diff --git a/config_template.json b/config_template.json
index a0f28e6..ef4aa05 100644
--- a/config_template.json
+++ b/config_template.json
@@ -98,5 +98,12 @@
         "797937_0369619_2017-09-29_0e3a_BGRN_SR_clip_aligned.tif"
     ],
     "georeference_output_folder": "processed_data/results_georeference",
-    "tile_images_output_folder": "processed_data/results_tile_images"
+    "tile_images_output_folder": "processed_data/results_tile_images",
+
+    "ndwi": {
+        "window_size": 64,
+        "blur_kernel": 9,
+        "blur_sigma": 6,
+        "majority_threshold": 0.55
+    }
 }
\ No newline at end of file
diff --git a/visualize_ndwi.py b/visualize_ndwi.py
new file mode 100644
index 0000000..3caf782
--- /dev/null
+++ b/visualize_ndwi.py
@@ -0,0 +1,356 @@
+"""
+visualize_ndwi.py
+
+Visualizes NDWI label quality for the CoastlineExtraction pipeline.
+Generates a 4-panel output: Original RGB | NDWI Heatmap | Binary Mask | Overlay
+
+Usage:
+    # Single image
+    python visualize_ndwi.py sample_data/PlanetLabs/image.tif
+
+    # Entire directory
+    python visualize_ndwi.py sample_data/PlanetLabs/
+
+    # Custom output directory
+    python visualize_ndwi.py sample_data/PlanetLabs/ --output_dir results/ndwi_viz
+"""
+
+import os
+import sys
+import argparse
+import numpy as np
+import matplotlib.pyplot as plt
+import matplotlib.patches as mpatches
+import rasterio
+import cv2
+import warnings
+
+warnings.filterwarnings("ignore", category=rasterio.errors.NotGeoreferencedWarning)
+
+from load_config import load_config
+
+
+# ── helpers ──────────────────────────────────────────────────────────────────
+
+# Default Gaussian blur parameters — matches ndwi_labels.py
+KSIZE_BLUR = (9, 9)
+SIGMA_X = 6
+SIGMA_Y = 6
+
+# Majority threshold — matches ndwi_labels.py MAJORITY_THRESHOLD
+MAJORITY_THRESHOLD = 0.55
+
+
+def load_bands(image_path):
+    """
+    Load Green (band 2) and NIR (last band) from a PlanetLabs GeoTIFF.
+    Also loads RGB (bands 3,2,1) for display.
+    Band order: 1=Blue, 2=Green, 3=Red, 4=NIR (PlanetScope)
+                1=Blue, 2=Green, 3=Red, 4=RedEdge, 5=NIR (RapidEye)
+
+    Raises:
+        ValueError: If the image has fewer than 3 bands.
+    """
+    with rasterio.open(image_path) as src:
+        if src.count < 3:
+            raise ValueError(
+                f"{image_path} has only {src.count} band(s). "
+                "Expected at least 3 (Blue, Green, Red) + NIR."
+            )
+        nir_idx = src.count          # NIR is always the last band
+        blue  = src.read(1).astype(np.float32)
+        green = src.read(2).astype(np.float32)
+        red   = src.read(3).astype(np.float32)
+        nir   = src.read(nir_idx).astype(np.float32)
+    return blue, green, red, nir
+
+
+def compute_ndwi(green, nir, blur_kernel=None, blur_sigma_x=None, blur_sigma_y=None):
+    """
+    NDWI = (Green - NIR) / (Green + NIR)
+    Returns values in [-1, 1]; positive → water, negative → land.
+
+    Gaussian blur parameters default to matching ndwi_labels.py:
+    kernel (9,9), sigmaX=6, sigmaY=6.
+
+    Args:
+        green: Green band array (float32).
+        nir: NIR band array (float32).
+        blur_kernel: Tuple (kH, kW) for GaussianBlur kernel size.
+        blur_sigma_x: Sigma X for GaussianBlur.
+        blur_sigma_y: Sigma Y for GaussianBlur.
+    """
+    if blur_kernel is None:
+        blur_kernel = KSIZE_BLUR
+    if blur_sigma_x is None:
+        blur_sigma_x = SIGMA_X
+    if blur_sigma_y is None:
+        blur_sigma_y = SIGMA_Y
+
+    np.seterr(divide='ignore', invalid='ignore')
+    ndwi = (green - nir) / (green + nir)
+    ndwi = np.nan_to_num(ndwi, nan=0.0)
+    # Gaussian blur — matches ndwi_labels.py defaults
+    ndwi = cv2.GaussianBlur(ndwi, blur_kernel, blur_sigma_x, blur_sigma_y)
+    return ndwi
+
+
+def sliding_window_otsu(ndwi, window_size=64):
+    """
+    Simplified sliding-window Otsu thresholding (pixel-grid, majority voting)
+    with global mean-threshold fallback for uncovered areas.
+
+    NOTE: This is a simplified approximation of the geometry-based sliding
+    window in ndwi_labels.py, which uses shapefile transect points as window
+    centres and rasterio.mask for extraction. Results will differ slightly.
+    This version is intended for quick visual inspection of NDWI label quality,
+    not for generating training labels.
+
+    Args:
+        ndwi: 2-D NDWI array (float, range [-1, 1]).
+        window_size: Side length of each square window in pixels.
+
+    Returns:
+        Binary mask (uint8): 1 = water, 0 = land.
+    """
+    h, w = ndwi.shape
+    vote_map  = np.zeros((h, w), dtype=np.int32)
+    count_map = np.zeros((h, w), dtype=np.int32)
+
+    # Convert NDWI [-1,1] to uint8 matching ndwi_labels.py: (ndwi * 127) + 128
+    # NDWI = 0 maps to 128; water (positive NDWI) > 128; land (negative) < 128
+    ndwi_8bit = np.clip((ndwi * 127) + 128, 0, 255).astype(np.uint8)
+
+    otsu_thresholds = []   # collect valid thresholds for global fallback
+    step = window_size // 2
+    for y in range(0, h, step):
+        for x in range(0, w, step):
+            window = ndwi_8bit[y:y + window_size, x:x + window_size]
+            if window.size == 0:
+                continue
+            # Skip nearly-uniform windows — Otsu on single-class data
+            # (e.g. all-land) produces a meaningless threshold that splits
+            # land texture noise as "water", causing scattered white pixels.
+            # A std of 10 in uint8 space filters out windows that contain
+            # only one class (pure land ≈ std 3–8, pure water ≈ std 5–10).
+            if window.std() < 10:
+                continue
+            thresh, _ = cv2.threshold(
+                window, 0, 1,
+                cv2.THRESH_BINARY + cv2.THRESH_OTSU
+            )
+            otsu_thresholds.append(thresh)
+            classified = (window >= thresh).astype(np.int32)
+            vote_map[y:y + window_size, x:x + window_size]  += classified
+            count_map[y:y + window_size, x:x + window_size] += 1
+
+    # Majority vote for pixels covered by valid sliding windows
+    # Threshold matches ndwi_labels.py MAJORITY_THRESHOLD (0.55)
+    safe_count = np.where(count_map == 0, 1, count_map)
+    mask = (vote_map / safe_count >= MAJORITY_THRESHOLD).astype(np.uint8)
+
+    # For uncovered pixels, fall back to a global mean threshold.
+    # This matches ndwi_labels.py's concatenation logic: sliding-window
+    # labels where windows exist, single mean-threshold classification
+    # elsewhere.  The +10 offset biases toward land, matching ndwi_labels.py.
+    if otsu_thresholds:
+        mean_thresh = np.mean(otsu_thresholds) + 10
+        global_mask = (ndwi_8bit >= mean_thresh).astype(np.uint8)
+        covered = count_map > 0
+        mask = np.where(covered, mask, global_mask)
+    else:
+        # No valid windows — use a single global Otsu threshold
+        global_thresh, _ = cv2.threshold(
+            ndwi_8bit, 0, 1, cv2.THRESH_BINARY + cv2.THRESH_OTSU
+        )
+        mask = (ndwi_8bit >= global_thresh).astype(np.uint8)
+
+    return mask
+
+
+def normalize_for_display(arr):
+    """Stretch array to [0, 1] for display."""
+    lo, hi = arr.min(), arr.max()
+    if hi == lo:
+        return np.zeros_like(arr, dtype=np.float32)
+    return (arr - lo) / (hi - lo)
+
+
+def build_rgb(red, green, blue):
+    """Stack and percentile-stretch to a display-ready RGB image."""
+    rgb = np.stack([red, green, blue], axis=-1)
+    lo, hi = np.percentile(rgb, 2), np.percentile(rgb, 98)
+    rgb = np.clip((rgb - lo) / (hi - lo + 1e-9), 0, 1)
+    return rgb
+
+
+def print_ndwi_stats(ndwi, binary_mask, image_name):
+    """Print statistics to help tune thresholds."""
+    water_pct = binary_mask.mean() * 100
+    print(f"\n── NDWI Stats: {image_name} ──")
+    print(f"  Min  : {ndwi.min():.4f}")
+    print(f"  Max  : {ndwi.max():.4f}")
+    print(f"  Mean : {ndwi.mean():.4f}")
+    print(f"  Std  : {ndwi.std():.4f}")
+    print(f"  Water pixels : {water_pct:.1f}%")
+    print(f"  Land  pixels : {100 - water_pct:.1f}%")
+
+
+# ── main visualisation ────────────────────────────────────────────────────────
+
+def visualize_single(image_path, output_dir, window_size):
+    """
+    Generate and save a 4-panel NDWI visualisation for one image.
+    Panels: Original RGB | NDWI Heatmap | Binary Mask | Overlay
+    """
+    image_name = os.path.splitext(os.path.basename(image_path))[0]
+    os.makedirs(output_dir, exist_ok=True)
+
+    # 1. Load bands
+    blue, green, red, nir = load_bands(image_path)
+
+    # 2. Compute NDWI + binary mask
+    ndwi        = compute_ndwi(green, nir)
+    binary_mask = sliding_window_otsu(ndwi, window_size=window_size)
+
+    # 3. Stats
+    print_ndwi_stats(ndwi, binary_mask, image_name)
+
+    # 4. Build display arrays
+    rgb          = build_rgb(red, green, blue)
+    ndwi_display = normalize_for_display(ndwi)
+
+    # Colour overlay: water=blue, land=tan
+    overlay = rgb.copy()
+    overlay[binary_mask == 1] = [0.20, 0.45, 0.85]   # blue  → water
+    overlay[binary_mask == 0] = overlay[binary_mask == 0] * 0.6 + np.array([0.6, 0.5, 0.3]) * 0.4
+
+    # 5. Plot
+    fig, axes = plt.subplots(1, 4, figsize=(20, 5))
+    fig.suptitle(f"NDWI Label Quality — {image_name}", fontsize=13, fontweight='bold')
+
+    axes[0].imshow(rgb)
+    axes[0].set_title("Original RGB")
+    axes[0].axis('off')
+
+    im = axes[1].imshow(ndwi_display, cmap='RdYlBu', vmin=0, vmax=1)
+    axes[1].set_title("NDWI Heatmap\n(blue=water, red=land)")
+    axes[1].axis('off')
+    fig.colorbar(im, ax=axes[1], fraction=0.046, pad=0.04)
+
+    axes[2].imshow(binary_mask, cmap='gray', vmin=0, vmax=1)
+    axes[2].set_title("Binary Mask\n(white=water, black=land)")
+    axes[2].axis('off')
+
+    axes[3].imshow(overlay)
+    axes[3].set_title("Overlay")
+    axes[3].axis('off')
+    water_patch = mpatches.Patch(color=[0.20, 0.45, 0.85], label='Water')
+    axes[3].legend(handles=[water_patch], loc='lower right', fontsize=8)
+
+    plt.tight_layout()
+
+    out_path = os.path.join(output_dir, f"{image_name}_ndwi_viz.png")
+    plt.savefig(out_path, dpi=150, bbox_inches='tight')
+    plt.close()
+    print(f"  Saved → {out_path}")
+    return out_path
+
+
+def visualize_directory(input_dir, output_dir, window_size):
+    """Process all .tif files in a directory."""
+    tif_files = [
+        os.path.join(input_dir, f)
+        for f in sorted(os.listdir(input_dir))
+        if f.lower().endswith('.tif') and 'udm' not in f.lower()
+    ]
+    if not tif_files:
+        print(f"No .tif files found in {input_dir}")
+        return
+
+    print(f"Found {len(tif_files)} image(s) in {input_dir}")
+    for path in tif_files:
+        print(f"\nProcessing: {os.path.basename(path)}")
+        try:
+            visualize_single(path, output_dir, window_size)
+        except Exception as e:
+            print(f"  ERROR: {e}")
+
+
+# ── CLI ───────────────────────────────────────────────────────────────────────
+
+def parse_args():
+    parser = argparse.ArgumentParser(
+        description="Visualize NDWI label quality for CoastlineExtraction pipeline."
+    )
+    parser.add_argument(
+        "input",
+        help="Path to a single .tif image or a directory of .tif images."
+    )
+    parser.add_argument(
+        "--output_dir",
+        default="ndwi_visualizations",
+        help="Directory to save PNG outputs (default: ndwi_visualizations/)."
+    )
+    parser.add_argument(
+        "--window_size",
+        type=int,
+        default=None,
+        help="Sliding window size for Otsu thresholding (default: from config or 64)."
+    )
+    parser.add_argument(
+        "--blur_kernel",
+        type=int,
+        default=None,
+        help="Gaussian blur kernel size, e.g. 9 for (9,9) (default: from config or 9)."
+    )
+    parser.add_argument(
+        "--blur_sigma",
+        type=float,
+        default=None,
+        help="Gaussian blur sigma (default: from config or 6)."
+    )
+    return parser.parse_args()
+
+
+def main():
+    args = parse_args()
+
+    # Load NDWI parameters from config, with CLI overrides
+    try:
+        config = load_config()
+        ndwi_cfg = config.get("ndwi", {})
+    except Exception:
+        ndwi_cfg = {}
+
+    window_size = args.window_size or ndwi_cfg.get("window_size", 64)
+
+    blur_k = args.blur_kernel or ndwi_cfg.get("blur_kernel", 9)
+    blur_kernel = (blur_k, blur_k)
+
+    blur_sigma = args.blur_sigma
+    if blur_sigma is None:
+        blur_sigma = ndwi_cfg.get("blur_sigma", 6)
+    blur_sigma_x = blur_sigma
+    blur_sigma_y = blur_sigma
+
+    # Stash in module-level defaults so compute_ndwi picks them up
+    global KSIZE_BLUR, SIGMA_X, SIGMA_Y
+    KSIZE_BLUR = blur_kernel
+    SIGMA_X = int(blur_sigma_x)
+    SIGMA_Y = int(blur_sigma_y)
+
+    print(f"Using window_size={window_size}, blur_kernel={blur_kernel}, "
+          f"blur_sigma=({blur_sigma_x}, {blur_sigma_y})")
+
+    if os.path.isdir(args.input):
+        visualize_directory(args.input, args.output_dir, window_size)
+    elif os.path.isfile(args.input):
+        visualize_single(args.input, args.output_dir, window_size)
+    else:
+        print(f"ERROR: '{args.input}' is not a valid file or directory.")
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file