カラー量子化用に提供されている Java コードが、特に 256 色を超える画像を 256 色に減色する場合に効果的に減色するのに苦労し、次のような顕著なエラーが発生するのはなぜですか?

import java.util.Arrays;
import java.util.Comparator;
import java.awt.image.BufferedImage;

public class MedianCutQuantizer {

    public static void quantize(BufferedImage image, int colors) {
        int[] pixels = image.getRGB(0, 0, image.getWidth(), image.getHeight(), null, 0, image.getWidth());
        Arrays.sort(pixels); // Sort pixels by red, green, and blue channel values

        // Create a binary tree representation of the color space
        TreeNode root = new TreeNode(pixels);

        // Recursively divide the color space and create the palette
        TreeNode[] palette = new TreeNode[colors];
        for (int i = 0; i < colors; i++) {
            palette[i] = root;
            root = divide(root);
        }

        // Replace pixels with their corresponding palette colors
        for (int i = 0; i < pixels.length; i++) {
            pixels[i] = getClosestColor(pixels[i], palette);
        }

        image.setRGB(0, 0, image.getWidth(), image.getHeight(), pixels, 0, image.getWidth());
    }

    private static TreeNode divide(TreeNode node) {
        // Find the median color value
        int median = node.getMedianValue();

        // Create two new nodes, one for each half of the color range
        TreeNode left = new TreeNode();
        TreeNode right = new TreeNode();

        // Divide the pixels into two halves
        for (int i = node.start; i < node.end; i++) {
            if (node.pixels[i] <= median) {
                left.addPixel(node.pixels[i]);
            } else {
                right.addPixel(node.pixels[i]);
            }
        }

        return left.count > right.count ? left : right;
    }

    private static int getClosestColor(int pixel, TreeNode[] palette) {
        int minDistance = Integer.MAX_VALUE;
        int closestColor = 0;

        for (TreeNode node : palette) {
            int distance = getDistance(pixel, node.getAverageValue());
            if (distance < minDistance) {
                minDistance = distance;
                closestColor = node.getAverageValue();
            }
        }

        return closestColor;
    }

    // Utility methods

    private static int getDistance(int color1, int color2) {
        int r1 = (color1 >> 16) & 0xFF;
        int g1 = (color1 >> 8) & 0xFF;
        int b1 = color1 & 0xFF;

        int r2 = (color2 >> 16) & 0xFF;
        int g2 = (color2 >> 8) & 0xFF;
        int b2 = color2 & 0xFF;

        return (r1 - r2) * (r1 - r2) + (g1 - g2) * (g1 - g2) + (b1 - b2) * (b1 - b2);
    }

    private static class TreeNode {
        int start;
        int end;
        int count;
        int[] pixels;
        Integer averageValue;

        public TreeNode() {
            this(new int[0], 0, 0);
        }

        public TreeNode(int[] pixels, int start, int end) {
            this.pixels = pixels;
            this.start = start;
            this.end = end;

            count = end - start;
        }

        public int getMedianValue() {
            return pixels[(start + end) / 2];
        }

        public int getAverageValue() {
            if (averageValue == null) {
                int r = 0;
                int g = 0;
                int b = 0;

                for (int i = start; i < end; i++) {
                    int pixel = pixels[i];

                    r += (pixel >> 16) & 0xFF;
                    g += (pixel >> 8) & 0xFF;
                    b += pixel & 0xFF;
                }

                averageValue = (r / count) << 16 | (g / count) << 8 | b / count;
            }

            return averageValue;
        }

        public void addPixel(int pixel) {
            int[] newPixels = new int[pixels.length + 1];

            System.arraycopy(pixels, start, newPixels, start, end);
            newPixels[end] = pixel;

            pixels = newPixels;
            end++;
            count = end - start;

            averageValue = null;
        }
    }
}