JPEG

The core algorithm of JPEG image compression is the Discrete Cosine Transform (DCT); images are divided into 8×8 pixel blocks, and after each block undergoes a frequency-domain transform, high-frequency detail information is selectively discarded.

Compared to traditional JPEG at the same visual quality, HEIC file sizes are typically 40–50% smaller, while also supporting 16-bit color depth, HDR, and alpha channels.

JPEG压缩中quality参数本质上控制的是量化步长，值越低丢弃的高频信息越多，文件越小但细节损失越大

JPEG quality参数85被广泛推荐为黄金值，因为人类视觉系统对亮度变化比色彩变化更敏感，JPEG在此参数下能保留绝大多数亮度细节同时大幅削减冗余色彩数据

以quality=75压缩一张569,826字节的JPEG图片后，文件缩小到376,630字节，压缩率为33%

JPEG quality参数85~90几乎无肉眼可见差异，75~85有轻微差异适合网页使用，低于75可能出现可见压缩痕迹

In depth estimation research, using RAW frames rather than compressed formats such as JPEG can avoid artifacts and dynamic range compression introduced by post-processing, more faithfully reflecting the lighting information captured by the sensor.

LSB steganography has large capacity but is not resistant to compression; hidden information may be lost when the image is re-encoded (such as converted to JPEG).

The WebP format supports an alpha channel, whereas the JPEG format does not support an alpha channel at all.

WebP and AVIF formats are generally smaller than JPEG/PNG at the same quality, but browser compatibility must be considered, and a fallback can be provided via the `<picture>` element with `srcset`.

PNG uses lossless compression and preserves exact pixel values, so it is the only safe choice for line art; if a platform forces JPEG, quality should be set to 95 or above, and enlarged spot checks should be done before uploading.

JPEG stands for Joint Photographic Experts Group.

The JPEG standard was developed by a committee jointly formed by ISO/IEC and ITU-T, and the first standard was released in 1992.

Lossless compression merely re-encodes the data and can be fully restored after decompression, making it suitable for text and vector graphics; lossy compression discards some information, usually reducing resolution or increasing the compression rate for images, with a marked reduction in size but a loss of detail.

Traditional JPEG uses the DCT (Discrete Cosine Transform) algorithm established in 1992.

The core patents of JPEG have long expired, and any platform can implement it for free.

At the same image quality, WebP is typically 25%–35% smaller than JPEG.

For new projects, WebP can be used as the default directly; for pages requiring extreme performance, the picture tag can be used with AVIF as the first choice, WebP as the fallback, and JPEG as the final fallback.

JPEG image compression uses the Discrete Cosine Transform (DCT) to decompose 8×8 pixel blocks into spatial frequency components and then quantizes and discards the high-frequency coefficients.

JPEG XL supports lossless recompression of existing JPEG files, saving an average of about 20% in file size, and the files can be fully restored to the original JPEG.