The Complete Guide to Image Formats: JPEG, PNG, WebP, AVIF, and GIF Explained
Everything you need to know about image formats — how they work, when to use each one, and how to choose the right format for your project.
How Digital Images Work
Before diving into formats, it helps to understand what a digital image actually is: a grid of pixels, each with a colour value. A 1920 × 1080 image contains roughly two million pixels. If each pixel stores three colour channels (red, green, blue) at 8 bits each, the raw uncompressed data is about 6 MB.
Image formats exist to make this data smaller. They use mathematical algorithms to represent the same visual information more efficiently — either by discarding data the eye can't distinguish (lossy), or by finding more compact ways to represent the same data (lossless).
JPEG — Deep Dive
Full name: Joint Photographic Experts Group Year introduced: 1992 Compression: Lossy Transparency: No Animation: No
How JPEG compression works
JPEG divides the image into 8 × 8 pixel blocks, then applies a Discrete Cosine Transform (DCT) to each block. This converts the pixel data into frequency components. High-frequency components (fine detail) are then quantised (rounded) more aggressively than low-frequency components (broad colour areas). The quality setting controls how aggressively this quantisation is applied.
This is why JPEG artefacts — blocky patterns, colour fringing around edges — appear first in areas of fine detail and sharp contrast.
When to use JPEG
JPEG excels at photographic content because photographs tend to have gradually changing colours and many subtle tonal variations. The compression algorithm is specifically designed for this type of content.
Use JPEG when:
- The image is a photograph
- Transparency is not needed
- You need universal compatibility (older systems, email, print workflows)
- File size is more important than pixel-perfect accuracy
JPEG quality settings
The quality scale (1–100) is not linear in terms of file size or visual impact. The relationship is roughly logarithmic — going from quality 95 to 100 roughly doubles the file size, while going from 75 to 80 makes a much smaller difference.
Practical quality ranges:
- 85–95: High quality for important images (product photos, portfolio)
- 75–85: Standard web quality — indistinguishable from higher settings at normal viewing distances
- 60–75: Aggressive compression for thumbnails and background images
- Below 60: Visible artefacts; not recommended
PNG — Deep Dive
Full name: Portable Network Graphics Year introduced: 1996 Compression: Lossless (DEFLATE) Transparency: Full alpha channel (8-bit) Animation: No (APNG variant supports animation)
How PNG compression works
PNG uses a two-stage process. First, a filter predicts each pixel's value based on its neighbours and stores only the difference (the prediction error). Then DEFLATE compression (the same algorithm used in ZIP files) compresses the filtered data.
Because this process is lossless, the original pixel values can always be recovered perfectly. This makes PNG ideal for images that will be further edited or processed.
When to use PNG
PNG is the correct choice whenever you need:
- Transparent backgrounds (logos on coloured backgrounds, cut-out product photos)
- Pixel-perfect accuracy (screenshots, interface mockups, medical imaging)
- Images with text or line art (the sharp edges that cause JPEG artefacts are preserved perfectly)
- Source files that will be edited and re-exported
Never use PNG for photographs — the lossless compression means files will be 3–5× larger than equivalent JPEGs with no visible improvement.
WebP — Deep Dive
Full name: Web Picture format Year introduced: 2010 (Google) Compression: Both lossy and lossless Transparency: Full alpha channel Animation: Yes
How WebP compression works
WebP's lossy mode is based on the VP8 video codec, which uses block-based prediction similar to JPEG but with more sophisticated intra-frame prediction modes. The lossless mode uses a different algorithm entirely, including palette coding, backward references (referring to earlier parts of the image for repeated patterns), and entropy coding.
The result is consistently smaller files than JPEG for lossy and smaller than PNG for lossless, at the same perceived quality.
When to use WebP
WebP should be your default format for all web images in 2025. Use it for:
- Photographs (smaller than JPEG)
- Graphics with transparency (smaller than PNG)
- Animated images (smaller than GIF)
- Any image on a public-facing website
The only reason to avoid WebP is legacy compatibility — some older native apps, email clients, and image editing software still don't support it.
AVIF — Deep Dive
Full name: AV1 Image File Format Year introduced: 2018 Compression: Lossy and lossless Transparency: Yes Animation: Yes (AVIS)
How AVIF compression works
AVIF is based on a single frame of AV1 video, which uses state-of-the-art video compression techniques: adaptive block partitioning, directional intra prediction, and sophisticated entropy coding. This results in better compression than WebP at the cost of slower encoding.
When to use AVIF
AVIF is the best choice for:
- Maximum compression where encoding time isn't critical
- Wide colour gamut images (HDR photography, digital art)
- Sites targeting modern browsers where you can verify support
The trade-off: AVIF encoding is 5–10× slower than WebP encoding, which matters for server-side on-the-fly conversion but not for pre-processed assets.
GIF — Deep Dive
Full name: Graphics Interchange Format Year introduced: 1987 Compression: Lossless (LZW) Transparency: 1-bit (on/off only) Animation: Yes (frame-based)
GIF is limited to 256 colours per frame and uses 1-bit transparency (a pixel is either fully transparent or fully opaque). It was the format of the early web and remains in use primarily because of its universal animation support and cultural familiarity.
For new animated content, WebP animated images are typically 60–70% smaller than GIF. For complex animations, consider video formats (MP4, WebM) which offer far better compression.
Choosing the Right Format: Quick Reference
| Scenario | Recommended format |
|---|---|
| Photograph for web | WebP (fallback: JPEG) |
| Logo / icon with transparency | WebP or PNG |
| Screenshot with text | PNG |
| Animated image | WebP animated or MP4 |
| Maximum compression, modern browser | AVIF |
| Email attachment | JPEG or PNG |
| Image for editing / archiving | PNG or original RAW |
Converting Between Formats
Use the Convert tool to switch between any of these formats instantly. Upload your image, select the target format, adjust quality, and download — all processing happens server-side with no file size limits.