) {
+      if ((threshold < JBIG2_THRESHOLD_MIN) ||
+          (threshold > JBIG2_THRESHOLD_MAX)) {
         fprintf(stderr, "Invalid value for threshold\n");
-        fprintf(stderr, "(must be between %0.2f and %0.2f)\n", JBIG2_THRESHOLD_MIN, JBIG2_THRESHOLD_MAX);
+        fprintf(stderr, "(must be between %0.2f and %0.2f)\n",
+                JBIG2_THRESHOLD_MIN, JBIG2_THRESHOLD_MAX);
         return 10;
       }
       i++;
@@ -340,13 +346,24 @@ main(int argc, char **argv) {
 
       if ((weight < JBIG2_WEIGHT_MIN) || (weight > JBIG2_WEIGHT_MAX)) {
         fprintf(stderr, "Invalid value for weight\n");
-        fprintf(stderr, "(must be between %0.2f and %0.2f)\n", JBIG2_WEIGHT_MIN, JBIG2_WEIGHT_MAX);
+        fprintf(stderr, "(must be between %0.2f and %0.2f)\n",
+                JBIG2_WEIGHT_MIN, JBIG2_WEIGHT_MAX);
         return 10;
       }
       i++;
       continue;
     }
 
+    // Local BW thresholding is the default.  However, if global
+    // BW thresholding is requested, use its default threshold.
+    if (strcmp(argv[i], "-G") == 0 ||
+        strcmp(argv[i], "--global") == 0) {
+      globalmode = true;
+      bw_threshold = BW_GLOBAL_THRESHOLD_DEF;
+      continue;
+    }
+
+    // If a BW threshold value is requested, overwrite the default value.
     if (strcmp(argv[i], "-T") == 0) {
       char *endptr;
       bw_threshold = strtol(argv[i+1], &endptr, 10);
@@ -356,7 +373,8 @@ main(int argc, char **argv) {
         return 1;
       }
       if (bw_threshold < BW_THRESHOLD_MIN || bw_threshold > BW_THRESHOLD_MAX) {
-        fprintf(stderr, "Invalid bw threshold: (%d..%d)\n", BW_THRESHOLD_MIN, BW_THRESHOLD_MAX);
+        fprintf(stderr, "Invalid bw threshold: (%d..%d)\n",
+                BW_THRESHOLD_MIN, BW_THRESHOLD_MAX);
         return 11;
       }
       i++;
@@ -418,7 +436,8 @@ main(int argc, char **argv) {
     return 6;
   }
 
-  struct jbig2ctx *ctx = jbig2_init(threshold, weight, 0, 0, !pdfmode, refine ? 10 : -1);
+  struct jbig2ctx *ctx = jbig2_init(threshold, weight, 0, 0,
+                         !pdfmode, refine ? 10 : -1);
   int pageno = -1;
 
   int numsubimages=0, subimage=0, num_pages = 0;
@@ -456,7 +475,7 @@ main(int argc, char **argv) {
     if (verbose)
       pixInfo(source, "source image:");
 
-    PIX *pixl, *gray, *pixt;
+    PIX *pixl, *gray, *adapt, *pixt;
     if ((pixl = pixRemoveColormap(source, REMOVE_CMAP_BASED_ON_SRC)) == NULL) {
       fprintf(stderr, "Failed to remove colormap from %s\n", argv[i]);
       return 1;
@@ -474,7 +493,11 @@ main(int argc, char **argv) {
         fprintf(stderr, "Unsupported input image depth: %d\n", pixl->d);
         return 1;
       }
-      Pix *adapt = pixBackgroundNormSimple(gray, NULL, NULL);
+      if (!globalmode) {
+        adapt = pixCleanBackgroundToWhite(gray, NULL, NULL, 1.0, 90, 190);
+      } else {
+        adapt = pixClone(gray);
+      }
       pixDestroy(&gray);
       if (up2) {
         pixt = pixScaleGray2xLIThresh(adapt, bw_threshold);
@@ -494,8 +517,8 @@ main(int argc, char **argv) {
     if (verbose)
       pixInfo(pixt, "thresholded image:");
 
-    if (output_threshold) {
-      pixWrite(output_threshold, pixt, IFF_PNG);
+    if (output_threshold_image) {
+      pixWrite(output_threshold_image, pixt, IFF_PNG);
     }
 
     if (segment && pixl->d > 1) {