Strip Photography / Slit Photography

A digital implementation of strip photography (also called slit photography) that captures a two-dimensional image as a sequence of one-dimensional images over time.

Strip photography records a moving scene over time by extracting the same line position from each video frame and assembling them into a composite image where:

• One axis represents space (the slit/line being observed)
• The other axis represents time (progression through video frames)
• Moving objects appear as visible shapes, stationary objects as stripes
• Object width is inversely proportional to speed (faster = narrower, slower = wider)

Usage

Basic Usage - Uses smart defaults (yrow=8, auto output to results/):

uv run main.py .\line500fps32pix.mp4

Output: results/line500fps32pix_a3f2_t0_01.jpg (auto-generated with UUID and threshold)

Row Mode - Extract horizontal lines with custom settings:

uv run main.py .\line500fps32pix.mp4 --yrow 16 --threshold 0.005

With Relax - Include extra frames around threshold frames for smoother transitions:

uv run main.py .\line500fps32pix.mp4 --relax 5
# or use default relax value (100):
uv run main.py .\line500fps32pix.mp4 --relax

Video Mode - Generate MJPEG video showing accumulated scan lines over time:

uv run main.py .\line500fps32pix.mp4 --video --fps 30

Output: results/video/line500fps32pix_a3f2_t0_01_fps30_0.avi

Video with Timestamp - Add frame count overlay to video:

uv run main.py .\line500fps32pix.mp4 --video --fps 30 --timestamp

Alpha Video Mode - Generate PNG sequence with transparency for video editing:

uv run main.py .\line500fps32pix.mp4 --video --alpha --fps 30 --timestamp

Output: results/video/line500fps32pix_a3f2_t0_01_fps30_0_alpha/ (directory with PNG sequence)

Debug Mode - Analyze changes and generate threshold recommendations:

uv run main.py .\line500fps32pix.mp4 --debug

Output: results/debug/line500fps32pix_7c91_t0_01_changes.png

Debug mode generates PowerShell commands to test all suggested thresholds:

0.0087,0.0098,0.0112,0.0121,0.0159 | %{uv run .\main.py video.mp4 --threshold $_}

Setup

Install dependencies with uv:

uv sync

Parameters

Required

• video_file - Path to input video file

Optional

• --xcolumn N - Extract vertical line at x-coordinate (column mode)
• --yrow N - Extract horizontal line at y-coordinate (row mode, default: 8)
• --output PATH - Output file path (default: auto-generated to results/ with UUID)
• --threshold N - Change threshold 0-1 for frame inclusion (default: 0.01)
• --relax [N] - Include N extra frames before/after threshold frames (default: 0, or 100 if flag used without value)
• --debug - Analyze changes without creating strip image, outputs to results/debug/
• --video - Generate MJPEG video showing accumulated scan lines over time
• --fps N - Output video frame rate (default: 30.0, only used with --video)
• --alpha - Generate PNG sequence with alpha transparency for video editing (video mode only)
• --timestamp / --ts - Embed frame count on bottom left corner (video mode only)
• --timeline - Overlay frame numbers as timeline/ruler on output image (image mode only)
• --start N - Start frame number (0-based, default: 0)
• --end N - End frame number (0-based, default: last frame)

Output Modes

• Image mode (default): Creates static strip photography image
  • Column mode: Extracts vertical line (--xcolumn) → Width = frames, Height = video height
  • Row mode: Extracts horizontal line (--yrow, default) → Rotated 90° CW for proper orientation
• Video mode (--video): Creates MJPEG video showing scan line accumulation over time
  • Each frame shows accumulated scan lines up to that point in time
  • Final frame shows complete strip photography image
  • Video dimensions automatically determined by input video and number of significant frames
• Alpha video mode (--video --alpha): Creates PNG sequence with alpha transparency
  • Perfect for video editing with transparent backgrounds instead of black padding
  • Each PNG frame shows progressive scan line accumulation with alpha channel
  • Import as PNG sequence in video editors at specified FPS
  • No keyframe compression - ideal for editing workflows

Features

Smart Defaults:

• Defaults to row mode at y=8 if no mode specified
• Auto-generates output filename with UUID and threshold: results/video_a3f2_t0_01.jpg
• Automatically appends .jpg extension if none provided
• Row mode output is rotated 90° clockwise for proper viewing

Change Detection: Automatically filters frames with minimal changes using configurable thresholds

• Use --threshold (0-1) to control sensitivity
• --debug mode provides threshold recommendations and change analysis
• Higher thresholds = more compression, fewer frames

Relax Feature: Include extra frames around significant changes for smoother transitions

• --relax 5 includes 5 frames before/after each threshold frame
• --relax without value defaults to 100 frames

Threshold Guide:

• 0.001-0.005: High sensitivity (10-30% compression)
• 0.005-0.02: Medium sensitivity (30-70% compression)
• 0.02+: Low sensitivity (70%+ compression)

Output Organization:

• Image mode: results/ folder
• Video mode: results/video/ folder
• Debug mode: results/debug/ folder

Video Mode Features:

• Creates MJPEG AVI files showing scan line accumulation over time
• Each video frame shows the progressive build-up of the strip photography effect
• Configurable frame rate with --fps parameter
• Optional timestamp overlay with --timestamp / --ts showing frame count in bottom left corner
• Video dimensions automatically calculated based on input video and scan line count
• Compatible with both row and column extraction modes
• Timeline overlay not supported in video mode (use image mode with --timeline instead)

Alpha Video Mode Features:

• Creates PNG sequence with BGRA (alpha channel) for video editing
• Transparent background instead of black padding - perfect for compositing
• No keyframe compression - each PNG is independent for smooth editing
• Progressive scan line accumulation with alpha transparency
• Import into video editors as PNG sequence at specified FPS
• Ideal for professional video editing workflows requiring transparency
• Compatible with all major video editors (Premiere, Final Cut, DaVinci Resolve, etc.)