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Concat Node ​

Purpose & Use Cases ​

The concat node combines multiple images horizontally or vertically into a single composite image. It automatically handles alignment and supports flexible input formats for creating image strips, panoramas, and comparison layouts.

Real-World Applications:

  • Before/After Comparisons: Side-by-side image comparisons for treatments, edits, or changes
  • Product Catalogs: Create product strips showing multiple views or variations
  • Social Media Content: Combine multiple images for Instagram carousels or stories
  • Progress Documentation: Show step-by-step processes or time-lapse sequences
  • Report Generation: Combine charts, photos, and diagrams into unified layouts

Concat Demo

Input/Output Specification ​

Inputs ​

  • Image Array: Array of image objects to combine

Outputs ​

  • Combined Image: Single image containing all input images arranged in sequence
  • Expanded Dimensions: Width or height increased to accommodate all images
  • Format Options: Raw image object or encoded file formats

Configuration Options ​

Input/Output Paths ​

  • Input From: msg.payload (default), flow.*, global.*
  • Output To: msg.payload (default), flow.*, global.*

Direction Options ​

  • Right: Images arranged left-to-right horizontally (width increases)
  • Left: Images arranged right-to-left horizontally (width increases)
  • Down: Images stacked top-to-bottom vertically (height increases)
  • Up: Images stacked bottom-to-top vertically (height increases)

Strategy Options ​

Padding Strategies (for dimension mismatches) ​

  • pad-start: Add padding at beginning of smaller images
  • pad-end: Add padding at end of smaller images
  • pad-both: Center smaller images with padding on both sides
  • resize: Resize all images to match largest dimension

Color Configuration ​

  • Padding Color: Background color for padding areas when images have different sizes
  • Default: Black
  • Formats: RGB (rgb(255,0,0))

Output Format Options ​

  • Raw: Standard image object (fastest for processing chains)
  • JPEG: Compressed with quality control
  • PNG: Lossless with transparency support
  • WebP: Modern format with excellent compression

Performance Notes ​

C++ Backend Processing ​

  • Optimized Composition: Efficient memory allocation for composite canvas
  • Alignment Algorithms: Fast positioning calculations for different alignment modes
  • Batch Processing: All images processed in single operation
  • Memory Management: Minimal copying with direct canvas placement

Dimension Handling ​

  • Automatic Sizing: Canvas automatically sized to fit all images
  • Alignment Compensation: Background fill for dimension mismatches
  • Memory Efficiency: Pre-calculates final dimensions to minimize allocations

Real-World Examples ​

Before/After Comparison ​

[Original Image] → [Array-In: pos=0] ┐
[Processed Image] → [Array-In: pos=1] ├→ [Array-Out] → [Concat: Direction=Right, Strategy=pad-both] → [Comparison Strip]

Create side-by-side before/after comparisons with centered alignment.

Product Catalog Strip ​

[Product Photos Array] → [Concat: Direction=Right, Strategy=resize] → [Catalog Strip]

Combine multiple product views, resizing to uniform height.

Progress Timeline ​

[Step 1 Image] → [Array-In: pos=0] ┐
[Step 2 Image] → [Array-In: pos=1] ├→ [Array-Out] → [Concat: Direction=Down, Strategy=pad-both] → [Process Timeline]
[Step 3 Image] → [Array-In: pos=2] ┘

Document multi-step processes vertically with centered alignment.

[Image Array] → [Resize: Same height] → [Concat: Direction=Right, Strategy=pad-start] → [Carousel Image]

Create horizontal image strips for social media.

Report Layout ​

[Chart Image] → [Array-In: pos=0] ┐
[Photo Evidence] → [Array-In: pos=1] ├→ [Array-Out] → [Concat: Vertical] → [Report Section]
[Data Table] → [Array-In: pos=2] ┘

Combine different types of visual content into reports.

Common Issues & Troubleshooting ​

Dimension Mismatches ​

  • Issue: Images with different sizes create alignment problems
  • Solution: Use resize node to standardize dimensions before concat
  • Alternative: Use appropriate alignment settings to handle size differences

Memory Usage with Large Images ​

  • Issue: Concatenating many large images uses significant memory
  • Solution: Resize images to appropriate sizes before concatenation
  • Monitoring: Watch memory usage with large image arrays

Aspect Ratio Problems ​

  • Issue: Combined image has awkward proportions
  • Planning: Consider final aspect ratio when planning image arrangement
  • Solution: Use padding or cropping to improve final composition

Color Consistency ​

  • Issue: Images have different color profiles or brightness
  • Preprocessing: Apply consistent color correction before concatenation
  • Solution: Use filter nodes to normalize appearance