Why Image Format Matters
The format you choose for your website images directly affects page load speed, bandwidth costs, and user experience. A single hero image saved as an unoptimized JPG can weigh 500 KB or more. Convert that same image to AVIF and it drops to 250 KB with no visible quality loss. Multiply that savings across every image on every page, and the difference is measured in gigabytes of monthly bandwidth and hundreds of milliseconds off your largest contentful paint score. Format selection is not a cosmetic decision -- it is a performance decision with measurable impact on Core Web Vitals.
How We Test
Each comparison in this series uses a standardized test methodology. We compress a common set of source images (photographs, graphics with transparency, and animations) through each format at equivalent quality settings. File sizes are measured in bytes, not percentages from marketing materials. Visual quality is evaluated using SSIM (Structural Similarity Index), which quantifies how much perceptual detail is preserved after compression. Browser support data comes from Can I Use, updated monthly. Encoding and decoding speeds are benchmarked on commodity hardware to reflect real-world build pipelines, not idealized lab conditions.
Which Comparison to Read First
If you currently serve JPG photographs on your site, start with AVIF vs JPG to see whether the 50% file size savings justifies adding a modern format to your pipeline. If your site relies on transparent PNGs for logos and UI assets, PNG vs WebP covers the most direct upgrade path. Working with animated content? GIF vs WebP shows how to cut animation file sizes by 64-75%. For teams already using one modern format and considering the other, AVIF vs WebP breaks down the tradeoffs between compression ratio and encoding speed. And if you shoot on iPhone and need to get photos onto the web, HEIC vs JPG explains the conversion workflow.