Update README.md

README.md

@@ -12,21 +12,99 @@ license: mit
 
 # KTH HOG Features (NPZ)
 
-This repository hosts a precomputed HOG feature dataset derived from the KTH Human Action Recognition dataset, used by the CNN-for-HAR Streamlit demo.
+This repository hosts a precomputed HOG feature dataset derived from the KTH Human Action Recognition (KTH-HAR) videos. It is used by the CNN-for-HAR Streamlit demo and allows fast inference/training without decoding raw videos at runtime.
 
-The file contains:
-- `features`: shape `(N, T*3780)` float32
-- `bboxes`: shape `(N, T, 4)` float32
-- `labels`: shape `(N,)` int64
-- `metadata`: list of dicts with split/subject/action/video info
+## What this file contains
 
-## File
-- `hog_aug_4framegap.npz` — ~3GB
+`hog_aug_4framegap.npz` (~3GB) includes:
+
+- `features`: shape `(N, T*3780)` float32  
+- `bboxes`: shape `(N, T, 4)` float32, normalized `(cx, cy, w, h)` per frame  
+- `labels`: shape `(N,)` int64  
+- `metadata`: list of dicts with `video_key`, `subject`, `action`, `split`, `group_idx`, `aug_idx`, `aug_name`, `frame_indices`  
+- `config`: dict with generation settings (see below)
+
+Each sample is a clip of **T frames**, stored as a flattened HOG vector. HOG is computed on 64×128 crops (OpenCV HOG defaults), which yields **3780 features per frame**.
+
+---
+
+## How the file is generated (pipeline)
+
+This `.npz` is produced by `extract_hog_augmented.py` in the main repo:
+
+1. Load **bbox metadata JSON** (groups of frame indices per clip).
+2. For each video:
+   - Read only the needed frames.
+3. For each clip:
+   - **Always include the original version** (no augmentation).
+   - For **train clips only**, generate additional augmented versions (`num_aug - 1`).
+4. For every variant:
+   - Crop person bbox → resize to 64×128  
+   - Optional flip + photometric changes  
+   - Compute HOG  
+   - Save HOG + normalized bbox info  
+
+---
+
+## What `num_aug=4` means
+
+When `num_aug=4`, each **train clip** becomes **4 variants**:
+
+1. `orig` — no augmentation  
+2. `flip` — horizontal flip only  
+3. `jit0` — random jitter + photometric + possible blur/noise  
+4. `jit1` — another random jitter + photometric + possible blur/noise  
+
+Test clips always have **only the original version**.
+
+---
+
+## Augmentations used in `jit*`
+
+The `jit*` variants apply a random combination of:
+
+- **BBox jitter**: translation `(dx, dy)` + scale  
+- **Random flip** (50%)  
+- **Photometric changes**: contrast (`alpha`), brightness (`beta`)  
+- **Gamma**  
+- **Noise** (optional)  
+- **Blur** (optional)
+
+### `mild` profile (default)
+- scale: 0.92–1.08  
+- dx: ±5, dy: ±3  
+- alpha: 0.85–1.15  
+- beta: -15…+15  
+- gamma: 0.95–1.05  
+- noise: std 2.0 with p=0.5  
+- blur: p=0.15 (kernel 3)
+
+### `strong` profile
+- scale: 0.88–1.15  
+- dx: ±8, dy: ±6  
+- alpha: 0.75–1.25  
+- beta: -25…+25  
+- gamma: 0.85–1.15  
+- noise: std 4.0 with p=0.7  
+- blur: p=0.25 (kernel 3)
+
+---
+
+## What `frame_gap=4` means
+
+The **frame gap** is defined in the bbox JSON (not in the extractor).  
+Each clip groups frames spaced by a fixed gap (e.g., every 4th frame).  
+That’s why this file is named `hog_aug_4framegap.npz`.
+
+---
 
 ## Direct download
-- `https://huggingface.co/datasets/Mihai20/kth-hog-npz/resolve/main/hog_aug_4framegap.npz`
+- https://huggingface.co/datasets/Mihai20/kth-hog-npz/resolve/main/hog_aug_4framegap.npz
+
+---
 
 ## Example usage (Python)
+
 ```python
 import numpy as np
 
@@ -35,14 +113,10 @@ features = data["features"]
 bboxes = data["bboxes"]
 labels = data["labels"]
 metadata = data["metadata"].tolist()
+config = data["config"].item()  # contains num_aug, profile, etc.
 ```
 
 ## Notes
-This file is meant for inference and demo usage, not raw video processing.
-It can be used without the original videos.
-
-## License
-MIT (same as the main project).
-
-## Contact
-If you use this dataset, please cite or link the main project: https://github.com/Mihai20/CNN_for_HAR
+- Intended for inference + demo usage without raw video decoding.
+- The original videos are not required to use this .npz.
+- Augmentation settings are saved in config inside the file.