diff --git a/HW01/.gitignore b/HW01/.gitignore
index 6fcf43c..303b4a8 100644
--- a/HW01/.gitignore
+++ b/HW01/.gitignore
@@ -1,2 +1,5 @@
+# Python execution related
+__pycache__/
+
 # IDE files
 .idea/
diff --git a/HW01/scripts/demo.py b/HW01/scripts/demo.py
new file mode 100644
index 0000000..a9e8291
--- /dev/null
+++ b/HW01/scripts/demo.py
@@ -0,0 +1,90 @@
+#
+# Digital Image Processing HW01 assignment demo file
+#
+#
+# author: Christos Choutouridis <cchoutou@ece.auth.gr>
+# date:   29/04/2025
+#
+
+try:
+    import os
+    import numpy as np
+    import matplotlib.pyplot as plt
+    from PIL import Image
+except ImportError as e:
+    print("Missing package: ", e)
+    print("Run: pip install -r requirements.txt to install.")
+    exit(1)
+
+from hist_utils import calculate_hist_of_img
+from hist_modif import perform_hist_eq, perform_hist_matching
+
+# Define filenames
+input_filename = "input_img.jpg"
+ref_filename = "ref_img.jpg"
+
+# Load images
+input_img = Image.open(input_filename).convert("L")
+ref_img = Image.open(ref_filename).convert("L")
+
+# Convert to numpy arrays in [0,1]
+input_array = np.array(input_img).astype(float) / 255.0
+ref_array = np.array(ref_img).astype(float) / 255.0
+
+# Create output directory
+os.makedirs("demo_outputs", exist_ok=True)
+
+
+
+
+def plot_comparison(input_array, output_array, title, filename):
+    """
+    Create a 2x2 plot: input image, output image, input histogram, output histogram.
+    Save it to filename.
+    """
+    fig, axes = plt.subplots(2, 2, figsize=(10, 8))
+
+    # Plot input image
+    axes[0, 0].imshow(input_array, cmap="gray", vmin=0, vmax=1)
+    axes[0, 0].set_title("Input Image")
+    axes[0, 0].axis("off")
+
+    # Plot output image
+    axes[0, 1].imshow(output_array, cmap="gray", vmin=0, vmax=1)
+    axes[0, 1].set_title("Output Image")
+    axes[0, 1].axis("off")
+
+    # Plot input histogram
+    input_hist = calculate_hist_of_img(input_array, return_normalized=True)
+    axes[1, 0].bar(list(input_hist.keys()), list(input_hist.values()), width=0.01)
+    axes[1, 0].set_title("Input Histogram")
+
+    # Plot output histogram
+    output_hist = calculate_hist_of_img(output_array, return_normalized=True)
+    axes[1, 1].bar(list(output_hist.keys()), list(output_hist.values()), width=0.01)
+    axes[1, 1].set_title("Output Histogram")
+
+    # Set overall title
+    fig.suptitle(title, fontsize=16)
+
+    # Adjust layout
+    plt.tight_layout(rect=[0, 0, 1, 0.95])
+
+    # Save
+    plt.savefig(filename)
+    plt.close()
+
+# Modes to test
+modes = ["greedy", "non-greedy", "post-disturbance"]
+
+# Run equalization
+for mode in modes:
+    equalized_img = perform_hist_eq(input_array, mode)
+    out_filename = f"demo_outputs/equalization_{mode}.png"
+    plot_comparison(input_array, equalized_img, f"Histogram Equalization ({mode})", out_filename)
+
+# Run matching
+for mode in modes:
+    matched_img = perform_hist_matching(input_array, ref_array, mode)
+    out_filename = f"demo_outputs/matching_{mode}.png"
+    plot_comparison(input_array, matched_img, f"Histogram Matching ({mode})", out_filename)
diff --git a/HW01/scripts/demo_outputs/equalization_greedy.png b/HW01/scripts/demo_outputs/equalization_greedy.png
new file mode 100644
index 0000000..2fb9d6a
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diff --git a/HW01/scripts/demo_outputs/equalization_non-greedy.png b/HW01/scripts/demo_outputs/equalization_non-greedy.png
new file mode 100644
index 0000000..1ccd87a
Binary files /dev/null and b/HW01/scripts/demo_outputs/equalization_non-greedy.png differ
diff --git a/HW01/scripts/demo_outputs/equalization_post-disturbance.png b/HW01/scripts/demo_outputs/equalization_post-disturbance.png
new file mode 100644
index 0000000..cdcb37b
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diff --git a/HW01/scripts/demo_outputs/matching_greedy.png b/HW01/scripts/demo_outputs/matching_greedy.png
new file mode 100644
index 0000000..80854a8
Binary files /dev/null and b/HW01/scripts/demo_outputs/matching_greedy.png differ
diff --git a/HW01/scripts/demo_outputs/matching_non-greedy.png b/HW01/scripts/demo_outputs/matching_non-greedy.png
new file mode 100644
index 0000000..1374719
Binary files /dev/null and b/HW01/scripts/demo_outputs/matching_non-greedy.png differ
diff --git a/HW01/scripts/demo_outputs/matching_post-disturbance.png b/HW01/scripts/demo_outputs/matching_post-disturbance.png
new file mode 100644
index 0000000..e64194c
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diff --git a/HW01/scripts/hist_modif.py b/HW01/scripts/hist_modif.py
index e69de29..e5a0e94 100644
--- a/HW01/scripts/hist_modif.py
+++ b/HW01/scripts/hist_modif.py
@@ -0,0 +1,373 @@
+#
+# histogram modification file
+#
+#
+# author: Christos Choutouridis <cchoutou@ece.auth.gr>
+# date:   29/04/2025
+#
+
+try:
+    import numpy as np
+except ImportError as e:
+    print("Missing package: ", e)
+    print("Run: pip install -r requirements.txt to install.")
+    exit(1)
+
+import hist_utils
+
+
+def perform_hist_modification(
+        img_array: np.ndarray,
+        hist_ref: dict,
+        mode: str,
+        L: int = 256
+) -> np.ndarray:
+    """
+    Perform histogram modification on an image according to the desired histogram and selected mode.
+
+    Args:
+        img_array (np.ndarray): Input grayscale image with float values in [0, 1].
+        hist_ref (dict): Desired output histogram (levels -> relative frequencies).
+        mode (str): One of ["greedy", "non-greedy", "post-disturbance"].
+        L (int):    Number of levels to clip
+    Returns:
+        np.ndarray: Modified image array.
+    """
+    if mode not in ["greedy", "non-greedy", "post-disturbance"]:
+        raise ValueError(f"Unknown mode: {mode}")
+
+    # Step 1: Optional post-disturbance (add noise)
+    if mode == "post-disturbance":
+        unique_levels = np.unique(img_array)
+        if len(unique_levels) < 2:
+            raise ValueError("Post-disturbance mode requires at least two unique input levels.")
+
+        d = unique_levels[1] - unique_levels[0]
+        noise = np.random.uniform(-d / 2, d / 2, size=img_array.shape)
+
+        # Add noise
+        img_array = img_array + noise
+
+        # Clip to [0, 1] and quantize to 256 levels to avoid infinite precision
+        img_array = np.clip(img_array, 0, 1)
+        img_array = np.round(img_array * L) / float(L)
+
+    # Step 2: Calculate input histogram (not normalized)
+    input_hist = hist_utils.calculate_hist_of_img(img_array, return_normalized=False)
+
+    # Step 3: Build the modification transform
+    modification_transform = {}
+
+    # Prepare input levels (sorted)
+    input_levels = sorted(input_hist.keys())
+    input_counts = [input_hist[level] for level in input_levels]
+
+    # Prepare target output levels and target counts
+    output_levels = sorted(hist_ref.keys())
+    output_frequencies = [hist_ref[level] for level in output_levels]
+    total_samples = sum(input_counts)
+    output_target_counts = [freq * total_samples for freq in output_frequencies]
+
+    # Initialize pointers
+    in_idx = 0
+    out_idx = 0
+    current_in_count = 0
+    current_out_target = output_target_counts[out_idx]
+
+    while in_idx < len(input_levels):
+        in_level = input_levels[in_idx]
+        in_count = input_counts[in_idx]
+
+        if mode in ["greedy", "post-disturbance"]:
+            if current_in_count + in_count <= current_out_target:
+                modification_transform[in_level] = output_levels[out_idx]
+                current_in_count += in_count
+                in_idx += 1
+            else:
+                out_idx += 1
+                if out_idx < len(output_levels):
+                    current_out_target = output_target_counts[out_idx]
+                    current_in_count = 0
+                else:
+                    # No more output levels: assign the rest to the last output level
+                    for remaining_idx in range(in_idx, len(input_levels)):
+                        modification_transform[input_levels[remaining_idx]] = output_levels[-1]
+                    break
+
+        elif mode == "non-greedy":
+            deficiency = current_out_target - current_in_count
+            if deficiency >= in_count / 2:
+                modification_transform[in_level] = output_levels[out_idx]
+                current_in_count += in_count
+                in_idx += 1
+            else:
+                out_idx += 1
+                if out_idx < len(output_levels):
+                    current_out_target = output_target_counts[out_idx]
+                    current_in_count = 0
+                else:
+                    # No more output levels: assign the rest to the last output level
+                    for remaining_idx in range(in_idx, len(input_levels)):
+                        modification_transform[input_levels[remaining_idx]] = output_levels[-1]
+                    break
+
+    # Step 4: Apply the transform
+    modified_img = hist_utils.apply_hist_modification_transform(img_array, modification_transform)
+
+    return modified_img
+
+
+def perform_hist_eq(
+    img_array: np.ndarray,
+    mode: str,
+    L: int = 256  # number of levels to use for output
+) -> np.ndarray:
+    """
+    Perform histogram equalization on an input image according to the selected mode.
+
+    Args:
+        img_array (np.ndarray): Input grayscale image with float values in [0, 1].
+        mode (str):             One of ["greedy", "non-greedy", "post-disturbance"].
+        L (int):                Number of levels to use for output
+    Returns:
+        np.ndarray: Equalized image array.
+    """
+    # Step 1: define L uniformly spaced output levels
+    output_levels = np.linspace(0, 1, L)
+    hist_ref = {level: 1.0 / L for level in output_levels}
+
+    # Step 2: call the generic modification function
+    equalized_img = perform_hist_modification(img_array, hist_ref, mode)
+
+    return equalized_img
+
+
+def perform_hist_matching(
+    img_array: np.ndarray,
+    img_array_ref: np.ndarray,
+    mode: str
+) -> np.ndarray:
+    """
+    Perform histogram matching of img_array to match img_array_ref according to the selected mode.
+
+    Args:
+        img_array (np.ndarray):     Input grayscale image.
+        img_array_ref (np.ndarray): Reference grayscale image.
+        mode (str):                 One of ["greedy", "non-greedy", "post-disturbance"].
+
+    Returns:
+        np.ndarray: Processed image with histogram matched to the reference.
+    """
+    # Step 1: Calculate the normalized histogram of the reference image
+    ref_hist = hist_utils.calculate_hist_of_img(img_array_ref, return_normalized=True)
+
+    # Step 2: Perform histogram modification
+    processed_img = perform_hist_modification(img_array, ref_hist, mode)
+
+    return processed_img
+
+
+
+#
+# =========================== Functional tests ===========================
+#
+# To execute the tests run:
+#   python hist_modif.py
+#
+
+def test_perform_hist_modification_greedy():
+    """
+    Test perform_hist_modification with mode 'greedy' on a simple 3x3 image.
+    """
+    img = np.array([
+        [0.0, 0.0, 0.5],
+        [0.5, 1.0, 1.0],
+        [1.0, 0.5, 0.0]
+    ])
+
+    hist_ref = {
+        0.25: 0.5,
+        0.75: 0.5
+    }
+
+    modified_img = perform_hist_modification(img, hist_ref, mode="greedy")
+
+    modified_hist = hist_utils.calculate_hist_of_img(modified_img, return_normalized=True)
+
+    print("Mode: greedy")
+    print("Modified image:\n", modified_img)
+    print("Modified histogram:", modified_hist)
+
+    output_levels = set(modified_hist.keys())
+    expected_levels = {0.25, 0.75}
+    print("Test passed:", output_levels == expected_levels)
+    print()
+
+
+def test_perform_hist_modification_non_greedy():
+    """
+    Test perform_hist_modification with mode 'non-greedy' on a simple 3x3 image.
+    """
+    img = np.array([
+        [0.0, 0.0, 0.5],
+        [0.5, 1.0, 1.0],
+        [1.0, 0.5, 0.0]
+    ])
+
+    hist_ref = {
+        0.2: 0.4,
+        0.8: 0.6
+    }
+
+    modified_img = perform_hist_modification(img, hist_ref, mode="non-greedy")
+
+    modified_hist = hist_utils.calculate_hist_of_img(modified_img, return_normalized=True)
+
+    print("Mode: non-greedy")
+    print("Modified image:\n", modified_img)
+    print("Modified histogram:", modified_hist)
+
+    output_levels = set(modified_hist.keys())
+    expected_levels = {0.2, 0.8}
+    print("Test passed:", output_levels == expected_levels)
+    print()
+
+
+def test_perform_hist_modification_post_disturbance():
+    """
+    Test perform_hist_modification with mode 'post-disturbance' on a simple 3x3 image.
+    """
+    img = np.array([
+        [0.0, 0.0, 0.5],
+        [0.5, 1.0, 1.0],
+        [1.0, 0.5, 0.0]
+    ])
+
+    hist_ref = {
+        0.3: 0.5,
+        0.7: 0.5
+    }
+
+    modified_img = perform_hist_modification(img, hist_ref, mode="post-disturbance")
+
+    modified_hist = hist_utils.calculate_hist_of_img(modified_img, return_normalized=True)
+
+    print("Mode: post-disturbance")
+    print("Modified image:\n", modified_img)
+    print("Modified histogram:", modified_hist)
+
+    output_levels = set(modified_hist.keys())
+    expected_levels = {0.3, 0.7}
+    print("Test passed:", output_levels == expected_levels)
+    print()
+
+
+
+def test_perform_hist_eq_all_modes():
+    """
+    Test perform_hist_eq for all modes on a simple 3x3 image.
+    """
+    img = np.array([
+        [0.0, 0.0, 0.5],
+        [0.5, 1.0, 1.0],
+        [1.0, 0.5, 0.0]
+    ])
+
+    for mode in ["greedy", "non-greedy", "post-disturbance"]:
+        print(f"Mode: {mode} (histogram equalization)")
+
+        equalized_img = perform_hist_eq(img, mode=mode)
+        equalized_hist = hist_utils.calculate_hist_of_img(equalized_img, return_normalized=True)
+
+        print("Equalized image:\n", equalized_img)
+        print("Equalized histogram:", equalized_hist)
+
+        levels = list(equalized_hist.keys())
+        freqs = list(equalized_hist.values())
+        expected_freq = 1.0 / len(levels)
+
+        uniform_distribution = all(np.isclose(freq, expected_freq, atol=1e-2) for freq in freqs)
+        print("Test passed:", uniform_distribution)
+        print()
+
+
+
+def test_perform_hist_matching_all_modes():
+    """
+    Test perform_hist_matching for all modes on a simple 3x3 image.
+    """
+    img = np.array([
+        [0.0, 0.0, 0.5],
+        [0.5, 1.0, 1.0],
+        [1.0, 0.5, 0.0]
+    ])
+
+    # Reference image (different histogram)
+    ref_img = np.array([
+        [0.2, 0.2, 0.2],
+        [0.8, 0.8, 0.8],
+        [0.8, 0.2, 0.2]
+    ])
+
+    for mode in ["greedy", "non-greedy", "post-disturbance"]:
+        print(f"Mode: {mode} (histogram matching)")
+
+        matched_img = perform_hist_matching(img, ref_img, mode=mode)
+        matched_hist = hist_utils.calculate_hist_of_img(matched_img, return_normalized=True)
+        ref_hist = hist_utils.calculate_hist_of_img(ref_img, return_normalized=True)
+
+        print("Matched image:\n", matched_img)
+        print("Matched histogram:", matched_hist)
+        print("Reference histogram:", ref_hist)
+
+        matched_levels = set(matched_hist.keys())
+        ref_levels = set(ref_hist.keys())
+
+        # Check if output levels are the same as the reference levels
+        print("Test passed:", matched_levels == ref_levels)
+        print()
+
+
+def test_perform_hist_matching_simple():
+    """
+    Simple test for perform_hist_matching function.
+    """
+    # Create a small input image
+    img = np.array([
+        [0.0, 0.5],
+        [1.0, 0.5]
+    ])
+
+    # Create a reference image with known distribution
+    ref_img = np.array([
+        [0.25, 0.25],
+        [0.75, 0.75]
+    ])
+
+    # Perform histogram matching using greedy mode
+    matched_img = perform_hist_matching(img, ref_img, mode="greedy")
+
+    # Calculate histograms
+    matched_hist = hist_utils.calculate_hist_of_img(matched_img, return_normalized=True)
+    ref_hist = hist_utils.calculate_hist_of_img(ref_img, return_normalized=True)
+
+    print("Simple test for perform_hist_matching")
+    print("Matched image:\n", matched_img)
+    print("Matched histogram:", matched_hist)
+    print("Reference histogram:", ref_hist)
+
+    # Check if output levels are same as reference levels
+    matched_levels = set(matched_hist.keys())
+    ref_levels = set(ref_hist.keys())
+
+    print("Test passed:", matched_levels == ref_levels)
+    print()
+
+
+if __name__ == '__main__':
+    test_perform_hist_modification_greedy()
+    test_perform_hist_modification_non_greedy()
+    test_perform_hist_modification_post_disturbance()
+    test_perform_hist_eq_all_modes()
+    test_perform_hist_matching_all_modes()
+    test_perform_hist_matching_simple()
\ No newline at end of file
diff --git a/HW01/scripts/hist_utils.py b/HW01/scripts/hist_utils.py
index 2b64c81..981361b 100644
--- a/HW01/scripts/hist_utils.py
+++ b/HW01/scripts/hist_utils.py
@@ -8,7 +8,6 @@
 
 try:
     import numpy as np
-    from PIL import Image
 except ImportError as e:
     print("Missing package: ", e)
     print("Run: pip install -r requirements.txt to install.")
diff --git a/HW01/scripts/input_img.jpg b/HW01/scripts/input_img.jpg
new file mode 100644
index 0000000..4b25274
Binary files /dev/null and b/HW01/scripts/input_img.jpg differ
diff --git a/HW01/scripts/ref_img.jpg b/HW01/scripts/ref_img.jpg
new file mode 100644
index 0000000..a7a9dc9
Binary files /dev/null and b/HW01/scripts/ref_img.jpg differ
diff --git a/HW01/scripts/requirements.txt b/HW01/scripts/requirements.txt
index 0d59398..e9994ae 100644
--- a/HW01/scripts/requirements.txt
+++ b/HW01/scripts/requirements.txt
@@ -1,2 +1,4 @@
 numpy
 Pillow
+matplotlib
+