Update README.md

README.md

@@ -21,21 +21,23 @@ Disparity maps for stereo matching, generated from the [Stereo4D](https://github
 ```
 data/train/
   metadata.csv
-  disparity/
-    0000000/
-      {vid_id}_frame_{frame_idx:06d}.png
-    0000001/
-      ...
+  0000000.zip   (first 50,000 images)
+  0000001.zip   (next 50,000 images)
+  ...
+  0000025.zip
 ```
 
-- **Disparity images**: 16-bit 784×784 PNG files storing per-pixel disparity values. You can read by following: https://github.com/NVlabs/FoundationStereo/blob/master/scripts/vis_dataset.py
-- **metadata.csv**: Links each disparity image back to its source YouTube video.
+Each zip contains disparity PNG files named `{vid_id}_frame_{frame_idx:06d}.png`.
+
+- **Disparity images**: 3-channel uint8 784×784 PNG files encoding per-pixel disparity. Decode with: `disp = (R * 255*255 + G * 255 + B) / 1000.0`. See also: https://github.com/NVlabs/FoundationStereo/blob/master/scripts/vis_dataset.py
+- **metadata.csv**: Links each disparity image back to its source YouTube video, with a `zip_file` column indicating which zip contains the image.
 
 ### Metadata Columns
 
 | Column | Description |
 |---|---|
-| `file_name` | Relative path to the disparity image |
+| `file_name` | Disparity image filename (inside the zip) |
+| `zip_file` | Which zip file contains this image |
 | `vid_id` | Clip identifier (matches the `.npz` calibration file) |
 | `frame_idx` | Frame index in the rectified stereo output |
 | `youtube_video_id` | YouTube video ID of the source 360 video |
@@ -60,17 +62,28 @@ This dataset contains **disparity maps only**. Due to the copyrights of these vi
 
 ### Camera Parameters
 
-The following assumed parameters are used for depth and normal map computation:
+The rectified stereo pairs are generated at 1024×1024 with the following pinhole camera model:
 
-| Parameter | Value | Notes |
-|---|---|---|
-| Baseline | 0.063 m | From Stereo4D calibration, the assumed interpupillary distance for the VR180 cameras. |
-| HFOV | 60° | Matches `output_hfov` in rectification |
-| fx, fy | ~678.8 px | `width / (2 * tan(HFOV/2))`, for 784×784 |
-| cx, cy | 392 px | Image center |
+| Parameter | Value (1024×1024 rectified) | Value (784×784 disparity) | Formula |
+|---|---|---|---|
+| HFOV | 60° | 60° | `output_hfov` in `batch_rectify.py` |
+| Baseline | 0.063 m | 0.063 m | Assumed interpupillary distance for VR180 cameras |
+| fx, fy | 886.8 px | 678.8 px | `size * 0.5 / tan(0.5 * HFOV * pi/180)` |
+| cx, cy | 512 px | 392 px | Image center |
 
 Depth is derived as: `depth = fx * baseline / disparity`.
 
+Since disparity is computed at 784×784 resolution (scale factor 784/1024 = 0.765625 of the 1024×1024 input), use the 784×784 camera parameters when converting disparity to depth:
+
+```python
+import numpy as np
+hfov = 60  # degrees
+baseline = 0.063  # meters
+imw = 784
+fx = imw * 0.5 / np.tan(0.5 * np.radians(hfov))  # 678.8 px
+depth = fx * baseline / disparity
+```
+
 
 ## Citation