1.2025.12.21: threshold: add LCaM method

Author: zvezdochiot

src/imageproc/Binarize.cpp

@@ -874,6 +874,31 @@ BinaryImage binarizeLAAB(
     return bw_img;
 }  // binarizeLAAB
 
+/*
+ * LCaM = k * [mean + contrast * (256 - origin + delta) / 256], k = 0.75, delta = 0
+ *      contrast = Imax - Imin
+ *      mean = integral(I,w) / w
+ *      w = (2 * radius + 1) * (2 * radius + 1), radius = 5
+*/
+BinaryImage binarizeLCaM(
+    GrayImage const& src,
+    int const radius,
+    float const k,
+    int const delta,
+    unsigned char const bound_lower,
+    unsigned char const bound_upper)
+{
+    if (src.isNull())
+    {
+        return BinaryImage();
+    }
+
+    GrayImage threshold_map(grayLCaMMap(src, radius, k, delta));
+    BinaryImage bw_img(binarizeFromMap(src, threshold_map, 0, bound_lower, bound_upper));
+
+    return bw_img;
+}
+
 /*
  * WAN = (mean + max) / 2 * (1.0 + k * (stderr / 128.0 - 1.0)), k = 0.30
  * modification by zvezdochiot:

src/imageproc/Binarize.h

@@ -275,6 +275,22 @@ IMAGEPROC_EXPORT BinaryImage binarizeLAAB(
     unsigned char lower_bound = 0,
     unsigned char upper_bound = 255);
 
+/**
+ * \brief Image binarization using Local Contrast and Mean based Thresholding Technique in Image Binarization.
+ *
+ * O. Imocha Singh, Tejmani Sinam, O. James, T.Romen Singh
+ * International Journal of Computer Applications (0975 – 8887)
+ * Volume 51– No.6, August 2012
+ * https://research.ijcaonline.org/volume51/number6/pxc3881362.pdf
+ */
+IMAGEPROC_EXPORT BinaryImage binarizeLCaM(
+    GrayImage const& src,
+    int radius = 5,
+    float k = 0.75f,
+    int delta = 0,
+    unsigned char lower_bound = 0,
+    unsigned char upper_bound = 255);
+
 /**
  * \brief Image binarization using Fox adaptive thresholding method.
  *

src/imageproc/GrayImage.cpp

@@ -974,6 +974,67 @@ GrayImage grayWindowMap(
     return gmean;
 }  // grayWindowMap
 
+/*
+ * LCaM = k * [mean + contrast * (256 - origin + delta) / 256], k = 0.75, delta = 0
+ *      contrast = Imax - Imin
+ *      mean = integral(I,w) / w
+ *      w = (2 * radius + 1) * (2 * radius + 1), radius = 5
+*/
+GrayImage grayLCaMMap(
+    GrayImage const& src,
+    int const radius,
+    float const k,
+    int const delta)
+{
+    if (src.isNull())
+    {
+        return GrayImage();
+    }
+    GrayImage gmean = grayMapMean(src, radius);
+    if (gmean.isNull())
+    {
+        return GrayImage(src);
+    }
+
+    if (radius > 0)
+    {
+        GrayImage gcontrast = grayMapContrast(src, radius);
+        if (gcontrast.isNull())
+        {
+            return gmean;
+        }
+
+        int const w = src.width();
+        int const h = src.height();
+        unsigned char const* src_line = src.data();
+        int const src_stride = src.stride();
+        unsigned char* gmean_line = gmean.data();
+        int const gmean_stride = gmean.stride();
+        unsigned char* gcontrast_line = gcontrast.data();
+        int const gcontrast_stride = gcontrast.stride();
+
+        for (int y = 0; y < h; y++)
+        {
+            for (int x = 0; x < w; x++)
+            {
+                float const origin = src_line[x];
+                float const mean = gmean_line[x];
+                float const contrast = gcontrast_line[x];
+
+                float threshold = k * (mean + contrast * (256.0f - origin + delta) / 256.0f);
+
+                threshold = (threshold < 0.0f) ? 0.0f : ((threshold < 255.0f) ? threshold : 255.0f);
+                gmean_line[x] = (unsigned char) threshold;
+            }
+            src_line += src_stride;
+            gmean_line += gmean_stride;
+            gcontrast_line += gcontrast_stride;
+        }
+    }
+
+    return gmean;
+}  // grayLCaMMap
+
 /*
  * bradley = mean * (1.0 - k), k = 0.2
  */

src/imageproc/GrayImage.h

@@ -206,6 +206,11 @@ IMAGEPROC_EXPORT GrayImage grayWindowMap(
     int radius = 50,
     float k = 1.0f,
     int delta = 0);
+IMAGEPROC_EXPORT GrayImage grayLCaMMap(
+    GrayImage const& src,
+    int radius = 5,
+    float k = 0.75f,
+    int delta = 0);
 IMAGEPROC_EXPORT GrayImage grayBradleyMap(
     GrayImage const& src,
     int radius = 100,

src/stages/output/BlackWhiteOptions.cpp

@@ -236,6 +236,10 @@ BlackWhiteOptions::parseThresholdMethod(QString const& str)
     {
         return T_LAAB;
     }
+    else if (str == "lcam")
+    {
+        return T_LCAM;
+    }
     else if (str == "WAN")
     {
         return T_WAN;
@@ -329,6 +333,9 @@ BlackWhiteOptions::formatThresholdMethod(ThresholdFilter type)
     case T_LAAB:
         str = "laab";
         break;
+    case T_LCAM:
+        str = "lcam";
+        break;
     case T_WAN:
         str = "WAN";
         break;

src/stages/output/BlackWhiteOptions.h

@@ -26,7 +26,7 @@ class QDomElement;
 namespace output
 {
 
-enum ThresholdFilter { T_OTSU, T_MEANDELTA, T_DOTS8, T_BMTILED, T_NIBLACK, T_GATOS, T_SAUVOLA, T_WOLF, T_WINDOW, T_BRADLEY, T_NICK, T_GRAD, T_SINGH, T_FOX, T_LAAB, T_WAN, T_EDGEPLUS, T_BLURDIV, T_EDGEDIV, T_EDGEADAPT, T_ROBUST, T_GRAIN, T_MSCALE, T_ENGRAVING };
+enum ThresholdFilter { T_OTSU, T_MEANDELTA, T_DOTS8, T_BMTILED, T_NIBLACK, T_GATOS, T_SAUVOLA, T_WOLF, T_WINDOW, T_BRADLEY, T_NICK, T_GRAD, T_SINGH, T_FOX, T_LAAB, T_LCAM, T_WAN, T_EDGEPLUS, T_BLURDIV, T_EDGEDIV, T_EDGEADAPT, T_ROBUST, T_GRAIN, T_MSCALE, T_ENGRAVING };
 
 class BlackWhiteOptions
 {

src/stages/output/OptionsWidget.cpp

@@ -79,6 +79,7 @@ OptionsWidget::OptionsWidget(
     thresholdMethodSelector->addItem(tr("Singh"), T_SINGH);
     thresholdMethodSelector->addItem(tr("Fox"), T_FOX);
     thresholdMethodSelector->addItem(tr("LAAB"), T_LAAB);
+    thresholdMethodSelector->addItem(tr("LCaM"), T_LCAM);
     thresholdMethodSelector->addItem(tr("WAN"), T_WAN);
     thresholdMethodSelector->addItem(tr("EdgePlus"), T_EDGEPLUS);
     thresholdMethodSelector->addItem(tr("BlurDiv"), T_BLURDIV);
@@ -938,6 +939,7 @@ OptionsWidget::thresholdDefaultButtonClicked()
         new_radius = 10;
         new_coef = 0.75;
         break;
+    case T_LCAM:
     case T_EDGEPLUS:
     case T_BLURDIV:
     case T_EDGEDIV:

src/stages/output/OutputGenerator.cpp

@@ -1260,6 +1260,11 @@ OutputGenerator::binarize(QImage const& image, BinaryImage const& mask) const
             binarized = binarizeLAAB(gray, radius, threshold_coef, threshold_delta, bound_lower, bound_upper);
             break;
         }
+        case T_LCAM:
+        {
+            binarized = binarizeLCaM(gray, radius, threshold_coef, threshold_delta, bound_lower, bound_upper);
+            break;
+        }
         case T_WAN:
         {
             binarized = binarizeWAN(gray, radius, threshold_coef, threshold_delta, bound_lower, bound_upper);