Explainers · 8 min read · 2026-10-24
Two photos can look identical on screen and differ by a factor of twenty in file size. The difference is not the pixels you see - it is how much of the image the format decided you would never miss. Understanding that trade-off is the single most useful piece of image knowledge for anyone who builds web pages, sends photos over chat, or just keeps running out of phone storage.
Lossless formats (PNG, lossless WebP, TIFF) store the image exactly, and compress it the way ZIP compresses a document: by finding repeated patterns. If every pixel must survive untouched, the file size is driven by how complex the image is - a flat screenshot crushes down beautifully, a noisy photograph barely compresses at all. Lossy formats (JPEG, lossy WebP, AVIF) ask a different question: which details can the human eye safely lose? They discard colour precision the eye is bad at noticing, blur high-frequency texture, and round values toward their neighbours. The result is dramatically smaller files with changes that are nearly invisible - until you push too far and the artefacts show up as blocky edges and smudged gradients.
People often conflate shrinking an image's dimensions with compressing it. They are independent. Resizing a 4000-pixel-wide photo to 1200 pixels removes real information - that only makes sense if nobody will ever view it larger than 1200 pixels. Quality (the compression level) instead controls how faithfully the remaining pixels are described. A 1200-pixel image at quality 80 might be 180 KB; at quality 95 it might be 500 KB with a difference almost nobody can spot. For web images, quality 75-85 is the sweet spot most of the time.
Every time you re-save a JPEG, it re-compresses artefacts that were already introduced - quality compounds downward like a photocopy of a photocopy. Editing a photo in an app that exports JPEG, sending it through a chat that re-compresses it, then re-uploading it somewhere that compresses again can leave an image visibly degraded after three hops. The cure is to keep a pristine master (lossless, or the original camera file) and always export fresh from it.
Browser-based compressors decode your image locally, re-encode it with your chosen quality, and hand the result back - the file never leaves your device, which matters for anything private. Zoven's Image Compressor works exactly that way and handles batches, so you can drag fifty photos in, watch the total size drop, and download them in one go. Pair it with the Image Resizer when the dimensions are the real problem, and the Format Converter when a picky platform insists on a specific type.
Pick the format for the content: photographs get lossy (JPEG or WebP), flat graphics get lossless (PNG or SVG). Fighting that rule is where most oversized files come from.