gst-plugin-linescan/ROLLINGSUM_GUIDE.md

GStreamer Rolling Sum Plugin Guide

Overview

The rollingsum plugin analyzes video frames in real-time by tracking the mean pixel intensity of a specific column across frames. It maintains a rolling window of these values and can drop frames that deviate significantly from the rolling mean, useful for detecting and filtering unstable or anomalous frames.

How It Works

1. Column Analysis: Extracts mean pixel intensity from a specified vertical column
2. Rolling Window: Maintains a circular buffer of recent column means
3. Deviation Detection: Calculates how much each frame deviates from the rolling mean
4. Frame Filtering: Optionally drops frames exceeding the deviation threshold
5. CSV Logging: Records all frame statistics for analysis

Plugin Properties

Property	Type	Default	Description
window-size	int	1000	Number of frames in rolling window (1-100000)
column-index	int	1	Which vertical column to analyze (0-based)
stride	int	1	Row sampling stride (1 = every row)
threshold	double	0.5	Normalized deviation threshold for dropping frames (0.0-1.0)
csv-file	string	NULL	Path to CSV file for logging (NULL = no logging)

Understanding Normalized Deviation

• Range: 0.0 to 1.0
• Calculation: absolute_deviation / 255.0 (for 8-bit video)
• Meaning: Fraction of the full pixel range
  • 0.001 = deviation of ~0.255 pixel values
  • 0.01 = deviation of ~2.55 pixel values
  • 0.1 = deviation of ~25.5 pixel values

Basic Usage

Simple Pipeline

gst-launch-1.0 idsueyesrc config-file=config.ini ! \
  videoconvert ! \
  video/x-raw,format=GRAY8 ! \
  rollingsum window-size=1000 column-index=1 threshold=0.0002 ! \
  autovideosink

With CSV Logging

gst-launch-1.0 idsueyesrc config-file=config.ini exposure=0.5 ! \
  videoconvert ! \
  video/x-raw,format=GRAY8 ! \
  rollingsum window-size=1000 column-index=1 threshold=0.0002 csv-file=output.csv ! \
  fakesink

Debugging

Enable Debug Output

Use the GST_DEBUG environment variable to see detailed plugin operation:

Windows PowerShell

$env:GST_DEBUG="rollingsum:5"; gst-launch-1.0 [pipeline...]

Windows CMD

set GST_DEBUG=rollingsum:5 && gst-launch-1.0 [pipeline...]

Linux/Mac

GST_DEBUG=rollingsum:5 gst-launch-1.0 [pipeline...]

Debug Levels

Level	Output
rollingsum:1	Errors only
rollingsum:2	Warnings
rollingsum:3	Info messages (file open/close)
rollingsum:4	Debug (caps negotiation)
rollingsum:5	Log (all frame processing)

Example Debug Output

0:00:04.029432200 DEBUG rollingsum gstrollingsum.c:436: Extracted column mean: 10.07
0:00:04.032257100 DEBUG rollingsum gstrollingsum.c:466: Frame 1: mean=10.07, rolling_mean=10.07, deviation=0.00 (normalized=0.0000)

Key Fields:

• Frame N: Frame number
• mean: Current frame's column mean
• rolling_mean: Average of last N frames (window-size)
• deviation: Absolute difference
• normalized: Deviation as fraction of 255

Common Debug Scenarios

1. Verify Plugin Loaded

gst-inspect-1.0 rollingsum

Should show plugin details. If not found, check GST_PLUGIN_PATH.

2. Check CSV File Creation

Look for this in debug output:

INFO rollingsum: Opened CSV file: output.csv

3. Monitor Frame Drops

Look for:

DEBUG rollingsum: Dropping frame 42: deviation 0.0005 > threshold 0.0002

4. Verify Caps Negotiation

DEBUG rollingsum: set_caps
DEBUG rollingsum: Video format: GRAY8, 1224x1026

CSV Analysis

CSV Format

The output CSV contains:

frame,column_mean,rolling_mean,deviation,normalized_deviation,dropped
1,10.071150,10.071150,0.000000,0.000000,0
2,10.059454,10.065302,0.005848,0.000023,0
...

Analyze Results

Use the included analysis script:

uv run analyze_sma.py output.csv

Output includes:

• Statistical summary (min/max/mean/std)
• Threshold recommendations based on percentiles
• Standard deviation-based suggestions
• Visualization plots (output_analysis.png)

Interpreting Results

The analysis provides threshold recommendations:

Percentile	Description	Use Case
99th	Drops top 1%	Very conservative, catch only extreme outliers
95th	Drops top 5%	Conservative, good for quality control
90th	Drops top 10%	Balanced, moderate filtering
75th	Drops top 25%	Aggressive, maximum quality

Recommended Thresholds

Based on analysis of stable camera footage:

For General Use

# Conservative (1-2% frame drop)
threshold=0.0003

# Moderate (5-10% frame drop)
threshold=0.0002

# Aggressive (20-25% frame drop)
threshold=0.0001

For Specific Scenarios

High-speed acquisition (minimal processing):

window-size=100 threshold=0.0005

Quality-focused (stable scenes):

window-size=1000 threshold=0.0001

Real-time monitoring (fast response):

window-size=50 threshold=0.0002

Troubleshooting

No frames being dropped (threshold too high)

Symptom: dropped column always 0 in CSV

Solution:

1. Run with CSV logging
2. Analyze with uv run analyze_sma.py output.csv
3. Use recommended threshold from 90th-99th percentile

Too many frames dropped (threshold too low)

Symptom: Most frames have dropped=1, choppy video

Solution:

1. Increase threshold (try doubling current value)
2. Check if column_index is appropriate
3. Verify video is stable (not shaking/moving)

CSV file not created

Check:

1. File path is writable
2. Look for "Opened CSV file" in debug output (GST_DEBUG=rollingsum:3)
3. Verify csv-file property is set correctly

Column index out of range

Symptom:

WARNING rollingsum: Column index 1000 >= width 1224, using column 0

Solution: Set column-index to value < video width

Inconsistent results

Possible causes:

1. Window size too small (< 50 frames)
2. Sampling moving/dynamic content
3. Column contains edge/artifact data

Solutions:

• Increase window-size to 500-1000
• Choose different column-index (avoid edges)
• Use stride=2 or higher for faster processing

Performance Tips

1. Larger window = more stable but slower to adapt to scene changes
2. Stride > 1 reduces computation but less accurate column mean
3. CSV logging has minimal performance impact
4. Debug level 5 can produce massive logs, use only when needed

Integration Examples

Python Script Control

import subprocess

# Run pipeline with CSV logging
subprocess.run([
    'gst-launch-1.0',
    'idsueyesrc', 'config-file=config.ini',
    '!', 'videoconvert',
    '!', 'video/x-raw,format=GRAY8',
    '!', 'rollingsum',
        'window-size=1000',
        'column-index=1',
        'threshold=0.0002',
        'csv-file=output.csv',
    '!', 'fakesink'
])

# Analyze results
subprocess.run(['uv', 'run', 'analyze_sma.py', 'output.csv'])

Adaptive Threshold

Use analysis results to set optimal threshold for next run:

import pandas as pd

# Analyze previous run
df = pd.read_csv('output.csv')
recommended_threshold = df['normalized_deviation'].quantile(0.95)

print(f"Recommended threshold: {recommended_threshold:.6f}")

Developer Notes

Adding New Features

Key files:

• gst/rollingsum/gstrollingsum.c - Main implementation
• gst/rollingsum/gstrollingsum.h - Header/structures
• gst/rollingsum/CMakeLists.txt - Build config

Rebuild After Changes

.\build.ps1  # Windows
./build.sh   # Linux

Testing

# Quick test
gst-inspect-1.0 rollingsum

# Full pipeline test with debug
$env:GST_DEBUG="rollingsum:5"
gst-launch-1.0 videotestsrc ! rollingsum ! fakesink

References

• DESIGN_ROLLINGSUM.md - Design document
• analyze_sma.py - Analysis tool
• GStreamer documentation: https://gstreamer.freedesktop.org/documentation/

Support

For issues or questions:

1. Enable debug output (GST_DEBUG=rollingsum:5)
2. Generate CSV log and analyze
3. Check this guide's troubleshooting section
4. Review debug output for errors/warnings