概述
JPG在网络上已经主导了30年。WebP是由Google推出的，用以替代它。AVIF是最新的竞争者，提供三者中最佳的压缩效果。
本指南比较了三种格式在文件大小、质量、浏览器支持、透明度和易用性方面的表现。
正面比较
文件大小
JPG: JPG在相同质量下生成的文件最大。典型照片在JPG格式下可能为200KB。
WebP: WebP通常比JPG小25-35%，在相同视觉质量下。
Winner: AVIF（比JPG小50%）
图像质量
JPG: JPG在高压缩水平下显示压缩伪影。
WebP: WebP在相同文件大小下保持比JPG更好的质量，压缩伪影更少。
Winner: AVIF
浏览器支持
JPG: JPG在100%的浏览器和设备中得到支持。
WebP: WebP在所有现代浏览器中得到支持。全球支持率超过97%。
Winner: JPG
透明度
JPG: JPG根本不支持透明度。
WebP: WebP完全支持alpha通道透明度。
Winner: AVIF（最佳透明度压缩）
编码速度
JPG: JPG编码和解码速度极快。
WebP: WebP编码速度适中，比JPG稍慢。
Winner: JPG
Three Generations of Image Coding
These three formats represent successive generations of compression technology. JPG (1992) uses 8x8 DCT blocks with quantization, simple and effective for photographs but with no transparency and only lossy output.[1][2] WebP applies VP8-derived intra prediction plus transform coding and adds alpha, lossless, and animation support.[3] AVIF wraps still images coded with the AV1 video codec inside an ISO Base Media File Format container, bringing the most advanced prediction and partitioning tools of the three.[5][6]
Compression and Fidelity
Generally, for comparable quality AVIF produces the smallest files, WebP sits in the middle, and JPG is the largest, reflecting the increasing sophistication of each codec's prediction and entropy coding.[5] AVIF and WebP both support transparency and wide color, and AVIF additionally handles high dynamic range and high bit depth, capabilities absent from baseline JPG.[6][4]
Encoding Cost and Color Depth
The codecs differ markedly in encoding effort. JPG encodes almost instantly; WebP is moderately heavier; AVIF, derived from a video codec, is the most computationally expensive to encode, though decoding is fast.[5] JPG and WebP store 8 bits per color channel, while AVIF supports 10 and 12 bits, enabling smoother gradients and HDR. This higher bit depth is one reason AVIF is favored for high-quality and wide-gamut imagery.[6]
Standardization
JPEG is defined by ITU-T T.81 and ISO/IEC 10918.[1][2] WebP is specified in IETF RFC 9649.[3] AVIF is specified by the Alliance for Open Media and built on the royalty-free AV1 codec, which is a significant factor in its adoption since it avoids the patent-licensing complications attached to some codecs.[5][6]
Compatibility and Applications
JPG remains universally compatible and the safe default for interchange.[2] WebP enjoys broad modern-browser support and is a practical web upgrade. AVIF offers the best compression but has the youngest decoder ecosystem and slower encoding, so it is best where modern client support is assured and bandwidth savings are paramount. A common delivery strategy serves AVIF first, then WebP, then JPG as a fallback.[5]