What is Lossy Compression?
Lossy Compression — Lossy compression permanently removes data from an image file to achieve smaller file sizes. The removed data cannot be recovered. JPEG and WebP lossy are the most common lossy image formats; quality settings control how aggressively data is discarded.
Lossy compression reduces file size by permanently discarding image data that is less perceptible to the human eye. Unlike lossless compression, which allows perfect reconstruction of the original, lossy compression produces an approximation of the original — and each re-compression introduces additional data loss.
Most lossy image codecs exploit properties of human vision: we are less sensitive to high spatial frequencies (fine detail), to chroma differences than luminance differences, and to detail in peripheral vision. JPEG discards high-frequency DCT coefficients; WebP and AVIF use similar predictive coding techniques.
The degree of data loss is controlled by a quality parameter (0–100 in most tools, or a quantization parameter in some codecs). At high quality (85–95), lossy compression is visually lossless for photographs — the difference is detectable only by comparing the images side-by-side at 100% zoom. At low quality (30–60), artifacts (blocking, ringing, color banding) become clearly visible.
Lossy vs Lossless: When to Use Each
Use lossy compression for photographs, product images, and hero images where small file size is critical and minor quality reduction is acceptable. Use lossless compression for logos, icons, text-heavy images, UI screenshots, pixel art, and any image requiring exact pixel fidelity. For web delivery, lossy formats (JPEG, WebP, AVIF) are standard for photographs; PNG is standard for graphics.
Lossy Compression Tools on PicsSizer
Frequently Asked Questions
Can I recover data removed by lossy compression?▾
No. Once data is discarded by lossy compression, it cannot be recovered — the original pixels are gone. This is why you should always keep original uncompressed source files (RAW, PNG, TIFF) and export lossy JPEG/WebP only as the final output step.
Does compressing an already-compressed JPEG degrade it further?▾
Yes. Every time a JPEG is re-saved at a lossy quality setting, additional DCT quantization artifacts are introduced. The image degrades with each round-trip save. To minimize generational loss, save at a quality equal to or higher than the original compression, or work from the original lossless source.