PointOfFocus

A lightweight Flask service that computes the most salient (attention-grabbing) point in an image using OpenCV’s Spectral Residual Saliency, and returns JSON:

{
  "focus": { "x": 1432, "y": 514 },
  "width": 1920,
  "height": 1080
}

It supports both remote images (via URL) and local files (via filesystem path), and ships with a Dockerfile for easy containerized deployment.

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Table of Contents

• Features

• Prerequisites

• Local Installation & Running

  • 1. Clone the Repo
  • 2. Create & Activate a Virtualenv
  • 3. Install Dependencies
  • 4. Run the App

• Docker Deployment

  • Build the Image
  • Run the Container

• API Usage

  • Endpoint
  • Parameters
  • Examples

• Project Structure

• Troubleshooting

• License

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Features

• Saliency-based focus detection using OpenCV contrib module
• Supports remote URLs or local paths
• Returns focus point and image dimensions as JSON
• Docker-ready for easy deployment
• Simple, zero-configuration HTTP API

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Prerequisites

• Python 3.8+ (tested on 3.12)
• Git (for cloning the repo)
• Docker (optional, for containerized deployment)

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Local Installation & Running

1. Clone the Repo

git clone https://your.git.host/flask-saliency-focus.git
cd flask-saliency-focus

2. Create & Activate a Virtualenv

# macOS/Linux
python3 -m venv venv
source venv/bin/activate

# Windows (PowerShell)
py -3 -m venv venv
.\venv\Scripts\Activate.ps1

3. Install Dependencies

pip install --upgrade pip
pip install -r requirements.txt

This will install:

• Flask
• opencv-contrib-python==4.5.5.64 (with saliency API)
• numpy<2.0
• requests

4. Run the App

export FLASK_APP=app.main
export FLASK_ENV=development        # enables debug mode (auto-reload, stack traces)
flask run --host=0.0.0.0 --port=5000

You should see:

 * Serving Flask app "app.main"
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

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Docker Deployment

If you prefer containerization, the included Dockerfile builds a minimal image with Gunicorn.

Build the Image

docker build -t saliency-focus .

Run the Container

docker run --rm -p 5000:5000 saliency-focus

Now the service is available at http://localhost:5000.

To test with a local file, bind your images directory:

docker run --rm -v $(pwd)/images:/data -p 5000:5000 saliency-focus

Then request:

curl "http://localhost:5000/focus?path=/data/image1.jpg"

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API Usage

Endpoint

GET /focus

Parameters

Name	Type	Required?	Description
url	string	either this or path	HTTP URL of an image to analyze.
path	string	either this or url	Filesystem path to a local image.

Examples

• Remote image

  curl "http://localhost:5000/focus?url=https://example.com/pic.jpg"

• Local file

  curl "http://localhost:5000/focus?path=image1.jpg

Success response (HTTP 200):

{
  "focus": { "x": 1432, "y": 514 },
  "width": 1920,
  "height": 1080
}

Error response (HTTP 4xx/5xx):

{ "error": "Could not load image at path: /invalid.jpg" }

---

Project Structure

flask-saliency-focus/
├── Dockerfile
├── requirements.txt
└── app
    ├── __init__.py           # makes `app` a Python package
    ├── main.py               # Flask app & routes
    └── saliency.py           # image loading & saliency logic

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Troubleshooting

• ImportError: cv2 has no attribute saliency Make sure you installed opencv-contrib-python, not just opencv-python, and that it’s pinned to a compatible version:

  pip uninstall opencv-python opencv-contrib-python
  pip install "numpy<2.0" opencv-contrib-python==4.5.5.64

• _ARRAY_API not found or NumPy ABI errors Pin NumPy to <2.0 and reinstall OpenCV:

  pip install --upgrade "numpy<2.0"
  pip install --upgrade opencv-contrib-python==4.5.5.64

• Timeout downloading remote images Check that the URL is reachable and serving an image. Default timeout is 10 seconds.