fix: Improve transparency handling and optimization levels

- Handle transparency in whitespace trimming
- Use IntEnum for optimization levels
- Add proper level comparisons
- Treat transparent pixels as white for boundary detection
- Preserve transparency in output
- Fix black artifacts in transparent areas

settings.py

@@ -2,6 +2,19 @@
 
 import os
 import multiprocessing
+from enum import IntEnum
+
+class OptimizationLevel(IntEnum):
+    """Optimization levels for image processing.
+    
+    Levels:
+        1: Only trim whitespace
+        2: Trim + convert to 1-bit monochrome
+        3: All optimizations + optipng
+    """
+    TRIM = 1  # Only trim whitespace
+    MONOCHROME = 2  # Trim + convert to 1-bit monochrome
+    FULL = 3  # All optimizations + optipng
 
 # Number of parallel processes to use for operations that support parallelization
 # Defaults to number of CPU cores - 1, but never less than 1
@@ -14,5 +27,8 @@ PARALLEL_PROCESSES = int(os.getenv('NOTES_CLEANER_PARALLEL_PROCESSES', DEFAULT_P
 OPTIPNG_OPTIMIZATION_LEVEL = int(os.getenv('NOTES_CLEANER_OPTIPNG_LEVEL', '7'))  # 0-7, higher = better compression but slower
 TRIM_PADDING_PIXELS = int(os.getenv('NOTES_CLEANER_TRIM_PADDING', '20'))  # Padding around content after trimming
 
+# Image processing settings
+MONOCHROME_THRESHOLD = int(os.getenv('NOTES_CLEANER_MONO_THRESHOLD', '200'))  # 0-255, higher = more white
+
 # Temporary directory settings
 TEMP_DIR_PREFIX = 'notes_cleaner_'