Backport of https://github.com/lincolnloop/python-qrcode/pull/338

diff --git a/qrcode/main.py b/qrcode/main.py
index 0ac91bb..53f2ab2 100644
--- a/qrcode/main.py
+++ b/qrcode/main.py
@@ -16,7 +16,6 @@ from typing_extensions import Literal
 
 from qrcode import constants, exceptions, util
 from qrcode.image.base import BaseImage
-from qrcode.image.pure import PyPNGImage
 
 ModulesType = List[List[Optional[bool]]]
 # Cache modules generated just based on the QR Code version
@@ -360,7 +359,11 @@ class QRCode(Generic[GenericImage]):
                 from qrcode.image.pil import Image, PilImage
 
                 # Use PIL by default if available, otherwise use PyPNG.
-                image_factory = PilImage if Image else PyPNGImage
+                if Image is not None:
+                    image_factory = PilImage
+                else:
+                    from qrcode.image.pure import PyPNGImage
+                    image_factory = PyPNGImage
 
         im = image_factory(
             self.border,
diff --git a/qrcode/tests/test_qrcode.py b/qrcode/tests/test_qrcode.py
index 5c1ea35..24c36f8 100644
--- a/qrcode/tests/test_qrcode.py
+++ b/qrcode/tests/test_qrcode.py
@@ -5,18 +5,21 @@ import warnings
 from tempfile import mkdtemp
 from unittest import mock
 
-import png
-
 import qrcode
 import qrcode.util
 from qrcode.compat.pil import Image as pil_Image
 from qrcode.exceptions import DataOverflowError
 from qrcode.image.base import BaseImage
-from qrcode.image.pure import PyPNGImage
 from qrcode.image.styledpil import StyledPilImage
 from qrcode.image.styles import colormasks, moduledrawers
 from qrcode.util import MODE_8BIT_BYTE, MODE_ALPHA_NUM, MODE_NUMBER, QRData
 
+try:
+    import png
+    from qrcode.image.pure import PyPNGImage
+except ImportError:
+    PyPNGImage = None
+
 UNICODE_TEXT = "\u03b1\u03b2\u03b3"
 WHITE = (255, 255, 255)
 BLACK = (0, 0, 0)
@@ -175,6 +178,7 @@ class QRCodeTests(unittest.TestCase):
         self.assertTrue(MockFactory.new_image.called)
         self.assertTrue(MockFactory.drawrect.called)
 
+    @unittest.skipIf(not PyPNGImage, "Requires pypng")
     def test_render_pypng(self):
         qr = qrcode.QRCode()
         qr.add_data(UNICODE_TEXT)
@@ -184,6 +188,7 @@ class QRCodeTests(unittest.TestCase):
         print(img.width, img.box_size, img.border)
         img.save(io.BytesIO())
 
+    @unittest.skipIf(not PyPNGImage, "Requires pypng")
     def test_render_pypng_to_str(self):
         qr = qrcode.QRCode()
         qr.add_data(UNICODE_TEXT)
diff --git a/setup.cfg b/setup.cfg
index 3aff842..c17189b 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -30,7 +30,6 @@ packages = find:
 install_requires = 
 	colorama;platform_system=="Windows"
 	typing_extensions
-	pypng
 python_requires = >= 3.7
 
 [options.extras_require]
@@ -45,6 +44,8 @@ test =
 	pytest
 pil = 
 	pillow>=9.1.0
+png = 
+	pypng
 all = 
 	zest.releaser[recommended]
 	tox