Add thresholding

src/main/java/domain/image/processing/threshold/Thresholding.java

@@ -0,0 +1,116 @@
+package domain.image.processing.threshold;
+
+import domain.image.GrayScaleMatrix;
+import domain.image.Image;
+
+public class Thresholding {
+
+    public static GrayScaleMatrix simpleThreshold(
+            Image image,
+            int threshold
+    ) {
+        GrayScaleMatrix gray = image.toGrayScale();
+
+        int height = gray.getHeight();
+        int width = gray.getWidth();
+
+        double[][] data = gray.getRawData();
+        double[][] result = new double[height][width];
+
+        for (int y = 0; y < height; y++) {
+            for (int x = 0; x < width; x++) {
+                result[y][x] = data[y][x] >= threshold
+                        ? 255
+                        : 0;
+            }
+        }
+
+        return new GrayScaleMatrix(result);
+    }
+
+    public static GrayScaleMatrix doubleThreshold(
+            Image image,
+            int threshold1,
+            int threshold2
+    ) {
+        if (threshold1 > threshold2) {
+            int temp = threshold1;
+            threshold1 = threshold2;
+            threshold2 = temp;
+        }
+
+        GrayScaleMatrix gray = image.toGrayScale();
+
+        int height = gray.getHeight();
+        int width = gray.getWidth();
+
+        double[][] data = gray.getRawData();
+        double[][] result = new double[height][width];
+
+        for (int y = 0; y < height; y++) {
+            for (int x = 0; x < width; x++) {
+
+                double value = data[y][x];
+
+                if (value < threshold1) {
+                    result[y][x] = 0;
+                } else if (value < threshold2) {
+                    result[y][x] = 127;
+                } else {
+                    result[y][x] = 255;
+                }
+            }
+        }
+
+        return new GrayScaleMatrix(result);
+    }
+
+    public static GrayScaleMatrix automaticThreshold(Image image) {
+        GrayScaleMatrix gray = image.toGrayScale();
+
+        double[][] data = gray.getRawData();
+
+        double threshold = (gray.getMinValue() + gray.getMaxValue()) / 2.0;
+
+        while (true) {
+            double lowerSum = 0;
+            double upperSum = 0;
+
+            int lowerCount = 0;
+            int upperCount = 0;
+
+            for (int y = 0; y < gray.getHeight(); y++) {
+                for (int x = 0; x < gray.getWidth(); x++) {
+
+                    double value = data[y][x];
+
+                    if (value <= threshold) {
+                        lowerSum += value;
+                        lowerCount++;
+                    } else {
+                        upperSum += value;
+                        upperCount++;
+                    }
+                }
+            }
+
+            if (lowerCount == 0 || upperCount == 0) {
+                break;
+            }
+
+            double lowerMean = lowerSum / lowerCount;
+            double upperMean = upperSum / upperCount;
+
+            double newThreshold = (lowerMean + upperMean) / 2.0;
+
+            if (Math.abs(newThreshold - threshold) < 0.5) {
+                threshold = newThreshold;
+                break;
+            }
+
+            threshold = newThreshold;
+        }
+
+        return simpleThreshold(image, (int) threshold);
+    }
+}