Images typically account for 40–60% of the total bytes transferred on the average webpage. Despite this, image format selection is often an afterthought — developers grab whatever format the design team exports, upload it, and move on. This leaves significant performance on the table. The difference between the optimal format and a suboptimal one for a given image can easily be a factor of three to ten in file size, with direct consequences for page load time, Core Web Vitals scores, mobile data usage, and hosting costs.
Raster vs Vector: The Fundamental Split
Before comparing specific formats, understanding the raster-vector distinction is essential. Raster images (PNG, JPG, WebP, AVIF, GIF) store color information for a fixed grid of pixels. They are resolution-dependent — enlarging a raster image stretches pixels and degrades quality. They are the appropriate format for photographs, screenshots, complex illustrations, and any image with natural color gradients.
Vector images (SVG) describe shapes, paths, and colors as mathematical operations rather than pixel grids. They scale perfectly to any size without quality loss. They are the appropriate format for logos, icons, diagrams, charts, and any image composed of geometric shapes and flat or gradient fills. SVGs can be embedded inline in HTML (where they can be styled and animated with CSS) or served as external files. For any icon or logo on your website, SVG should be your default choice — a well-optimised SVG is typically 2–10x smaller than an equivalent PNG and renders perfectly at any resolution including high-DPI displays.
JPEG/JPG: Photographs and Continuous-Tone Images
JPEG (Joint Photographic Experts Group) was designed in 1992 specifically for photographic images. It uses lossy compression — the DCT (Discrete Cosine Transform) algorithm — that discards visual information that human perception is less sensitive to, particularly high-frequency detail and subtle color variations. At moderate quality settings (70–85%), JPEG can reduce a photograph's file size by 80–95% compared to uncompressed, with visible quality degradation only at close inspection.
JPEG is the optimal format for photographs, realistic illustrations with many colors, and any image where slight quality reduction is acceptable. It is a poor choice for images with sharp edges, text, flat colors, or transparency. JPEG has no alpha channel (no transparency support) — transparent areas will be filled with a background color, typically white. Images with text or line art will exhibit "ringing" compression artefacts around high-contrast edges at typical quality settings.
JPEG compression quality settings are typically expressed as a percentage or a scale from 1–100. Higher quality means larger file size and less compression artefacting. For most web photographs, quality 70–85 provides an excellent size-quality trade-off. Quality settings above 90 produce rapidly diminishing file size benefits. Quality below 60 produces artefacts that most viewers find objectionable. Our Image Converter uses the browser's Canvas API for JPEG conversion, which typically defaults to quality 80–90.
PNG: Lossless Images with Transparency
PNG (Portable Network Graphics) uses lossless compression — every pixel is reproduced exactly as stored, with no quality degradation. PNG supports full alpha channel transparency (8 bits per pixel, allowing 256 levels of transparency) and can store up to 16 bits per channel (48-bit color) for high-depth images. These properties make it the correct choice for logos, icons, screenshots, UI mockups, images with text, images requiring transparency, and any image that will be edited and re-saved multiple times.
PNG is poorly suited for photographs. Because its compression is lossless, a photograph compressed as PNG will typically be 5–20x larger than the equivalent JPEG at acceptable quality. If you see a photographic PNG on a webpage (particularly a large hero image or background), replacing it with JPEG or WebP is usually the highest-value single performance improvement available.
PNG-8 (256-color palette mode) and PNG-24 (full color) are distinct sub-formats. PNG-8 is appropriate for simple graphics with limited, flat colors — some icons and illustrations — and produces much smaller files than PNG-24. Modern tools and image optimisation pipelines will choose the appropriate sub-format automatically based on the image's color complexity.
APNG (Animated PNG) supports animation, similar to GIF but with full color and alpha channel support. Browser support is universal in modern browsers. For simple animations that need transparency (which GIF cannot provide correctly), APNG or video formats are better alternatives to GIF.
WebP: The Modern Balanced Format
WebP was developed by Google and released in 2010. It supports both lossy and lossless compression, full alpha channel transparency in both modes, and animation. Browser support is universal in all modern browsers (Chrome, Firefox, Safari, Edge) as of 2021. WebP is now the recommended default format for most web images, replacing both JPEG and PNG in many use cases.
For lossy compression (photographs and complex images), WebP typically achieves 25–35% smaller file sizes than JPEG at equivalent visual quality. For lossless compression (graphics, UI elements), WebP is typically 26% smaller than equivalent PNG. The alpha channel support in lossy WebP is particularly valuable — you can have a photographic-quality image with soft, gradient transparency, which is impossible in JPEG and produces large files in PNG.
Converting existing JPEGs and PNGs to WebP is one of the most reliable image performance improvements with no quality trade-off visible to users. Our browser-based Image Converter tool converts between JPG, PNG, and WebP using the Canvas API, with no server upload required. For production workflows, command-line tools like cwebp, Squoosh CLI, or Sharp (Node.js) integrate into build pipelines for automated conversion.
AVIF: The Cutting-Edge Format
AVIF (AV1 Image File Format) is based on the AV1 video codec's intra-frame compression. It provides significantly better compression than WebP — typically 20–50% smaller than WebP at equivalent quality, with particularly impressive results on photographs. AVIF also supports wide color gamut (P3, Rec. 2020), HDR, and has excellent lossless mode performance.
Browser support for AVIF has reached approximately 94% of global browser users as of 2025 (Chrome 85+, Firefox 93+, Safari 16+). For production use, serve AVIF to supported browsers with WebP or JPEG as fallbacks using the HTML picture element. The picture element allows listing multiple source formats in priority order — the browser uses the first format it supports.
AVIF encoding is computationally intensive compared to JPEG and WebP. Encoding a single large AVIF file can take seconds to minutes on a standard server, compared to milliseconds for JPEG. This means AVIF is typically generated at build time or through a dedicated image processing service, not on-the-fly. CDNs like Cloudflare, Cloudinary, and imgix can serve AVIF automatically for supported browsers based on the Accept header, handling the format negotiation transparently.
GIF: Legacy Animation Only
GIF (Graphics Interchange Format) was created in 1987 and is now severely limited by modern standards: 256-color palette (no true color), 1-bit transparency (fully transparent or fully opaque, no alpha gradients), and poor compression. The only remaining legitimate use case for GIF is animated images where video formats are not accepted and where the limited palette and quality are tolerable.
For any new animated content, prefer video (MP4 with H.264, or WebM with VP9/AV1) served with the autoplay muted loop playsinline attributes, or APNG/animated WebP for smaller, simpler animations. A video file for a typical "GIF-style" animation will be 5–20x smaller than the equivalent GIF while providing full color, alpha support, and better quality.
Format Selection Decision Guide
Follow this decision tree: Is the image a photograph or complex realistic image? Use WebP (with JPEG fallback) or AVIF (with WebP fallback). Is it a logo, icon, or simple geometric image? Use SVG if possible, otherwise WebP lossless or PNG. Does it require transparency and contain photographic content? WebP lossy with alpha. Is it a simple flat-color graphic with limited colors and you need broad compatibility? PNG. Does it need to be animated? Animated WebP or video (not GIF). Is it a screenshot of code or a UI with sharp text? PNG or lossless WebP.
Always verify your format choices with actual file size comparisons — theory and practice don't always align. Our Image Converter tool lets you quickly convert between JPG, PNG, and WebP in the browser to compare results. For production-scale image optimisation, integrate an automated pipeline that compresses and format-converts images as part of your build or CDN configuration, removing the manual per-image decision from the deployment workflow.