What are the main image formats and when should I use each?

JPEG: photos and complex images — best compression for photographic content. PNG: logos, screenshots, images needing transparency — lossless, larger files. WebP: best for web — smaller than JPEG/PNG at equal quality, supports transparency. SVG: icons, logos, diagrams — vector format, scales infinitely, editable with CSS. AVIF: next-gen format — even smaller than WebP but limited tool support. GIF: simple animations only.

What is the difference between lossy and lossless compression?

Lossy compression (JPEG, WebP lossy) permanently removes image data — you choose how much quality to trade for size. Once saved, you cannot recover the discarded data. Lossless compression (PNG, WebP lossless, GIF) rearranges data without removing anything — the decompressed image is pixel-identical to the original. Use lossless for source files and logos; lossy for web delivery.

What is WebP and should I switch from JPEG?

WebP is an image format developed by Google that delivers 25–35% smaller file sizes than JPEG at equivalent perceptual quality, and 25–50% smaller than PNG for lossless images. All modern browsers (Chrome, Firefox, Safari 14+, Edge) support WebP. For new websites, use WebP as the primary format and provide JPEG fallbacks for legacy support if needed.

What is AVIF and should I use it?

AVIF (AV1 Image File Format) is the newest major image format, offering 50% smaller files than JPEG at equivalent quality — even better than WebP. Browser support reached 90%+ in 2024. The trade-off is slow encoding (converting images to AVIF takes significantly longer than WebP). Use AVIF where encoding time is acceptable; use WebP as the safe default for now.

Image Formats Explained: JPG, PNG, WebP, SVG, GIF, and When to Use Each

Why Image Format Choice Has Real Performance Consequences#

Images typically account for 50–75% of a webpage's total file size. Choosing the wrong format for a given use case can mean delivering a file three to ten times larger than necessary, directly degrading Core Web Vitals scores and page load speed. Google's Lighthouse audit explicitly flags oversized and wrongly-formatted images. Conversely, choosing the right format and compression level at the point of creation — before uploading to a CMS or social platform — eliminates a major class of performance problem with no visible quality loss. The browser Image API and Canvas API mean all format conversions can happen locally without software.

JPEG: The Right Choice for Photographs#

JPEG (Joint Photographic Experts Group) uses lossy compression that is specifically optimised for the continuous tonal gradations of photographs. It achieves dramatically smaller files than PNG for photo content — typically 60–80% smaller at quality settings of 80–85 where the difference is imperceptible to most viewers. JPEG does not support transparency; any area that needs a transparent background will be filled with white. JPEG is not suitable for graphics with sharp edges, text, or flat colour areas — these suffer from visible compression artefacts (blocky distortions around edges). Use JPEG for all photographic content: product shots, lifestyle images, portrait photos.

PNG: When You Need Lossless or Transparency#

PNG (Portable Network Graphics) uses lossless compression — every pixel is preserved exactly. This makes it ideal for graphics that contain text, logos, icons, or any design element where sharpness matters. PNG supports an alpha channel (transparency), which is essential for overlaying graphics on different backgrounds. PNG files are significantly larger than JPEG for photographic content — a 2 MB JPEG photograph might be 8–10 MB as PNG. Use PNG for: logos and wordmarks, interface screenshots, graphics with text overlay, images that need transparent backgrounds. Use the JPG to PNG converter at allio.tools/jpg-to-png/ or PNG to JPG converter at allio.tools/png-to-jpg/ when you need to switch.

WebP: The Modern Default for Web Images#

WebP is Google's open image format, supported by all modern browsers since 2020. It achieves 25–34% smaller files than JPEG and 26% smaller than PNG at equivalent quality. Critically, WebP supports both lossy compression (for photographs) and lossless compression (for graphics), making it a single format that handles both use cases better than either JPEG or PNG individually. WebP also supports transparency and animation. For any new web project, WebP should be the default format for all images. The WebP Converter at allio.tools/webp-converter/ converts JPEG, PNG, and other formats to WebP in seconds, entirely in the browser.

SVG: Scalable Vector Graphics for Icons and Illustrations#

SVG (Scalable Vector Graphics) is fundamentally different from raster formats like JPEG and PNG. Instead of storing pixel data, SVG stores mathematical descriptions of shapes, lines, and curves. This means SVG files scale to any size without any loss of quality — the same file looks perfect at 16×16 pixels and at 4000×4000 pixels. SVG files are also typically much smaller than raster equivalents for simple graphics: a logo as SVG might be 2–5 KB; as PNG at print resolution it might be several megabytes. SVG is the correct format for logos, icons, illustrations, and any graphic that needs to display across devices at different resolutions. Use SVG to PNG at allio.tools/svg-to-png/ when you need a raster export for platforms that do not accept SVG.

GIF and AVIF: Animation and the Next Generation#

GIF (Graphics Interchange Format) is the oldest surviving web image format, now used almost exclusively for short animations. Its 256-colour limit makes it poor for photographic content but it remains widely supported across every platform. For new animated content, WebP animation and the newer AVIF format offer dramatically better compression. AVIF (AV1 Image File Format) achieves 50% smaller files than JPEG with equivalent quality and has near-universal browser support as of 2024. It is not yet as widely supported in image editing tools, but support is growing rapidly. For now, WebP is the practical modern choice and AVIF is the emerging standard to watch.

ICO: The Format Nobody Thinks About Until It Is Missing#

ICO files are used for website favicons — the small icons that appear in browser tabs, bookmark lists, and mobile home screens. A proper favicon implementation requires an ICO file (for legacy browser compatibility) plus PNG files at multiple sizes (16×16, 32×32, 192×192, 512×512). The ICO Converter at allio.tools/ico-converter/ converts any PNG or JPEG to ICO format. For the full set of favicon sizes, use the Favicon Generator at allio.tools/favicon-generator/, which takes a single source image and exports all required sizes in one download. Forgetting to implement favicons is a small but visible professionalism gap — the missing icon in a browser tab makes a website look unfinished.

Quick Decision Guide: Which Format for Which Use Case#

Photograph for a webpage: WebP (first choice) or JPEG (fallback for environments with limited WebP support). Logo or icon that needs to scale: SVG. Logo or icon exported for a platform that requires raster: PNG. Graphic with transparent background: WebP or PNG. Interface screenshot: PNG. Animation: WebP animation or GIF for maximum compatibility. Website favicon: ICO plus PNG at multiple sizes. Email image: JPEG or PNG (most email clients have limited WebP support). Social media upload: JPEG or PNG at the platform's specified dimensions (avoid WebP for social, where re-compression behaviour varies). Thumbnail grid on a website: WebP, compressed to under 50 KB each.