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Testing Image Watermark Detection Implementation in Stable Diffusion

This test suite implements watermark detection functionality for the Stable Diffusion project, focusing on verifying the proper decoding of embedded watermarks in images. The test utilizes OpenCV and the imwatermark library to extract and validate watermark data from image files.

Test Coverage Overview

The test coverage focuses on watermark detection capabilities in image files.

Key areas tested include:

Image loading and processing with OpenCV
Watermark extraction using DWT-DCT algorithm
UTF-8 decoding of watermark data
Error handling for invalid watermarks

Implementation Analysis

The testing approach employs a straightforward command-line interface using the Python Fire library for argument parsing. The implementation follows a modular pattern with distinct stages for image loading, watermark detection, and decode validation.

Technical implementation features:

WatermarkDecoder configuration with bytes mode and 136-bit length
DWT-DCT watermark extraction method
Exception handling for UTF-8 decode failures

Technical Details

Testing tools and dependencies:

OpenCV (cv2) for image processing
imwatermark library for watermark detection
Python Fire for CLI argument handling

Configuration details:

Watermark decoder set to ‘bytes’ mode
136-bit watermark length
DWT-DCT extraction algorithm

Best Practices Demonstrated

The test implementation demonstrates several testing best practices for image processing verification.

Notable practices include:

Graceful error handling for decode failures
Clear separation of concerns between image loading and watermark processing
Command-line interface for easy test execution
Modular function design for improved maintainability

stability-ai/stablediffusion

scripts/tests/test_watermark.py

            
import cv2
import fire
from imwatermark import WatermarkDecoder


def testit(img_path):
    bgr = cv2.imread(img_path)
    decoder = WatermarkDecoder('bytes', 136)
    watermark = decoder.decode(bgr, 'dwtDct')
    try:
        dec = watermark.decode('utf-8')
    except:
        dec = "null"
    print(dec)


if __name__ == "__main__":
    fire.Fire(testit)