Report blank YOLO label QA tiles

scripts/render_operator_yolo_label_qa_contact_sheets.py

@@ -31,6 +31,12 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument("--max-tiles", type=int, default=24, help="Maximum selected tiles to render")
     parser.add_argument("--columns", type=int, default=4, help="Contact-sheet columns")
     parser.add_argument("--thumb-size", type=int, default=256, help="Rendered tile thumbnail size in pixels")
+    parser.add_argument(
+        "--blank-range-threshold",
+        type=int,
+        default=3,
+        help="Mark rendered images with grayscale max-min range at or below this value as low variance.",
+    )
     return parser.parse_args()
 
 
@@ -146,6 +152,7 @@ def draw_tile_card(
     thumb_size: int,
     invalid_label_count: int,
     missing_label_file: bool,
+    low_visual_variance: bool,
 ) -> Image.Image:
     header_height = 44
     card = Image.new("RGB", (thumb_size, thumb_size + header_height), color=(245, 247, 250))
@@ -163,6 +170,8 @@ def draw_tile_card(
         subtitle_parts.append("missing-label-file")
     if invalid_label_count:
         subtitle_parts.append(f"invalid:{invalid_label_count}")
+    if low_visual_variance:
+        subtitle_parts.append("low-variance")
     draw.text((6, 6), title[:44], fill=(255, 255, 255), font=font)
     draw.text((6, 24), " | ".join(subtitle_parts)[:52], fill=(191, 219, 254), font=font)
 
@@ -180,6 +189,12 @@ def draw_tile_card(
     return card
 
 
+def image_has_low_visual_variance(image_path: Path, blank_range_threshold: int) -> bool:
+    image = Image.open(image_path).convert("L")
+    min_value, max_value = image.getextrema()
+    return (max_value - min_value) <= blank_range_threshold
+
+
 def build_contact_sheet(cards: list[Image.Image], columns: int, output_path: Path) -> None:
     if not cards:
         return
@@ -216,6 +231,7 @@ def build_report(summary: dict[str, Any], summary_path: Path, args: argparse.Nam
     missing_label_file_count = 0
     invalid_label_count = 0
     valid_label_count = 0
+    low_visual_variance_tile_count = 0
 
     for tile in selected_tiles:
         image_path = resolve_path(tile.get("image_path"), summary_path)
@@ -227,9 +243,13 @@ def build_report(summary: dict[str, Any], summary_path: Path, args: argparse.Nam
             missing_label_file_count += 1
 
         rendered = False
+        low_visual_variance = False
         if image_path is None or not image_path.exists():
             missing_image_count += 1
         else:
+            low_visual_variance = image_has_low_visual_variance(image_path, args.blank_range_threshold)
+            if low_visual_variance:
+                low_visual_variance_tile_count += 1
             rendered_cards.append(
                 draw_tile_card(
                     image_path=image_path,
@@ -238,6 +258,7 @@ def build_report(summary: dict[str, Any], summary_path: Path, args: argparse.Nam
                     thumb_size=args.thumb_size,
                     invalid_label_count=tile_invalid_count,
                     missing_label_file=missing_label_file,
+                    low_visual_variance=low_visual_variance,
                 )
             )
             rendered = True
@@ -255,6 +276,7 @@ def build_report(summary: dict[str, Any], summary_path: Path, args: argparse.Nam
                 "valid_label_count": len(boxes),
                 "invalid_label_count": tile_invalid_count,
                 "missing_label_file": missing_label_file,
+                "low_visual_variance": low_visual_variance,
                 "rendered": rendered,
             }
         )
@@ -285,6 +307,8 @@ def build_report(summary: dict[str, Any], summary_path: Path, args: argparse.Nam
             "missing_label_file_count": missing_label_file_count,
             "invalid_label_count": invalid_label_count,
             "valid_label_count": valid_label_count,
+            "low_visual_variance_tile_count": low_visual_variance_tile_count,
+            "blank_range_threshold": args.blank_range_threshold,
             "contact_sheets": contact_sheets,
             "selected_tiles": selected_report_tiles,
         },
@@ -302,6 +326,7 @@ def write_markdown(report: dict[str, Any], output_dir: Path) -> None:
         f"- missing images: {report['missing_image_count']}",
         f"- missing label files: {report['missing_label_file_count']}",
         f"- invalid label rows: {report['invalid_label_count']}",
+        f"- low-variance rendered tiles: {report['low_visual_variance_tile_count']}",
         f"- valid labels rendered: {report['valid_label_count']}",
         "",
         "## Contact Sheets",
@@ -323,6 +348,8 @@ def write_markdown(report: dict[str, Any], output_dir: Path) -> None:
             flags.append("missing-label-file")
         if tile["invalid_label_count"]:
             flags.append(f"invalid:{tile['invalid_label_count']}")
+        if tile["low_visual_variance"]:
+            flags.append("low-variance")
         flag_text = ", ".join(flags) if flags else "ok"
         lines.append(
             "- "