Compress JPEG Files: A Guide to Optimal Quality

How to Compress JPEG Files: A Guide to Optimal Quality JPEG compression is a balancing act. Compress too little and you're serving 3MB photos to mobile users. Compress too hard and your product images look like watercolors. Get it right and you have images that look sharp, load fast, and don't bloat your site. This guide covers how JPEG compression actually works, what quality settings mean in practice, and which tool to use depending on your situation. How JPEG Compression Works JPEG compression uses a technique called the Discrete Cosine Transform (DCT). When you save a JPEG, the encoder: Splits the image into 8x8 pixel blocks Transforms each block into frequency data (low frequencies = broad color areas, high frequencies = sharp edges and fine detail) Applies a quantization table that rounds down the high-frequency data based on your quality setting Encodes the result with Huffman compression The quality parameter controls how aggressively step 3 discards detail. High quality = fine