Image File Types: A Comprehensive Guide to Formats and Uses

What are the main image file types?

The main image file types are JPEG, PNG, WebP, GIF, SVG, and AVIF, and each is built for a different job: photos, graphics, transparency, animation, or scalability. Choosing the right one matters because image format directly affects how fast a page loads, and modern formats like WebP are often 25 to 34% smaller than JPEG (Google). This guide explains each format, the difference between raster and vector, and how to pick the right one.

Key Takeaways

• The common web formats are JPEG (photos), PNG (graphics and transparency), WebP and AVIF (modern, smaller), GIF (simple animation), and SVG (scalable graphics).
• Raster images are made of pixels and lose quality when enlarged; vector images (SVG) scale to any size without loss (MDN).
• WebP is often 25 to 34% smaller than JPEG, making it the default choice for web photos (Google).
• PNG is lossless with transparency, ideal for logos, screenshots, and graphics you’ll edit.
• The right format balances quality, file size, and compatibility for the specific use.

Format choice is part of image performance, so this pairs with our guide to converting WebP to PNG and the wider work in improving Core Web Vitals.

What’s the difference between raster and vector images?

Raster images are made of a fixed grid of pixels, while vector images are made of mathematical paths that can scale to any size without losing quality (MDN). This single distinction explains why some formats blur when enlarged and others stay crisp at any size.

Raster formats, which include JPEG, PNG, WebP, GIF, and AVIF, store an exact pixel for every point in the image. They’re perfect for photographs and detailed images, but enlarging them past their native resolution makes them look blocky or blurry, because there’s no extra detail to draw. Vector formats, chiefly SVG on the web, store shapes as instructions (“draw a circle here, fill it with this colour”) rather than pixels, so they render perfectly sharp at any size, from a favicon to a billboard. The trade-off is that vectors suit graphics, logos, and icons with defined shapes, not photographs, which have too much organic detail to describe as paths. Knowing which you’re dealing with is the first step in choosing a format.

When should you use JPEG?

Use JPEG for photographs and complex images with many colours, where its lossy compression shrinks file size dramatically with little visible quality loss (MDN). It’s the most widely supported image format in the world, so a JPEG opens everywhere.

JPEG works by discarding image data the human eye is unlikely to notice, which makes files small but means quality degrades a little each time you re-save. That’s fine for final photos on a web page, but poor for images you’ll edit repeatedly or for graphics with sharp edges and flat colour, where the compression creates visible artefacts around lines and text. JPEG also doesn’t support transparency. In short, reach for JPEG when you have a photograph to display and file size matters, but choose something else for logos, screenshots, or anything needing a transparent background.

When should you use PNG?

Use PNG for graphics, logos, screenshots, and any image that needs transparency or must stay pixel-perfect, because PNG is lossless and supports a full alpha-transparency channel (MDN). Lossless means it preserves every pixel exactly, with no compression artefacts.

That makes PNG the right choice wherever quality and crisp edges matter more than the smallest possible file: a logo with a transparent background, a screenshot with fine text, or an image you’ll edit and re-save without accumulating damage. The trade-off is size, PNG files are larger than JPEG or WebP for the same image, because lossless compression keeps everything. PNG is also universally supported, which is why it’s a common conversion target when a tool can’t open a newer format, as covered in our guide to converting WebP to PNG. Use PNG for graphics and transparency; don’t use it for large photographs where its size is wasteful.

When should you use WebP and AVIF?

Use WebP and AVIF for images on a live website, because both are modern formats designed to be much smaller than JPEG and PNG while keeping quality high (Google). WebP is often 25 to 34% smaller than comparable JPEG, and AVIF can compress even further.

These newer formats support both lossy and lossless compression and transparency, combining the strengths of JPEG and PNG in smaller files. WebP is now supported in all major browsers, making it a safe default for web images (MDN). AVIF offers the best compression of the common formats but has slightly less universal support and is slower to encode, so it’s often served with a fallback. The practical pattern is to use WebP or AVIF for the images visitors download, since smaller files load faster and improve Core Web Vitals, while keeping a lossless master (PNG or the original) for editing. The main catch with both is outside the browser: some older desktop software still can’t open them.

When should you use GIF?

Use GIF only for simple, short animations, because that’s the one job it still does that other common formats don’t, but it’s a poor choice for static images (MDN). GIF is limited to 256 colours, so photographs look banded and washed out, and its file sizes are large for the quality it delivers.

For a static graphic, PNG is better; for a photo, JPEG or WebP. GIF’s surviving niche is the short looping animation, though even there, modern video formats or animated WebP usually deliver better quality at smaller sizes. If you inherit GIFs on a site, they’re often worth converting: a short MP4 or WebM video can replace an animated GIF at a fraction of the file size. Treat GIF as a legacy format you’ll occasionally encounter rather than one you reach for by choice.

When should you use SVG?

Use SVG for logos, icons, and simple graphics, because as a vector format it scales to any size without losing sharpness and usually has a tiny file size (MDN). An SVG logo looks crisp on a phone and on a 4K display from the same small file.

Because SVGs are defined as text (XML describing shapes), they’re small, scalable, and can even be styled and animated with CSS, which makes them ideal for responsive design where one asset must work at many sizes. They’re perfect for logos, icons, simple illustrations, and charts, anything built from defined shapes rather than photographic detail. SVG is the wrong choice for photographs, which can’t be described efficiently as paths. One practical note: because SVGs are code, only use ones from sources you trust, since a malicious SVG can carry scripts. For brand assets and interface icons, though, SVG is usually the best format available.

How do you choose the right image format?

You choose the right format by matching it to the image’s content and use: photos to JPEG or WebP, graphics and transparency to PNG, scalable logos to SVG, and modern web images to WebP or AVIF (Google). Three questions get you most of the way there.

First, is it a photograph or a graphic? Photos suit JPEG, WebP, or AVIF; graphics, logos, and screenshots suit PNG or SVG. Second, does it need to scale? If it must look sharp at many sizes, use SVG. Third, where will it be used? For the live web, prefer WebP or AVIF for speed; for editing or maximum compatibility, use PNG or the original. The table below sums it up.

The common pattern in practice is to keep lossless masters (PNG or originals) for editing and serve WebP or AVIF to visitors, with SVG for anything vector. Match the format to the job and you get the best balance of quality, size, and compatibility.

How do you optimise images for the web?

Choosing the right format is half the job; the other half is optimising each image so it’s as small as it can be without looking worse, since unoptimised images are one of the most common causes of slow pages. A simple, repeatable workflow handles it.

Work through four steps for every image you publish:

1. Resize to the dimensions you actually display. Don’t upload a 4000px photo to show it at 800px, scale it down first, since oversized images waste bandwidth for no visible gain.
2. Compress it. Run it through a compression tool to strip unnecessary data. Browser-based tools like Squoosh, and services like TinyPNG or ShortPixel, cut file size significantly while keeping quality acceptable; ImageOptim is a good desktop option.
3. Serve a modern format. Export or convert to WebP (or AVIF) for the web, smaller than JPEG or PNG at the same quality, while keeping a lossless master for editing.
4. Lazy-load below-the-fold images. Add loading="lazy" so off-screen images load only as the user scrolls, but never lazy-load your largest above-the-fold image.

For an ongoing site, automate this rather than doing it by hand: most CMS platforms have an image-optimisation plugin (or a CDN) that resizes, compresses, and serves WebP or AVIF automatically on upload. The payoff is faster pages and better Core Web Vitals, which our guide to improving Core Web Vitals covers in full. Optimise once as part of your publishing routine and every page benefits.

Final thoughts

There’s no single best image format, only the right one for each job. Use JPEG or WebP for photographs, PNG for graphics and transparency, SVG for logos and icons that must scale, and WebP or AVIF for fast-loading web images. Remember the raster-versus-vector distinction: pixels for photos, paths for graphics that need to scale. The practical workflow for most sites is to keep lossless masters for editing and serve modern, compressed formats to visitors, which gives you both quality and speed. When you need to move between formats, our guide to converting WebP to PNG walks through the how, and improving Core Web Vitals covers the wider performance picture.