flutter_bicubic_resize

Fastest image resize, crop and compress for Flutter. 3-4x faster than other libraries. Created and supported by Codigee.

Features

• 3-4x faster than other Flutter image libraries (pure native C pipeline)
• 100% Native C performance (stb_image + stb_image_resize + stb_image_write)
• Identical results on iOS and Android
• Bicubic interpolation (Catmull-Rom, same as OpenCV)
• Full native pipeline: decode -> resize -> encode (no Dart image libraries)
• RGB and RGBA support
• JPEG and PNG support with alpha channel preservation
• EXIF orientation support - automatically rotates JPEG images correctly
• Flexible crop system - anchor position, aspect ratio modes, custom ratios
• Edge handling modes - clamp, wrap, reflect, zero
• PNG compression control - adjustable compression level
• Zero external Dart dependencies (only ffi)

Installation

Add to your pubspec.yaml:

dependencies:
  flutter_bicubic_resize: ^1.2.2

Or run:

flutter pub add flutter_bicubic_resize

Usage

Resize JPEG

import 'package:flutter_bicubic_resize/flutter_bicubic_resize.dart';

final resized = BicubicResizer.resizeJpeg(
  jpegBytes: originalBytes,
  outputWidth: 224,
  outputHeight: 224,
  quality: 95, // optional, default 95
);

Resize PNG

final resized = BicubicResizer.resizePng(
  pngBytes: originalBytes,
  outputWidth: 224,
  outputHeight: 224,
  compressionLevel: 6, // optional, 0-9 (default: 6)
);

Resize raw RGB/RGBA bytes

// RGB (3 bytes per pixel)
final resizedRgb = BicubicResizer.resizeRgb(
  input: rgbBytes,
  inputWidth: 1920,
  inputHeight: 1080,
  outputWidth: 224,
  outputHeight: 224,
);

// RGBA (4 bytes per pixel)
final resizedRgba = BicubicResizer.resizeRgba(
  input: rgbaBytes,
  inputWidth: 1920,
  inputHeight: 1080,
  outputWidth: 224,
  outputHeight: 224,
);

Custom filter selection

// Use different bicubic filter
final resized = BicubicResizer.resizeJpeg(
  jpegBytes: originalBytes,
  outputWidth: 224,
  outputHeight: 224,
  filter: BicubicFilter.mitchell, // or .cubicBSpline
);

Available filters:

• BicubicFilter.catmullRom - Default. Same as OpenCV/PIL. Best for ML.
• BicubicFilter.cubicBSpline - Smoother, more blurry.
• BicubicFilter.mitchell - Balanced between sharp and smooth.

Crop with anchor position

Control where the crop is taken from:

// Crop from top of image (good for portraits)
final portrait = BicubicResizer.resizeJpeg(
  jpegBytes: photoBytes,
  outputWidth: 224,
  outputHeight: 224,
  crop: 0.8,
  cropAnchor: CropAnchor.topCenter,
);

Available anchors:

┌─────────────────┐
│ TL    TC    TR  │   topLeft, topCenter, topRight
│                 │
│ CL  CENTER  CR  │   centerLeft, center (default), centerRight
│                 │
│ BL    BC    BR  │   bottomLeft, bottomCenter, bottomRight
└─────────────────┘

Crop aspect ratio modes

Control the shape of the crop:

// Square crop (default) - 1:1 aspect ratio
final square = BicubicResizer.resizeJpeg(
  jpegBytes: originalBytes,
  outputWidth: 224,
  outputHeight: 224,
  cropAspectRatio: CropAspectRatio.square,
);

// Keep original proportions
final proportional = BicubicResizer.resizeJpeg(
  jpegBytes: originalBytes,
  outputWidth: 800,
  outputHeight: 600,
  cropAspectRatio: CropAspectRatio.original,
);

// Custom aspect ratio (16:9)
final widescreen = BicubicResizer.resizeJpeg(
  jpegBytes: originalBytes,
  outputWidth: 1920,
  outputHeight: 1080,
  cropAspectRatio: CropAspectRatio.custom,
  aspectRatioWidth: 16.0,
  aspectRatioHeight: 9.0,
);

Edge handling modes

Control how pixels outside the image bounds are handled:

// Wrap mode - creates tiled pattern
final tiled = BicubicResizer.resizeJpeg(
  jpegBytes: textureBytes,
  outputWidth: 512,
  outputHeight: 512,
  edgeMode: EdgeMode.wrap,
);

Available modes:

• EdgeMode.clamp - Default. Repeat edge pixels.
• EdgeMode.wrap - Tile/repeat image (wrap around).
• EdgeMode.reflect - Mirror reflection at edges.
• EdgeMode.zero - Black/transparent pixels outside bounds.

EXIF orientation control

For JPEG images, EXIF orientation is applied by default. You can disable it:

// Get raw pixel orientation (ignore EXIF)
final raw = BicubicResizer.resizeJpeg(
  jpegBytes: photoBytes,
  outputWidth: 224,
  outputHeight: 224,
  applyExifOrientation: false,
);

Complete example with all options

final result = BicubicResizer.resizeJpeg(
  jpegBytes: originalBytes,
  outputWidth: 1920,
  outputHeight: 1080,
  quality: 90,
  filter: BicubicFilter.catmullRom,
  edgeMode: EdgeMode.clamp,
  crop: 0.9,
  cropAnchor: CropAnchor.center,
  cropAspectRatio: CropAspectRatio.custom,
  aspectRatioWidth: 16.0,
  aspectRatioHeight: 9.0,
  applyExifOrientation: true,
);

Why?

Default platform APIs use different algorithms:

• Android: Typically Bilinear
• iOS: Depends on context (Lanczos, Bilinear, etc.)

This package uses the same C code on both platforms, ensuring identical output for the same input.

Architecture

The entire image processing pipeline runs in native C code:

1. Decode - stb_image decodes JPEG/PNG to raw pixels
2. EXIF orientation - For JPEG: parses EXIF metadata and applies correct rotation/flip (optional)
3. Crop - Extracts region based on anchor position and aspect ratio mode
4. Resize - stb_image_resize2 applies bicubic interpolation with selected edge mode
5. Encode - stb_image_write encodes back to JPEG/PNG

This means:

• No Dart image libraries needed
• Minimal memory overhead
• Maximum performance
• Consistent results across platforms
• Photos from mobile cameras display correctly (no rotation issues)

Algorithm

Uses stb_image_resize2 with STBIR_FILTER_CATMULLROM (Catmull-Rom spline).

This is the same algorithm used by:

• OpenCV cv2.INTER_CUBIC
• PIL/Pillow Image.BICUBIC

Perfect for ML preprocessing (OpenCLIP, ResNet, etc.) where consistent results with training pipeline matter.

Performance

3-4x faster than other Flutter image libraries. The entire pipeline runs in native C code - no Dart image processing overhead. Operations are synchronous but extremely fast:

• Resize 4K JPEG to 224x224: ~15-30ms
• Crop + resize + compress in single pass
• No memory copying between Dart and native (direct FFI)

Requirements

• Flutter 3.0+
• Android SDK 21+
• iOS 11.0+

Sponsor

CODIGEE.COM

Documentation

• API Reference - Complete API documentation
• Example App - Working demo application

License

MIT License - see LICENSE file.

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