fix: correct binary mask encoding - pink pixels get alpha=0 so 255-alpha becomes white (255) for removal

api/main.py

@@ -329,21 +329,25 @@ def inpaint_multipart(
             Image.fromarray(result).save(result_path, "PNG", optimize=False, compress_level=1)
             return {"result": result_name, "error": "pink/magenta paint detection failed - very few pixels detected"}
         
-        # Create black/white mask: white = remove (pink areas), black = keep (everything else)
+        # Create binary mask: Pink pixels → white (255), Everything else → black (0)
+        # Encode in RGBA format for process_inpaint
+        # process_inpaint does: mask = 255 - mask[:,:,3]
+        # So: alpha=0 (transparent/pink) → becomes 255 (white/remove)
+        #     alpha=255 (opaque/keep) → becomes 0 (black/keep)
         mask_rgba = np.zeros((binmask.shape[0], binmask.shape[1], 4), dtype=np.uint8)
-        mask_rgba[:, :, 0] = binmask  # R: white where pink detected
-        mask_rgba[:, :, 1] = binmask  # G: white where pink detected
-        mask_rgba[:, :, 2] = binmask  # B: white where pink detected
-        mask_rgba[:, :, 3] = 255      # Alpha: fully opaque
+        mask_rgba[:, :, 0] = binmask  # R: white where pink (for visualization)
+        mask_rgba[:, :, 1] = binmask  # G: white where pink
+        mask_rgba[:, :, 2] = binmask  # B: white where pink
+        # Alpha: invert so pink areas get alpha=0 → will become white after 255-alpha
+        mask_rgba[:, :, 3] = 255 - binmask
         
-        log.info("Successfully created black/white mask: %d white pixels (to remove), %d black pixels (to keep)",
+        log.info("Successfully created binary mask: %d pink pixels → white (255), %d pixels → black (0)",
                  nonzero, binmask.shape[0] * binmask.shape[1] - nonzero)
     else:
         mask_rgba = _load_rgba_mask_from_image(m)
 
-    # When mask_is_painted=true, we create white=remove masks, so invert_mask should be False
-    # (white pixels should stay white to indicate removal)
-    actual_invert = invert_mask if not mask_is_painted else False
+    # When mask_is_painted=true, we encode pink as alpha=0, so process_inpaint's default invert_mask=True works correctly
+    actual_invert = invert_mask  # Use default True for painted masks
     log.info("Using invert_mask=%s (mask_is_painted=%s)", actual_invert, mask_is_painted)
     
     result = process_inpaint(np.array(img), mask_rgba, invert_mask=actual_invert)
@@ -423,20 +427,25 @@ def remove_pink_segments(
             "error": "No pink/magenta segments detected. Please paint areas to remove with magenta/pink color (RGB 255,0,255)."
         }
     
-    # Create mask: 
-    # - White = pink areas (remove)
-    # - Black = everything else (keep) - automatically, no black painting needed
+    # Create binary mask: Pink pixels → white (255), Everything else → black (0)
+    # But we need to encode it in RGBA format that process_inpaint expects
+    # process_inpaint does: mask = 255 - mask[:,:,3]
+    # So: alpha=0 (transparent/pink) → becomes 255 (white/remove)
+    #     alpha=255 (opaque/keep) → becomes 0 (black/keep)
     mask_rgba = np.zeros((binmask.shape[0], binmask.shape[1], 4), dtype=np.uint8)
-    mask_rgba[:, :, 0] = binmask  # R: white where pink detected
-    mask_rgba[:, :, 1] = binmask  # G: white where pink detected
-    mask_rgba[:, :, 2] = binmask  # B: white where pink detected
-    mask_rgba[:, :, 3] = 255      # Alpha: fully opaque
+    # RGB channels don't matter for process_inpaint, but set them to white where pink for visualization
+    mask_rgba[:, :, 0] = binmask  # R: white where pink
+    mask_rgba[:, :, 1] = binmask  # G: white where pink  
+    mask_rgba[:, :, 2] = binmask  # B: white where pink
+    # Alpha: 0 (transparent) where pink → will become white after 255-alpha
+    #        255 (opaque) everywhere else → will become black after 255-alpha
+    mask_rgba[:, :, 3] = 255 - binmask  # Invert: pink areas get alpha=0, rest get alpha=255
     
     total_pixels = binmask.shape[0] * binmask.shape[1]
-    log.info(f"Created mask: {nonzero} white pixels (remove/pink), {total_pixels - nonzero} black pixels (keep - everything else automatically)")
+    log.info(f"Created binary mask: {nonzero} pink pixels → white (255) in final mask, {total_pixels - nonzero} black (0) - everything else automatically")
     
-    # Process with invert_mask=False because white pixels = remove (standard)
-    result = process_inpaint(np.array(img), mask_rgba, invert_mask=False)
+    # Process with invert_mask=True (default) because process_inpaint expects alpha=0 for removal
+    result = process_inpaint(np.array(img), mask_rgba, invert_mask=True)
     result_name = f"output_{uuid.uuid4().hex}.png"
     result_path = os.path.join(OUTPUT_DIR, result_name)
     Image.fromarray(result).save(result_path, "PNG", optimize=False, compress_level=1)