Image optimization with next/image in NextJS - Performance & Optimization

Performance: Image optimization with next/image

HIGH IMPACT

This affects page load speed by reducing image file size and optimizing delivery, improving Largest Contentful Paint (LCP).

Displaying images on a Next.js page

NextJS

import Image from 'next/image';

export default function MyComponent() {
  return <Image src="/photo.jpg" alt="Sample photo" width={800} height={600} />;
}

next/image automatically optimizes image size, formats, and lazy loads offscreen images.

📈 Performance GainReduces image size and load time, improving LCP and reducing data usage.

Displaying images on a Next.js page

NextJS

<img src="/photo.jpg" alt="Sample photo" width="800" height="600" />

This loads the full image without optimization, causing slower load times and larger data usage.

📉 Performance CostBlocks rendering until full image loads; large file size increases LCP.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Standard <img> tag	Minimal	1 reflow per image load	High paint cost for large images	[X] Bad
next/image component	Minimal	Single reflow with optimized image	Lower paint cost due to smaller images	[OK] Good

Rendering Pipeline

next/image optimizes images during build or on-demand, serving smaller files and lazy loading them to reduce layout blocking.

→Network

→Style Calculation

→Layout

→Paint

⚠️ BottleneckNetwork loading of large images delays Layout and Paint stages.

Core Web Vital Affected

LCP

This affects page load speed by reducing image file size and optimizing delivery, improving Largest Contentful Paint (LCP).

Optimization Tips

1Always use next/image for automatic image optimization in Next.js.

2Specify width and height to prevent layout shifts and improve CLS.

3Enable lazy loading to defer offscreen images and speed up initial load.

Performance Quiz - 3 Questions

How does using next/image improve page load performance?

A It disables image loading until user clicks the image.

B It converts images to text to speed up loading.

C It automatically optimizes image size and format to reduce load time.

D It preloads all images at once to avoid delays.

DevTools: Performance

How to check: Record page load and look for image load times and LCP event timing.

What to look for: Shorter image load times and earlier LCP indicate good image optimization.