JPG vs PNG vs WebP: When to Use Each

Introduction

JPG, PNG, and WebP -- three letters (or four) that determine whether your image is crisp or blurry, tiny or bloated, transparent or opaque. Choosing the wrong image format leads to unnecessarily large files, missing transparency, compatibility issues, or visible quality loss.

With WebP now supported by all major browsers, the decision is no longer a simple "JPG for photos, PNG for graphics" binary. This explainer covers the technical strengths and practical trade-offs of each format and gives you a clear decision framework you can apply to any project -- whether you are building a website, designing social media posts, or preparing images for an email newsletter.

JPG (JPEG): The Universal Photo Format

JPEG has been the default image format for photographs since the 1990s, and it remains the most widely supported format across every platform, device, and email client.

How it works: JPG uses lossy compression. The quality slider (0-100%) controls how aggressively the encoder discards data. Lower values produce smaller files but introduce blocking artefacts, especially around sharp edges and text.

Best for:

• Photographs and complex images with millions of colours
• Web images where file size matters most
• Social media posts (most platforms re-encode to JPEG anyway)
• Email newsletters (universal compatibility)

Weaknesses:

• No transparency support -- transparent areas become solid (white by default; customisable in ImageSizr)
• Repeated saves at low quality accumulate artefacts ("generation loss")
• Poor for text, line art, or sharp edges -- lossy encoding blurs them

ImageSizr supports JPEG as both input and output across resize, crop, compress, rotate, and flip tools. Use the Compress JPG tool for dedicated JPEG compression with real-time preview.

PNG: Lossless Quality and Transparency

PNG was designed as a patent-free replacement for GIF and has become the standard format for graphics that require transparency or pixel-perfect precision.

How it works: PNG uses lossless compression. The output is pixel-identical to the source encoding -- no data is discarded. Compression efficiency depends on image complexity, but savings are more modest than lossy formats.

Best for:

• Graphics with sharp edges, text, and line art
• Logos, icons, and UI elements that need transparency
• Screenshots and diagrams
• Any image that will be edited or re-exported multiple times (no generation loss)

Weaknesses:

• Larger file sizes than JPG or WebP for photographic content -- often 3-5x larger
• Not ideal for full-colour photographs where lossy compression delivers equivalent perceived quality at a fraction of the size

ImageSizr preserves PNG transparency across all tools and offers a background-toggle preview (light/dark checkerboard) to verify transparent areas. For detailed guidance on keeping alpha channels intact, read Preserve Transparency When Exporting Images.

Use the Compress PNG tool for PNG-specific workflows.

WebP: The Modern All-Rounder

Developed by Google, WebP is a modern format that supports both lossy and lossless compression, transparency, and animation -- all in a single file format.

How it works: In lossy mode, WebP uses predictive coding based on VP8 video compression. In lossless mode, it uses a combination of transforms and entropy coding. Both modes typically produce smaller files than their JPG/PNG equivalents.

Performance advantages:

• Lossy WebP is typically 25-35% smaller than JPEG at equivalent visual quality
• Lossless WebP is typically 10-25% smaller than PNG
• Supports transparency (alpha channel) in both lossy and lossless modes

Best for:

• Web publishing where performance matters
• Replacing both JPG and PNG when platform/browser support allows
• Progressive web apps and performance-critical sites

Weaknesses:

• Some older software and email clients do not support WebP
• Not universally accepted for print workflows
• Some social media platforms may re-encode to JPEG on upload

ImageSizr can output WebP from any supported input format across all tool families. Use the Resize WebP tool to prepare WebP images at exact dimensions.

Frequently Asked Questions

What image formats are supported?

ImageSizr accepts PNG, JPG/JPEG, WebP, GIF, BMP, TIFF, AVIF, SVG, ICO, and HEIC files as input. Output formats include the original format, JPEG, PNG, WebP, and ICO.

How do I change the output format?

Use the Format dropdown in the toolbar to switch between Original, JPEG, PNG, or WebP before downloading. The file-size estimate updates automatically.

Are my images uploaded to a server?

No. All processing happens directly in your browser. Your images never leave your device, so your data stays private.

What happens to transparency when I compress?

If you export as JPEG, transparency is replaced with a background colour (white by default, or your chosen colour). PNG and WebP preserve transparency. For more detail, read Preserve Transparency When Exporting Images.

Choose the Right Format for Your Next Project

JPG is the reliable choice for photos, PNG is essential when you need transparency or lossless precision, and WebP delivers the best of both worlds for modern web publishing. When in doubt, WebP gives you the smallest file with the most flexibility.

Ready to convert or compress your images? Try ImageSizr's free WebP compression tool -- no sign-up needed, no data leaves your browser.