3.1: threshold: EdgePlus

src/djvul.h

@@ -4,7 +4,7 @@
 
 #ifndef DJVUL_H_
 #define DJVUL_H_
-#define DJVUL_VERSION "3.0"
+#define DJVUL_VERSION "3.1"
 
 #include <stdbool.h>
 #include <math.h>
@@ -34,6 +34,7 @@ DJVULAPI int ImageDjvulSelect(unsigned char* buf, bool* bufmask, unsigned char*
 #define TBIMOD 1
 #define TSAUVOLA 2
 #define TBLUR 3
+#define TEDGEPLUS 4
 
 #ifdef DJVUL_IMPLEMENTATION
 
@@ -996,6 +997,10 @@ DJVULAPI int ImageDjvulSelect(unsigned char* buf, bool* bufmask, unsigned char*
         (void)ImageThresholdBlur(buf, bufmask, width, height, channels, radius, fbscale, delta, sensitivity);
         return ImageDjvulGround(buf, bufmask, bufbg, buffg, width, height, channels, bgs, level, doverlay);
         break;
+    case TEDGEPLUS:
+        (void)ImageThresholdEdgePlus(buf, bufmask, width, height, channels, radius, fbscale, delta, sensitivity);
+        return ImageDjvulGround(buf, bufmask, bufbg, buffg, width, height, channels, bgs, level, doverlay);
+        break;
     default:
         return ImageDjvulThreshold(buf, bufmask, bufbg, buffg, width, height, channels, bgs, level, wbmode, doverlay, anisotropic, contrast, fbscale, delta);
         break;

src/stbdjvul.c

@@ -24,7 +24,7 @@ void djvul_usage(char* prog, unsigned int bgs, unsigned int fgs, unsigned int le
     printf("  -o N.N    part of overlay blocks (default %f)\n", doverlay);
     printf("  -r        rewrite maks in ground mode\n");
     printf("  -s N.N    sensitivity Sauvola and Blur threshold (default %f)\n", sensitivity);
-    printf("  -t NUM    threshold: 0 - DjVuL, 1 - BiMod, 2 - Sauvola, 3 - Blur (default %d)\n", tmode);
+    printf("  -t NUM    threshold: 0 - DjVuL, 1 - BiMod, 2 - Sauvola, 3 - Blur, 4 - EdgePlus (default %d)\n", tmode);
     printf("  -w        white/black mode (default %d)\n", wbmode);
     printf("  -h        show this help message and exit\n");
 }
@@ -116,7 +116,7 @@ int main(int argc, char **argv)
             break;
         case 't':
             tmode = atoi(optarg);
-            if ((tmode < 0) || (tmode > 3))
+            if ((tmode < 0) || (tmode > 4))
             {
                 fprintf(stderr, "Bad argument\n");
                 fprintf(stderr, "threshold = %d\n", tmode);
@@ -376,6 +376,9 @@ int main(int argc, char **argv)
         case TBLUR:
             printf("threshold: Blur\n");
             break;
+        case TEDGEPLUS:
+            printf("threshold: EdgePlus\n");
+            break;
         default:
             printf("threshold: DjVuL\n");
             break;

src/threshold.h

@@ -4,7 +4,7 @@
 
 #ifndef THRESHOLD_H_
 #define THRESHOLD_H_
-#define THRESHOLD_VERSION "3.0"
+#define THRESHOLD_VERSION "3.1"
 
 #include <stdbool.h>
 #include <math.h>
@@ -23,6 +23,7 @@ THRESHOLDAPI int ImageThreshold(unsigned char* buf, bool* bufmask, unsigned int
 THRESHOLDAPI int ImageThresholdBimod(unsigned char* buf, bool* bufmask, unsigned int width, unsigned int height, unsigned int channels, float part, float delta);
 THRESHOLDAPI int ImageThresholdSauvola(unsigned char* buf, bool* bufmask, unsigned int width, unsigned int height, unsigned int channels, int radius, float sensitivity, float part, int lower_bound, int upper_bound, float delta);
 THRESHOLDAPI int ImageThresholdBlur(unsigned char* buf, bool* bufmask, unsigned int width, unsigned int height, unsigned int channels, float raduis, float part, float delta, float sensitivity);
+THRESHOLDAPI int ImageThresholdEdgePlus(unsigned char* buf, bool* bufmask, unsigned int width, unsigned int height, unsigned int channels, float raduis, float part, float delta, float sensitivity);
 
 #ifdef __cplusplus
 }
@@ -638,6 +639,64 @@ THRESHOLDAPI int ImageThresholdBlur(unsigned char* buf, bool* bufmask, unsigned
     return threshold;
 }
 
+/*
+ImageThresholdEdgePlus()
+
+input:
+buf - unsigned char* image (height * width * channels)
+part = 1.0f [1:1]
+delta = 0.0f [off, regulator]
+sensitivity = 0.2;
+
+output:
+bufmask - bool* image mask (height * width)
+threshold - threshold value
+
+Use:
+int threshold = ImageThresholdEdgePlus(buf, bufmask, width, height, channels, raduis, part, delta, sensitivity);
+*/
+
+THRESHOLDAPI int ImageThresholdEdgePlus(unsigned char* buf, bool* bufmask, unsigned int width, unsigned int height, unsigned int channels, float raduis, float part, float delta, float sensitivity)
+{
+    int threshold = 0;
+    unsigned int y, x, d;
+    float imo, imx, edge, edgeplus;
+    unsigned long int k;
+    unsigned char *bufb = NULL;
+
+    if ((bufb = (unsigned char*)malloc(height * width * channels * sizeof(unsigned char))))
+    {
+        ImageCopy(buf, bufb, width, height, channels);
+        (void)GaussBlurFilter(bufb, width, height, channels, raduis, raduis);
+        k = 0;
+        for (y = 0; y < height; y++)
+        {
+            for (x = 0; x < width; x++)
+            {
+                for (d = 0; d < channels; d++)
+                {
+                    imo = (float)buf[k];
+                    imx = (float)bufb[k];
+                    edge = (imo + 1.0f) / (imx + 1.0f) - 0.5f;
+                    edgeplus = imo * edge;
+                    imx = sensitivity * edgeplus + (1.0f - sensitivity) * imo;
+                    imx = (imx < 0.0f) ? 0.0f : (imx < 255.0f) ? imx : 255.0f;
+                    bufb[k] = (unsigned char)imx;
+                    k++;
+                }
+            }
+        }
+        threshold = ImageThresholdBimod(bufb, bufmask, width, height, channels, part, delta);
+        free(bufb);
+    }
+    else
+    {
+        threshold = ImageThresholdBimod(buf, bufmask, width, height, channels, part, delta);
+    }
+
+    return threshold;
+}
+
 #endif /* THRESHOLD_IMPLEMENTATION */
 
 #endif /* THRESHOLD_H_ */