Smart Crop

Content-aware image cropping that automatically finds the most interesting region.

Overview

Smart crop uses saliency detection, edge detection, and the rule of thirds to identify the best crop region for any aspect ratio. No manual coordinates needed.

Functions

smartCrop

Crop an image to the best region for the given aspect ratio.

function smartCrop(input: Buffer, options: SmartCropOptions): Promise<Buffer>
function smartCropSync(input: Buffer, options: SmartCropOptions): Buffer

Parameters

Parameter	Type	Description
input	Buffer	Image buffer (JPEG, PNG, WebP, etc.)
options	SmartCropOptions	Crop options

Returns

Buffer - Cropped image in PNG format

Example

import { smartCrop } from 'bun-image-turbo';

const buffer = Buffer.from(await Bun.file('photo.jpg').arrayBuffer());

// Square crop for Instagram
const square = await smartCrop(buffer, { aspectRatio: '1:1' });

// YouTube thumbnail
const youtube = await smartCrop(buffer, { aspectRatio: '16:9' });

// Portrait for Stories
const portrait = await smartCrop(buffer, { aspectRatio: '9:16' });

---

smartCropAnalyze

Get the optimal crop coordinates without actually cropping.

function smartCropAnalyze(input: Buffer, options: SmartCropOptions): Promise<SmartCropAnalysis>
function smartCropAnalyzeSync(input: Buffer, options: SmartCropOptions): SmartCropAnalysis

Parameters

Parameter	Type	Description
input	Buffer	Image buffer
options	SmartCropOptions	Crop options

Returns

SmartCropAnalysis object:

Property	Type	Description
x	number	X coordinate of the crop
y	number	Y coordinate of the crop
width	number	Width of the crop
height	number	Height of the crop
score	number	Quality score (higher is better)

Example

import { smartCropAnalyze, crop } from 'bun-image-turbo';

const buffer = Buffer.from(await Bun.file('photo.jpg').arrayBuffer());

// Analyze the best crop
const analysis = await smartCropAnalyze(buffer, { aspectRatio: '1:1' });
console.log(`Best crop: x=${analysis.x}, y=${analysis.y}`);
console.log(`Size: ${analysis.width}x${analysis.height}`);
console.log(`Score: ${analysis.score}`);

// Apply the crop yourself if needed
const cropped = await crop(buffer, {
  x: analysis.x,
  y: analysis.y,
  width: analysis.width,
  height: analysis.height
});

---

Types

SmartCropOptions

interface SmartCropOptions {
  width?: number;           // Target width
  height?: number;          // Target height
  aspectRatio?: AspectRatio; // Aspect ratio string
  boost?: SmartCropBoostRegion[]; // Areas to prioritize
}

AspectRatio

Common aspect ratios:

Ratio	Use Case
1:1	Square (Instagram, profile pics)
16:9	Landscape (YouTube, Twitter)
9:16	Portrait (Stories, TikTok)
4:3	Classic photo
3:2	DSLR standard
21:9	Ultrawide

You can also use any custom ratio like "5:4" or "2:1".

SmartCropBoostRegion

interface SmartCropBoostRegion {
  x: number;      // X coordinate
  y: number;      // Y coordinate
  width: number;  // Region width
  height: number; // Region height
  weight: number; // Priority (0.0 - 1.0)
}

---

Algorithm

Smart crop evaluates potential crop regions using:

1. Saliency Detection - Finds visually interesting areas (high contrast, saturated colors, skin tones)
2. Edge Detection - Preserves areas with important details
3. Rule of Thirds - Prefers compositions with subjects at intersection points

The algorithm scores each potential crop and returns the highest-scoring region.

---

Performance

Image Size	Time
640x480	~15-20ms
1920x1080	~40-60ms
4000x3000	~100-150ms

---

Use Cases

Social Media Thumbnails

async function generateThumbnails(buffer: Buffer) {
  return {
    instagram: await smartCrop(buffer, { aspectRatio: '1:1' }),
    youtube: await smartCrop(buffer, { aspectRatio: '16:9' }),
    twitter: await smartCrop(buffer, { aspectRatio: '16:9' }),
    tiktok: await smartCrop(buffer, { aspectRatio: '9:16' }),
  };
}

Profile Picture Generator

async function generateProfilePic(upload: Buffer) {
  const cropped = await smartCrop(upload, { aspectRatio: '1:1' });
  // Resize to standard sizes
  const sizes = await Promise.all([
    resize(cropped, { width: 32, height: 32 }),   // Tiny
    resize(cropped, { width: 64, height: 64 }),   // Small
    resize(cropped, { width: 128, height: 128 }), // Medium
    resize(cropped, { width: 256, height: 256 }), // Large
  ]);
  return sizes;
}

E-commerce Product Images

async function generateProductImages(product: Buffer) {
  return {
    thumbnail: await smartCrop(product, { aspectRatio: '1:1' }),
    card: await smartCrop(product, { aspectRatio: '4:3' }),
    hero: await smartCrop(product, { aspectRatio: '21:9' }),
  };
}