feat: add PNG support to optimize-images hook

.pre-commit-hooks.yaml

@@ -11,6 +11,6 @@
   name: Optimize Images
   entry: optimize-images
   language: python
-  types_or: [jpeg]
-  description: Resize and compress JPEG images to reduce repository size.
+  types_or: [jpeg, png]
+  description: Resize and compress JPEG and PNG images to reduce repository size.
   stages: [pre-commit, pre-merge-commit, pre-push, manual]

README.md

@@ -11,7 +11,7 @@ Two hooks for OpenSCAD-based 3D printing projects:
 | Hook | Description |
 |------|-------------|
 | `flatten-validate` | Runs `scadm flatten --all` and fails if flattened files have uncommitted changes |
-| `optimize-images` | Resizes oversized JPEGs, compresses them, and strips EXIF data (privacy) |
+| `optimize-images` | Resizes oversized JPEGs/PNGs, compresses them, and strips metadata (privacy) |
 
 ## 🔧 Usage
 
@@ -44,7 +44,7 @@ Flattens OpenSCAD files via [scadm](https://pypi.org/project/scadm/) and validat
 
 ### `optimize-images`
 
-Resizes JPEGs exceeding max width, compresses to target quality, and strips EXIF metadata (removes GPS coordinates from real-life photos).
+Resizes JPEGs and PNGs exceeding max width, compresses them, and strips metadata. EXIF data (including GPS coordinates) is removed from JPEGs; text metadata chunks are removed from PNGs.
 
 ```yaml
 - id: optimize-images
@@ -56,7 +56,7 @@ Resizes JPEGs exceeding max width, compresses to target quality, and strips EXIF
 | Arg | Default | Description |
 |-----|---------|-------------|
 | `--max-width` | `1920` | Maximum image width in pixels |
-| `--quality` | `85` | JPEG compression quality (1-95) |
+| `--quality` | `85` | JPEG compression quality (1-95, ignored for PNG) |
 
 Both hooks **fail when files are modified**, printing instructions to `git add` the changes. Re-run `git commit` after staging.
 

src/pre_commit_hooks/optimize_images.py

@@ -1,4 +1,4 @@
-"""Pre-commit hook: resize and compress JPEG images."""
+"""Pre-commit hook: resize and compress JPEG and PNG images."""
 
 import argparse
 import shlex
@@ -8,24 +8,32 @@
 
 
 def _optimize_file(filepath, max_width, quality):
-    """Resize, compress, and strip EXIF from a single JPEG file.
+    """Resize, compress, and strip metadata from a single image file.
+
+    Supports JPEG and PNG formats. JPEGs are compressed with the given quality
+    and have EXIF data stripped. PNGs are saved with Pillow's optimize flag
+    and have text metadata stripped.
 
     Args:
-        filepath: Path to the JPEG file.
+        filepath: Path to the image file.
         max_width: Maximum allowed width in pixels.
-        quality: JPEG compression quality (1-95).
+        quality: JPEG compression quality (1-95). Ignored for PNG.
 
     Returns:
         True if the file was modified, False otherwise.
     """
     with Image.open(filepath) as img:
-        # Apply EXIF orientation before checking size
+        img_format = img.format  # "JPEG" or "PNG"
+        if img_format not in ("JPEG", "PNG"):
+            msg = f"Unsupported format '{img_format}' for {filepath}"
+            raise ValueError(msg)
+        has_png_text = img_format == "PNG" and bool(getattr(img, "text", None))
         img = ImageOps.exif_transpose(img)
         width, height = img.size
         needs_resize = width > max_width
         has_exif = bool(img.info.get("exif"))
 
-        if not needs_resize and not has_exif:
+        if not needs_resize and not has_exif and not has_png_text:
             return False
 
         if needs_resize:
@@ -34,17 +42,28 @@ def _optimize_file(filepath, max_width, quality):
             new_size = (max_width, new_height)
             img = img.resize(new_size, Image.LANCZOS)
 
-        if img.mode in ("RGBA", "P"):
-            img = img.convert("RGB")
-        img.save(filepath, "JPEG", quality=quality, optimize=True)
+        if img_format == "PNG":
+            # Strip metadata by creating a clean image without materializing
+            # the pixel stream as a Python list.
+            clean = Image.new(img.mode, img.size)
+            if img.mode == "P":
+                palette = img.getpalette()
+                if palette is not None:
+                    clean.putpalette(palette)
+            clean.frombytes(img.tobytes())
+            clean.save(filepath, "PNG", optimize=True)
+        else:
+            if img.mode in ("RGBA", "P"):
+                img = img.convert("RGB")
+            img.save(filepath, "JPEG", quality=quality, optimize=True)
 
     return True
 
 
 def main():
     """Entry point for the optimize-images pre-commit hook."""
-    parser = argparse.ArgumentParser(description="Resize and compress JPEG images.")
-    parser.add_argument("filenames", nargs="*", help="JPEG files to check.")
+    parser = argparse.ArgumentParser(description="Resize and compress images.")
+    parser.add_argument("filenames", nargs="*", help="Image files to check.")
     parser.add_argument(
         "--max-width",
         type=int,

tests/test_optimize_images.py

@@ -3,6 +3,7 @@
 from unittest import mock
 
 from PIL import Image
+from PIL.PngImagePlugin import PngInfo
 
 from pre_commit_hooks.optimize_images import main
 
@@ -27,6 +28,23 @@ def _create_jpeg(path, width, height, exif=False):
         img.save(str(path), "JPEG", quality=95)
 
 
+def _create_png(path, width, height, text_meta=False):
+    """Create a test PNG file.
+
+    Args:
+        path: File path to write.
+        width: Image width in pixels.
+        height: Image height in pixels.
+        text_meta: If True, embed text metadata chunks.
+    """
+    img = Image.new("RGBA", (width, height), color="blue")
+    pnginfo = PngInfo()
+    if text_meta:
+        pnginfo.add_text("Software", "TestSuite")
+        pnginfo.add_text("Comment", "test metadata")
+    img.save(str(path), "PNG", pnginfo=pnginfo)
+
+
 class TestOptimizeImages:
     """Tests for the optimize-images hook."""
 
@@ -130,3 +148,116 @@ def test_error_causes_failure(self, tmp_path):
             result = main()
 
         assert result == 1
+
+    # --- PNG tests ---
+
+    def test_large_png_resized(self, tmp_path):
+        """PNGs wider than max-width are resized."""
+        img_path = tmp_path / "large.png"
+        _create_png(img_path, 3000, 2000)
+
+        with mock.patch("sys.argv", ["optimize-images", "--max-width=1920", str(img_path)]):
+            result = main()
+
+        assert result == 1
+        with Image.open(img_path) as img:
+            assert img.size[0] == 1920
+            assert img.size[1] == 1280
+
+    def test_small_png_untouched(self, tmp_path):
+        """Small PNGs without metadata are not modified."""
+        img_path = tmp_path / "small.png"
+        _create_png(img_path, 800, 600)
+        original_size = img_path.stat().st_size
+
+        with mock.patch("sys.argv", ["optimize-images", "--max-width=1920", str(img_path)]):
+            result = main()
+
+        assert result == 0
+        assert img_path.stat().st_size == original_size
+
+    def test_png_metadata_stripped(self, tmp_path):
+        """Text metadata is stripped from PNGs."""
+        img_path = tmp_path / "meta.png"
+        _create_png(img_path, 800, 600, text_meta=True)
+
+        with mock.patch("sys.argv", ["optimize-images", "--max-width=1920", str(img_path)]):
+            result = main()
+
+        assert result == 1
+        with Image.open(img_path) as img:
+            assert not getattr(img, "text", None)
+
+    def test_png_preserves_transparency(self, tmp_path):
+        """PNGs retain their alpha channel after optimization."""
+        img_path = tmp_path / "alpha.png"
+        img = Image.new("RGBA", (3000, 2000), color=(0, 0, 255, 128))
+        img.save(str(img_path), "PNG")
+
+        with mock.patch("sys.argv", ["optimize-images", "--max-width=1920", str(img_path)]):
+            result = main()
+
+        assert result == 1
+        with Image.open(img_path) as img:
+            assert img.mode == "RGBA"
+            assert img.size[0] == 1920
+
+    def test_mixed_jpeg_and_png(self, tmp_path):
+        """Both JPEG and PNG files are handled in a single run."""
+        jpg_path = tmp_path / "big.jpg"
+        png_path = tmp_path / "big.png"
+        _create_jpeg(jpg_path, 4000, 3000)
+        _create_png(png_path, 4000, 3000)
+
+        with mock.patch(
+            "sys.argv",
+            ["optimize-images", "--max-width=1920", str(jpg_path), str(png_path)],
+        ):
+            result = main()
+
+        assert result == 1
+        with Image.open(jpg_path) as img:
+            assert img.size[0] == 1920
+        with Image.open(png_path) as img:
+            assert img.size[0] == 1920
+
+    def test_paletted_png_resized(self, tmp_path):
+        """Paletted PNGs are resized and palette is preserved."""
+        img_path = tmp_path / "palette.png"
+        img = Image.new("P", (3000, 2000))
+        img.putpalette([i % 256 for i in range(768)])
+        img.save(str(img_path), "PNG")
+
+        with mock.patch("sys.argv", ["optimize-images", "--max-width=1920", str(img_path)]):
+            result = main()
+
+        assert result == 1
+        with Image.open(img_path) as img:
+            assert img.mode == "P"
+            assert img.size[0] == 1920
+            assert img.getpalette() is not None
+
+    def test_paletted_png_with_transparency(self, tmp_path):
+        """Paletted PNGs with transparency are handled correctly."""
+        img_path = tmp_path / "palette_alpha.png"
+        img = Image.new("RGBA", (3000, 2000), color=(255, 0, 0, 128))
+        img = img.convert("P")
+        img.save(str(img_path), "PNG")
+
+        with mock.patch("sys.argv", ["optimize-images", "--max-width=1920", str(img_path)]):
+            result = main()
+
+        assert result == 1
+        with Image.open(img_path) as img:
+            assert img.size[0] == 1920
+
+    def test_unsupported_format_raises(self, tmp_path):
+        """Unsupported image formats cause a failure."""
+        img_path = tmp_path / "image.bmp"
+        img = Image.new("RGB", (800, 600), color="green")
+        img.save(str(img_path), "BMP")
+
+        with mock.patch("sys.argv", ["optimize-images", str(img_path)]):
+            result = main()
+
+        assert result == 1