Update README.md

The file description of the image segmentation folder has been updated

README.md

@@ -158,4 +158,28 @@ These files provide **low-level driving signals, ego vehicle states, and scene-l
 - `Tester*_IS/` (instance segmentation outputs)
 
 
+### `Tester*_IS/Tester*_<scene_id>_IS/`
+
+This directory contains **instance segmentation (IS) outputs** for each scene, generated using **CARLA 0.9.15**.
+
+Each subfolder corresponds to one scene and includes the following files:
+##### `frame_output/`
+- A sequence of **PNG images** representing **instance segmentation foregrounds**
+- Each image corresponds to **one frame**, and is **row-aligned** with the CSV files in other modalities
+- This design enables precise **frame-level alignment and multimodal analysis**
+
+##### `obj_pixel_table.csv`
+- A lookup table mapping **vehicle IDs to instance segmentation pixel values**
+- Required because in **CARLA 0.9.15**, instance segmentation assigns **random pixel values** to objects in each run
+- This file provides the **ground-truth correspondence** between vehicles and their pixel labels **for this specific scene**
+
+##### `processed_screenshot.png`
+- A **top-down overview image** captured at the **start of the takeover recording**
+- Visualizes the **vehicle–pixel correspondence**, where connecting lines indicate matched vehicles and pixel labels
+- This file is intended **for validation and debugging only**
+
+**Important note:**  
+If abnormal vertical lines or incorrect non-motorized object segmentation are observed in `processed_screenshot.png`, the data in this folder **should not be used**, as it indicates unreliable instance segmentation results for the scene.
+
+Together, these files support **pixel-level, object-aware analysis** of driver attention and scene context, and are designed to be used jointly with gaze annotations and feature CSV files.