The Complete Image Format Guide: Which Format Should You Use?

Raster vs Vector: The Fundamental Divide

Before comparing specific formats, you need to understand the two fundamentally different ways images are stored.

Raster images store colour information for every individual pixel. A 1920×1080 raster image stores data for 2,073,600 pixels. The quality is fixed — scale it up and the pixels become visible. JPEG, PNG, WebP, AVIF, and GIF are all raster formats.

Vector images store geometric instructions: "draw a circle here, fill it with this colour, apply this gradient." The renderer calculates pixels on demand at whatever size is requested. A vector image looks identical at 16×16 and 16000×16000. SVG is the only vector format in common web use.

The practical rule: photographs and complex images → raster. Logos, icons, diagrams, illustrations → vector when possible.

JPEG: The Photograph Standard

JPEG (Joint Photographic Experts Group) has dominated photography since 1992 for a simple reason: it achieves extraordinary compression ratios on photographic content. A raw camera image of a landscape might be 24MB. A JPEG at quality 85 of the same scene is often 2–3MB — a 90% reduction — with differences that are invisible to the naked eye at normal viewing distances.

How it works: JPEG uses Discrete Cosine Transform (DCT) compression. It divides the image into 8×8 pixel blocks and converts each block from colour values to a frequency representation. High-frequency data (fine detail) is discarded more aggressively than low-frequency data (broad colour areas). This is why JPEG artifacts appear as blocky patterns — the 8×8 grid becomes visible when compression is pushed too far.

Quality settings and their real-world effects:

• 85–90%: Near-lossless for photographs. Portfolio images, client deliverables, print-quality exports. Files are roughly 45% smaller than raw.
• 75–85%: The web standard. Most website images look identical to uncompressed at this range. Files are 60% smaller than raw.
• 60–75%: Aggressive compression. Suitable for thumbnails and previews. Artifacts are visible under close inspection.
• Below 60%: Heavy blocking artifacts. Acceptable only for placeholder images or where bandwidth is the only concern.

Where JPEG wins: Every photograph, gradient-heavy illustration, and complex scene with millions of colour transitions.

Where JPEG fails: Transparency (not supported — transparent areas render as white or black), text and sharp edges (DCT artifacts are very visible on high-contrast transitions), images requiring repeated re-saves (every save is a new lossy compression — quality degrades cumulatively).

PNG: Lossless Precision

PNG (Portable Network Graphics) stores every pixel exactly as captured — no data is discarded. This makes it the correct choice when pixel-perfect reproduction matters: logos, icons, screenshots, diagrams, and any image containing text.

Two compression modes:

• PNG-24: Full 24-bit colour (16.7 million colours) plus 8-bit alpha channel for transparency. Used for complex images requiring transparency — product photos on white backgrounds, images with soft shadow edges.
• PNG-8: 256-colour palette only. Used for simple graphics with flat colours. Much smaller than PNG-24, but unsuitable for photographic content.

The transparency advantage: PNG's alpha channel supports full 256-level transparency — every pixel can be anywhere from fully opaque to fully transparent, with smooth gradients in between. This is why logos with soft drop shadows require PNG rather than JPEG.

The file size reality: PNG lossless compression means PNG files are larger than JPEG for the same photographic content — often 3–10× larger. A photograph that is 300KB as a JPEG might be 2.5MB as PNG-24. This trade-off is acceptable for images that require transparency or pixel-perfect edges; it is never acceptable for large photographs on web pages.

Where PNG wins: Logos, icons, screenshots, any image with text overlay, images requiring true transparency, images that will be edited and re-saved multiple times (no quality degradation per save).

WebP: The Modern Web Standard

WebP was developed by Google and released in 2010, built on the VP8 video codec. It supports both lossy and lossless compression modes, as well as transparency and animation — making it a direct upgrade over both JPEG and PNG in most scenarios.

Compression advantage:

• WebP lossy is 25–35% smaller than JPEG at equivalent perceived quality.
• WebP lossless is 26% smaller than PNG on average.
• WebP supports transparency (JPEG does not).
• WebP supports animation (PNG does not, though APNG is a non-standard extension).

Browser support in 2026: All major browsers have supported WebP since 2020. Chrome, Firefox, Safari (since 14), Edge, Opera — full support. The only meaningful gap is Internet Explorer (retired, <0.5% usage). For virtually all new web projects, WebP is safe as the primary format.

Progressive serving pattern: For maximum compatibility during any transition period, use the HTML "picture" element to serve WebP with a JPEG fallback:

Example HTML using the picture element:

<picture>

<source srcset="image.webp" type="image/webp">

<img src="image.jpg" alt="Description">

</picture>

Browsers that understand WebP use the source; others fall back to the img element automatically.

Where WebP wins: New web projects targeting modern browsers, any situation where you would previously have used JPEG or PNG (WebP is almost always the better choice for file size), banners, hero images, product photography with transparent backgrounds.

AVIF: The Next Generation

AVIF (AV1 Image File Format) is derived from the AV1 video codec, developed by the Alliance for Open Media. In compression terms it is the most efficient format available — typically 20% smaller than WebP at equivalent quality and 50% smaller than JPEG.

Adoption status (2026): Chrome (85+), Firefox (93+), Safari (16+), Edge (121+). Global browser support sits at approximately 90% of users. Still short of WebP's 99%+ coverage, but growing fast. Internet Explorer, older Safari on macOS Monterey, and some older Android browsers do not support AVIF.

When to adopt AVIF: For large hero images and photography on high-traffic sites, the 20% additional savings over WebP justify the complexity of serving with fallbacks. Use the "picture" element pattern: AVIF → WebP → JPEG fallback.

When to skip AVIF: For small icons, simple graphics, or any project where adding a third format variant increases complexity beyond its value. WebP is the pragmatic sweet spot for 2026.

Encoding speed note: AVIF encoding is significantly slower than JPEG or WebP — important for any server-side image processing pipeline, though irrelevant for static images compressed once at publish time.

GIF: Animation Only

GIF (Graphics Interchange Format) was created in 1987. Its technical limitations are severe by modern standards: 256 colours maximum, no smooth transparency (only binary on/off per pixel), and poor compression for photographic content. The only reason GIF persists in 2026 is animation — it was the only widely supported animated image format for decades.

For stills, never use GIF. A photograph as GIF is degraded to 256 colours and will be larger than a JPEG while looking worse. A logo as GIF supports only on/off transparency (jagged edges, no soft shadows). In every static use case, JPEG, PNG, or WebP is superior.

For animation, GIF is increasingly obsolete. WebP animated is typically 64% smaller than animated GIF for the same content. AVIF animated is even smaller. The "video" element with autoplay, muted, and loop attributes serves animated content more efficiently still. The primary reason to create animated GIFs in 2026 is compatibility with platforms that don't accept video (some social media, messaging apps, email clients).

SVG: Vector for Icons and Diagrams

SVG (Scalable Vector Graphics) is an XML-based vector format. It stores drawing instructions rather than pixel values, which gives it two unique properties: infinite scalability without quality loss, and CSS/JavaScript accessibility (you can animate, style, and interact with individual elements inside an SVG).

File sizes in practice: Simple SVG icons are often 1–10KB. The same icon as a PNG at 2× resolution for high-DPI screens might be 8–40KB. For icons, logos, and illustrations with clean lines and flat colours, SVG is almost always the smallest and sharpest option.

Limitations: SVG cannot represent photographic content — a photograph as SVG would be absurd (either a raster embed inside the SVG wrapper, defeating the purpose, or a vector approximation that looks like a low-resolution illustration). SVG is also more complex to sanitize when accepting user-uploaded SVGs — malicious SVGs can contain JavaScript.

Where SVG wins: Every icon, every logo, every diagram, every illustration with clean lines, every chart or graph, any graphic that needs to look sharp on both 72dpi screen and 300dpi print.

Inline vs external: SVG can be embedded inline in HTML (full CSS/JS access, no additional HTTP request) or referenced as an external file (cacheable, simpler markup). Inline is preferred for interactive/animated SVGs and critical above-the-fold icons; external file is preferred for large reusable graphics.

Decision Matrix: Which Format for Which Use Case

The two-question decision flowchart:

1. Does it need to scale infinitely (logo, icon, diagram)? → SVG

2. Does it need transparency? → WebP (or PNG if WebP support is a concern)

3. Is it a photograph or gradient-heavy image? → WebP (or JPEG for email/broad compatibility)

4. Everything else → WebP

Real File Size Comparison: Same Photo, Six Formats

The following measurements are from a representative 2000×1333px lifestyle photograph (a scene with varied textures, a person, and background detail — a typical hero image):

What this means in practice: Switching from JPEG to WebP on this single image saves 114KB. At 1,000 page loads per day, that is 114MB of data transfer saved daily — and faster load times for every visitor.

Browser Support Table (2026)

Safari added WebP support in version 14 (September 2020). AVIF support came to Safari in version 16 (September 2022). Both are now safe to use without fallbacks for sites targeting modern browsers. Only serve JPEG/PNG fallbacks if you need to support iOS 13 or earlier.

Quick Reference for Web Developers

Default to WebP for everything new. It beats JPEG on size, beats PNG on size when transparency is needed, and browser support is now effectively universal for web use.

Add AVIF for high-impact images. For large hero images on high-traffic pages, the additional 20% size reduction over WebP justifies serving both via "picture" element.

Keep JPEG and PNG for: Email (WebP support in email clients is poor), platforms that don't accept WebP (some CMS, some social APIs), images that need to be opened in older desktop software.

Always use SVG for icons and logos. The file size advantage and infinite scalability make any other choice a mistake unless the logo is photographic.

Never use GIF for stills. If you have an animated GIF and can serve WebP animated or a looping muted video instead, do — you will almost always save 50–70% in file size.

Set explicit width and height attributes on all "img" elements to prevent layout shift (CLS). Reserve space before the image loads.

Compress before uploading to your CMS or CDN. Most file size wins come from initial compression, not runtime conversion. Use the tools linked throughout this guide to compress images in your browser — no uploads, no privacy concerns.