The alphabet soup of web images
Choosing the right image format used to be simple: JPEG for photos, PNG for graphics with transparency. Today, WebP and AVIF have crowded the field, and every performance audit tells you to serve "next-gen formats" for better Core Web Vitals.
But which format actually gives you the smallest file at acceptable quality? There is no single winner. Each format has distinct strengths depending on the visual content. Here is how to pick.
MozJPEG: The king of compatibility
Do not write off JPEG just yet. While standard JPEGs can be bulky, modern WebAssembly encoders like MozJPEG breathe new life into the format.
MozJPEG was purpose-built for the web. It applies smarter quantization tables and progressive scanning to squeeze bytes out of the format without visible loss. Real-world savings typically land between 30% and 60% compared to a standard camera JPEG, depending on the content of the photo.
When to use it: Use MozJPEG when you need absolute, 100% compatibility across every legacy browser, email client, and social media platform, but still want aggressive file size optimization.
OxiPNG: Lossless precision
PNG is completely lossless. It does not strip away any visual data to save space. An optimizer like OxiPNG works by trying different filter strategies and DEFLATE compression parameters to find the smallest valid encoding of the same pixel data.
Because no information is discarded, file size reductions are modest, typically 10% to 30%. In return, every single pixel stays identical to the original.
When to use it: Stick to PNG for high-fidelity graphic design, user interface screenshots, line art, or any image where crisp, pixel-perfect edges are mandatory.
WebP: The universal web standard
WebP is the current sweet spot for web publishing. It handles lossy compression well and, unlike JPEG, fully supports transparent backgrounds.
Re-encoding a typical PNG as lossy WebP can cut the file weight dramatically, often by 50% or more. Every modern browser supports it, making WebP the safest "next-gen" default for most sites.
When to use it: WebP should be your default choice for general-purpose web images, blog photos, and e-commerce product galleries.
AVIF: The next-generation heavyweight
AVIF is derived from the AV1 video codec and delivers some of the highest compression ratios available today. It regularly beats both JPEG and WebP on perceptual quality at equivalent file sizes, though exact savings vary widely by image content.
However, AVIF has a catch: it is extremely computationally expensive to encode. Compressing a high-resolution photo into AVIF inside your browser can take several seconds per image, making it slower for large batch jobs.
When to use it: Choose AVIF when bandwidth savings are your absolute highest priority, and you do not mind waiting a few extra seconds for the file to compress.
Test them yourself
The best way to know which format works for your specific image is to test it. The RaveTools Image Compressor lets you load any image and instantly toggle between MozJPEG, WebP, AVIF, and OxiPNG. You can use the before and after slider to check the visual quality and see the exact file size drop in real-time, all securely within your browser.