A single unoptimized hero image can weigh more than your entire web-page budget.

Welcome to your crash course on image compression. In the next 10 minutes you’ll learn:

1. Why images slow sites down (and hurt SEO)
2. Lossy vs. Lossless compression in plain English
3. Key metrics—quality %, resolution, file size
4. Popular formats (JPEG, PNG, WebP, AVIF)
5. A step-by-step demo using SlimImg—no upload, privacy-safe

1. Why Should You Care?

• Performance – every extra 100 KB can add ≈ 0.3 s to Largest Contentful Paint.
• Mobile data cost – users on 4 G pay for each megabyte.
• SEO – Google’s Core Web Vitals ranking factors reward fast pages.
• Accessibility – slim pages load on older devices and poor connections.

🔍 Case study: An e-commerce store compressed all product photos, cut average page size by 68 % and lifted conversion rate by 38 %.

2. Lossy vs. Lossless

Type	How it works	Typical saving	When to use
Lossless	Removes metadata, optimizes entropy without dropping pixels	10–30 %	UI icons, logos, graphics with text
Lossy	Discards detail the eye barely sees	40–90 %	Photos, hero banners, backgrounds

Pro tip: Combine both—first lossless, then gentle lossy.

3. Key Metrics

1. Quality % (q-factor) – lower = smaller file, but more blur.
2. Resolution – serving a 4 K image to a 1080 p viewport wastes pixels.
3. File size – what users actually download.

graph LR;
A[Original 4 MB] -->|Lossless 20 %| B(3.2 MB);
B -->|Resize ×2| C(0.8 MB);
C -->|Lossy q=80| D(0.25 MB);

Example pipeline turning a 4 MB DSLR shot into a 250 KB web-ready hero.

4. Popular Formats at a Glance

Format	Best for	Browser support (2025)	Typical saving vs JPEG
JPEG/JPG	Photos	100 %	baseline
PNG	Transparency, UI	99 %	5–30 % (lossless)
WebP	Web photos + alpha	97 %	25–35 %
AVIF	Next-gen photos, HDR	92 %	30–50 %

5. Hands-On: Compress Your First Image with SlimImg

🕒 Time required: 2 minutes

1. Open https://slimimg.tools
2. Drag & drop your image (JPG / PNG / WebP / AVIF)
3. Adjust the quality slider—preview updates instantly
4. (Optional) Resize or strip EXIF data
5. Download—all processing happens locally; nothing is uploaded

💡 Tip: Need to compress dozens at once? Switch to Bulk Mode and drop a whole folder—the app zips everything automatically.

6. Best-Practice Checklist

• 📐 Serve images at intrinsic size (no 2× waste)
• 🖼️ Use <img srcset> or Next.js <Image> for responsive loading
• 🎨 Choose WebP for photos, PNG-8 / SVG for flat graphics
• 🏷️ Add ALT text after compressing—SEO + accessibility
• 🚀 Test with PageSpeed Insights after each batch

7. Further Reading

• Google Image SEO Best Practices
• Web.dev Use WebP images
• SlimImg 3 Practical Ways to Strip EXIF Metadata & Protect Your Privacy

Ready to Shrink Your First Image?

Give SlimImg a try → Compress Now