diff --git a/tests/test_main_utils.py b/tests/test_main_utils.py
new file mode 100644
index 0000000..22e323f
--- /dev/null
+++ b/tests/test_main_utils.py
@@ -0,0 +1,166 @@
+"""Tests for spritegrid.main utility functions: load_image, handle_txt, handle_png, create_downsampled_image."""
+
+import os
+import sys
+from io import BytesIO
+from unittest.mock import patch, MagicMock
+
+import numpy as np
+import pytest
+from PIL import Image
+
+
+# ---------------------------------------------------------------------------
+# load_image
+# ---------------------------------------------------------------------------
+
+class TestLoadImage:
+    def test_load_local_file(self, tmp_path):
+        from spritegrid.main import load_image
+        img_path = str(tmp_path / "test.png")
+        Image.new("RGB", (4, 4), (255, 0, 0)).save(img_path)
+        result = load_image(img_path)
+        assert isinstance(result, Image.Image)
+        assert result.size == (4, 4)
+
+    def test_missing_local_file_returns_none(self, tmp_path, capsys):
+        from spritegrid.main import load_image
+        result = load_image(str(tmp_path / "nonexistent.png"))
+        assert result is None
+
+    def test_url_loads_image(self):
+        from spritegrid.main import load_image
+        mock_response = MagicMock()
+        mock_response.headers = {"content-type": "image/png"}
+        # Create a fake PNG in memory
+        buf = BytesIO()
+        Image.new("RGB", (2, 2), (0, 255, 0)).save(buf, format="PNG")
+        mock_response.content = buf.getvalue()
+        mock_response.raise_for_status = MagicMock()
+
+        with patch("requests.get", return_value=mock_response):
+            result = load_image("http://example.com/img.png")
+        assert isinstance(result, Image.Image)
+
+    def test_url_wrong_content_type_returns_none(self, capsys):
+        from spritegrid.main import load_image
+        mock_response = MagicMock()
+        mock_response.headers = {"content-type": "text/html"}
+        mock_response.raise_for_status = MagicMock()
+
+        with patch("requests.get", return_value=mock_response):
+            result = load_image("http://example.com/page.html")
+        assert result is None
+
+
+# ---------------------------------------------------------------------------
+# handle_txt
+# ---------------------------------------------------------------------------
+
+class TestHandleTxt:
+    def test_writes_content_to_file(self, tmp_path):
+        from spritegrid.main import handle_txt
+        path = str(tmp_path / "output.txt")
+        handle_txt("hello world", path)
+        assert open(path).read() == "hello world"
+
+    def test_non_txt_extension_warns(self, tmp_path, capsys):
+        from spritegrid.main import handle_txt
+        path = str(tmp_path / "output.ansi")
+        handle_txt("content", path)
+        out = capsys.readouterr().out
+        assert "Warning" in out
+
+    def test_txt_extension_no_warning(self, tmp_path, capsys):
+        from spritegrid.main import handle_txt
+        path = str(tmp_path / "output.txt")
+        handle_txt("content", path)
+        out = capsys.readouterr().out
+        assert "Warning" not in out
+
+    def test_creates_file_if_not_exists(self, tmp_path):
+        from spritegrid.main import handle_txt
+        path = str(tmp_path / "new.txt")
+        assert not os.path.exists(path)
+        handle_txt("data", path)
+        assert os.path.exists(path)
+
+
+# ---------------------------------------------------------------------------
+# handle_png
+# ---------------------------------------------------------------------------
+
+class TestHandlePng:
+    def test_saves_image_to_file(self, tmp_path):
+        from spritegrid.main import handle_png
+        path = str(tmp_path / "out.png")
+        img = Image.new("RGB", (4, 4), (100, 200, 50))
+        handle_png(img, path)
+        assert os.path.exists(path)
+        loaded = Image.open(path)
+        assert loaded.size == (4, 4)
+
+    def test_prints_success_message(self, tmp_path, capsys):
+        from spritegrid.main import handle_png
+        path = str(tmp_path / "out.png")
+        handle_png(Image.new("RGB", (2, 2)), path)
+        out = capsys.readouterr().out
+        assert "Success" in out or "success" in out.lower() or str(path) in out
+
+    def test_invalid_path_does_not_raise(self, capsys):
+        from spritegrid.main import handle_png
+        img = Image.new("RGB", (2, 2))
+        # Non-existent directory → IOError caught
+        handle_png(img, "/nonexistent/dir/out.png")
+        err = capsys.readouterr().err
+        assert "Error" in err
+
+
+# ---------------------------------------------------------------------------
+# create_downsampled_image
+# ---------------------------------------------------------------------------
+
+class TestCreateDownsampledImage:
+    def _checkerboard(self, grid_w, grid_h, cells_w, cells_h):
+        """Create a simple test image with grid_w*cells_w × grid_h*cells_h pixels."""
+        w = grid_w * cells_w
+        h = grid_h * cells_h
+        arr = np.zeros((h, w, 3), dtype=np.uint8)
+        return Image.fromarray(arr, "RGB")
+
+    def test_output_size_matches_num_cells(self):
+        from spritegrid.main import create_downsampled_image
+        img = self._checkerboard(4, 4, 3, 2)
+        result = create_downsampled_image(img, 4, 4, 3, 2, kernel_size=(1, 1))
+        assert result.size == (3, 2)
+
+    def test_even_kernel_raises_value_error(self):
+        from spritegrid.main import create_downsampled_image
+        img = self._checkerboard(4, 4, 3, 3)
+        with pytest.raises(ValueError, match="odd"):
+            create_downsampled_image(img, 4, 4, 3, 3, kernel_size=(2, 3))
+
+    def test_kernel_larger_than_grid_raises(self):
+        from spritegrid.main import create_downsampled_image
+        img = self._checkerboard(3, 3, 2, 2)
+        with pytest.raises(ValueError, match="[Kk]ernel"):
+            create_downsampled_image(img, 3, 3, 2, 2, kernel_size=(5, 5))
+
+    def test_zero_grid_width_raises(self):
+        from spritegrid.main import create_downsampled_image
+        img = self._checkerboard(4, 4, 2, 2)
+        with pytest.raises(ValueError):
+            create_downsampled_image(img, 0, 4, 2, 2, kernel_size=(1, 1))
+
+    def test_returns_pil_image(self):
+        from spritegrid.main import create_downsampled_image
+        img = self._checkerboard(4, 4, 4, 4)
+        result = create_downsampled_image(img, 4, 4, 4, 4, kernel_size=(1, 1))
+        assert isinstance(result, Image.Image)
+
+    def test_geometric_median_type(self):
+        from spritegrid.main import create_downsampled_image
+        img = self._checkerboard(4, 4, 3, 3)
+        # Should not raise with median_type="geometric"
+        result = create_downsampled_image(img, 4, 4, 3, 3, kernel_size=(1, 1), median_type="geometric")
+        assert result.size == (3, 3)