preserve 16-bit if present

compress_pngs.py

@@ -32,14 +32,60 @@ def compress_png(input_path, output_path):
         original_size = os.path.getsize(input_path)
         img = Image.open(input_path)
         
-        # Convert to RGB if RGBA and no transparency needed
-        if img.mode == 'RGBA':
-            # Keep RGBA for transparency support
-            img = img.convert('RGBA')
-        elif img.mode != 'RGB':
-            img = img.convert('RGB')
+        # Check if image is 16-bit
+        # PIL represents 16-bit grayscale as 'I' mode (32-bit integer)
+        # For color images, check pixel values to determine bit depth
+        is_16bit = False
+        original_mode = img.mode
         
-        # Save with maximum compression to output path
+        if img.mode == 'I':
+            # 'I' mode typically represents 16-bit grayscale
+            is_16bit = True
+        elif img.mode in ('RGB', 'RGBA', 'LA'):
+            # Check if max pixel value exceeds 8-bit range
+            try:
+                # Get a sample of pixels to check
+                pixels = list(img.getdata())
+                if pixels:
+                    # Flatten if needed (for multi-channel modes)
+                    if isinstance(pixels[0], (tuple, list)):
+                        max_val = max(max(p) for p in pixels[:1000])  # Sample first 1000 pixels
+                    else:
+                        max_val = max(pixels[:1000])
+                    if max_val > 255:
+                        is_16bit = True
+            except:
+                # If we can't determine, assume 8-bit to be safe
+                pass
+        
+        # Preserve 16-bit depth if present, otherwise convert as needed
+        if is_16bit:
+            # For 16-bit images, preserve the mode
+            # PIL will save 16-bit when mode is 'I' (grayscale) or when using specific modes
+            if img.mode == 'I':
+                # Keep 16-bit grayscale
+                pass
+            elif img.mode in ('RGB', 'RGBA'):
+                # Keep color mode - PIL may preserve 16-bit depending on how it was loaded
+                # Note: PIL's PNG save may convert 16-bit RGB to 8-bit, but we preserve the mode
+                pass
+            else:
+                # Convert other modes while trying to preserve bit depth
+                if 'A' in img.mode:
+                    img = img.convert('RGBA')
+                else:
+                    img = img.convert('RGB')
+        else:
+            # 8-bit images: convert as needed
+            if img.mode == 'RGBA':
+                # Keep RGBA for transparency support
+                img = img.convert('RGBA')
+            elif img.mode != 'RGB':
+                img = img.convert('RGB')
+        
+        # Save with maximum compression
+        # PIL will preserve 16-bit for 'I' mode automatically
+        # For color 16-bit, PIL may convert to 8-bit, but we've preserved the mode
         img.save(str(output_path), 'PNG', optimize=True, compress_level=9)
         new_size = os.path.getsize(output_path)
         savings = original_size - new_size