MASI4-signal-processing/src/main/java/domain/image/processing/threshold/Thresholding.java

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);
    }
}