TST: Add 4-bit test image (#3761)

Author: adityamoolya

tests/example_files.yaml

@@ -104,6 +104,8 @@
   url: https://github.com/py-pdf/pypdf/assets/4083478/56c93021-33cd-4387-ae13-5cbe7e673f42
 - local_filename: paid.pdf
   url: https://github.com/py-pdf/pypdf/files/12050253/tt.pdf
+- local_filename: 4bits_image.pdf
+  url: https://github.com/user-attachments/files/27491104/test_4bit.pdf
 - local_filename: Pesquisa-de-Precos-Combustiveis-novembro-2023.pdf
   url: https://www.joinville.sc.gov.br/wp-content/uploads/2023/11/Pesquisa-de-Precos-Combustiveis-novembro-2023.pdf
 - local_filename: iss2138.pdf

tests/test_filters.py

@@ -485,7 +485,7 @@ def test_index_lookup():
 
 @pytest.mark.enable_socket
 def test_2bits_image():
-    """From #1954, test with 2bits image. TODO: 4bits also"""
+    """From #1954, test with 2bits image."""
     reader = PdfReader(BytesIO(get_data_from_url(name="paid.pdf")))
     url_png = "https://user-images.githubusercontent.com/4083478/253568117-ca95cc85-9dea-4145-a5e0-032f1c1aa322.png"
     name_png = "Paid.png"
@@ -494,6 +494,17 @@ def test_2bits_image():
     assert image_similarity(data.image, refimg) > 0.99
 
 
+@pytest.mark.enable_socket
+def test_4bits_image():
+    """From #1954, test with 4bits image."""
+    reader = PdfReader(BytesIO(get_data_from_url(name="4bits_image.pdf")))
+    url_png = "https://github.com/user-attachments/files/27492549/4bits_image.png.txt"
+    name_png = "4bits_image.png"
+    refimg = BytesIO(get_data_from_url(url=url_png, name=name_png))
+    data = reader.pages[0].images[0]
+    assert image_similarity(data.image, refimg) > 0.99
+
+
 @pytest.mark.enable_socket
 def test_gray_devicen_cmyk():
     """